Merge pull request #948 from littlefs-project/fix-sync-ordering

Fix sync issue where data writes could appear before metadata writes
Merge pull request #939 from Graveflo/master
2024-03-08 16:49:59 -06:00 · 2024-03-08 16:49:11 -06:00 · 2024-03-08 16:48:50 -06:00 · 2024-02-27 21:39:34 -06:00 · 2024-02-27 21:14:59 -06:00 · 2024-02-27 14:00:10 -06:00
35 changed files with 1724 additions and 536 deletions
--- a/.gitattributes
+++ b/.gitattributes
@@ -0,0 +1,4 @@
+# GitHub really wants to mark littlefs as a python project, telling it to
+# reclassify our test .toml files as C code (which they are 95% of anyways)
+# remedies this
+*.toml linguist-language=c
--- a/.github/workflows/post-release.yml
+++ b/.github/workflows/post-release.yml
@@ -10,7 +10,7 @@ defaults:

 jobs:
  post-release:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-latest
    steps:
      # trigger post-release in dependency repo, this indirection allows the
      # dependency repo to be updated often without affecting this repo. At
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -11,7 +11,7 @@ defaults:

 jobs:
  release:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-latest

    # need to manually check for a couple things
    # - tests passed?
@@ -81,7 +81,9 @@ jobs:
      - name: find-prev-version
        continue-on-error: true
        run: |
-          LFS_PREV_VERSION="$(git describe --tags --abbrev=0 --match 'v*')"
+          LFS_PREV_VERSION="$( \
+            git describe --tags --abbrev=0 --match 'v*' \
+            || true)"
          echo "LFS_PREV_VERSION=$LFS_PREV_VERSION"
          echo "LFS_PREV_VERSION=$LFS_PREV_VERSION" >> $GITHUB_ENV

@@ -102,7 +104,7 @@ jobs:
          # sizes table
          i=0
          j=0
-          for c in "" readonly threadsafe migrate error-asserts
+          for c in "" readonly threadsafe multiversion migrate error-asserts
          do
            # per-config results
            c_or_default=${c:-default}
@@ -110,7 +112,7 @@ jobs:
            table[$i,$j]=$c_camel
            ((j+=1))

-            for s in code stack struct
+            for s in code stack structs
            do
              f=sizes/thumb${c:+-$c}.$s.csv
              [ -e $f ] && table[$i,$j]=$( \
@@ -240,6 +242,7 @@ jobs:
        run: |
          # create release and patch version tag (vN.N.N)
          # only draft if not a patch release
+          touch release.txt
          [ -e table.txt ] && cat table.txt >> release.txt
          echo >> release.txt
          [ -e changes.txt ] && cat changes.txt >> release.txt
--- a/.github/workflows/status.yml
+++ b/.github/workflows/status.yml
@@ -11,7 +11,7 @@ defaults:
 jobs:
  # forward custom statuses
  status:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-latest
    steps:
      - uses: dawidd6/action-download-artifact@v2
        continue-on-error: true
@@ -60,7 +60,7 @@ jobs:

  # forward custom pr-comments
  comment:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-latest

    # only run on success (we don't want garbage comments!)
    if: ${{github.event.workflow_run.conclusion == 'success'}}
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -14,7 +14,7 @@ env:
 jobs:
  # run tests
  test:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-latest
    strategy:
      fail-fast: false
      matrix:
@@ -170,6 +170,27 @@ jobs:
          cp lfs.data.csv sizes/${{matrix.arch}}-threadsafe.data.csv
          cp lfs.stack.csv sizes/${{matrix.arch}}-threadsafe.stack.csv
          cp lfs.structs.csv sizes/${{matrix.arch}}-threadsafe.structs.csv
+      - name: sizes-multiversion
+        run: |
+          make clean
+          CFLAGS="$CFLAGS \
+            -DLFS_NO_ASSERT \
+            -DLFS_NO_DEBUG \
+            -DLFS_NO_WARN \
+            -DLFS_NO_ERROR \
+            -DLFS_MULTIVERSION" \
+            make lfs.code.csv lfs.data.csv lfs.stack.csv lfs.structs.csv
+          ./scripts/structs.py -u lfs.structs.csv
+          ./scripts/summary.py lfs.code.csv lfs.data.csv lfs.stack.csv \
+            -bfunction \
+            -fcode=code_size \
+            -fdata=data_size \
+            -fstack=stack_limit --max=stack_limit
+          mkdir -p sizes
+          cp lfs.code.csv sizes/${{matrix.arch}}-multiversion.code.csv
+          cp lfs.data.csv sizes/${{matrix.arch}}-multiversion.data.csv
+          cp lfs.stack.csv sizes/${{matrix.arch}}-multiversion.stack.csv
+          cp lfs.structs.csv sizes/${{matrix.arch}}-multiversion.structs.csv
      - name: sizes-migrate
        run: |
          make clean
@@ -308,7 +329,7 @@ jobs:
  #
  # this grows exponentially, so it doesn't turn out to be that many
  test-pls:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-latest
    strategy:
      fail-fast: false
      matrix:
@@ -338,7 +359,7 @@ jobs:

  # run with LFS_NO_INTRINSICS to make sure that works
  test-no-intrinsics:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - name: install
@@ -353,9 +374,45 @@ jobs:
        run: |
          CFLAGS="$CFLAGS -DLFS_NO_INTRINSICS" make test

+  # run LFS_MULTIVERSION tests
+  test-multiversion:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: install
+        run: |
+          # need a few things
+          sudo apt-get update -qq
+          sudo apt-get install -qq gcc python3 python3-pip
+          pip3 install toml
+          gcc --version
+          python3 --version
+      - name: test-multiversion
+        run: |
+          CFLAGS="$CFLAGS -DLFS_MULTIVERSION" make test
+
+  # run tests on the older version lfs2.0
+  test-lfs2_0:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: install
+        run: |
+          # need a few things
+          sudo apt-get update -qq
+          sudo apt-get install -qq gcc python3 python3-pip
+          pip3 install toml
+          gcc --version
+          python3 --version
+      - name: test-lfs2_0
+        run: |
+          CFLAGS="$CFLAGS -DLFS_MULTIVERSION" \
+          TESTFLAGS="$TESTFLAGS -DDISK_VERSION=0x00020000" \
+            make test
+
  # run under Valgrind to check for memory errors
  test-valgrind:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - name: install
@@ -371,12 +428,13 @@ jobs:
      # on one geometry
      - name: test-valgrind
        run: |
-          TESTFLAGS="$TESTFLAGS --valgrind -Gdefault -Pnone" make test
+          TESTFLAGS="$TESTFLAGS --valgrind --context=1024 -Gdefault -Pnone" \
+            make test

  # test that compilation is warning free under clang
  # run with Clang, mostly to check for Clang-specific warnings
  test-clang:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - name: install
@@ -399,7 +457,7 @@ jobs:
  #
  # note there's no real benefit to running these on multiple archs
  bench:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - name: install
@@ -475,7 +533,7 @@ jobs:

  # run compatibility tests using the current master as the previous version
  test-compat:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
        if: ${{github.event_name == 'pull_request'}}
@@ -511,7 +569,7 @@ jobs:

  # self-host with littlefs-fuse for a fuzz-like test
  fuse:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-latest
    if: ${{!endsWith(github.ref, '-prefix')}}
    steps:
      - uses: actions/checkout@v2
@@ -561,7 +619,7 @@ jobs:

  # test migration using littlefs-fuse
  migrate:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-latest
    if: ${{!endsWith(github.ref, '-prefix')}}
    steps:
      - uses: actions/checkout@v2
@@ -633,7 +691,7 @@ jobs:

  # status related tasks that run after tests
  status:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-latest
    needs: [test, bench]
    steps:
      - uses: actions/checkout@v2
@@ -684,7 +742,7 @@ jobs:
          # sizes table
          i=0
          j=0
-          for c in "" readonly threadsafe migrate error-asserts
+          for c in "" readonly threadsafe multiversion migrate error-asserts
          do
            # per-config results
            c_or_default=${c:-default}
--- a/DESIGN.md
+++ b/DESIGN.md
@@ -59,7 +59,7 @@ This leaves us with three major requirements for an embedded filesystem.
   RAM to temporarily store filesystem metadata.

   For ROM, this means we need to keep our design simple and reuse code paths
-   were possible. For RAM we have a stronger requirement, all RAM usage is
+   where possible. For RAM we have a stronger requirement, all RAM usage is
   bounded. This means RAM usage does not grow as the filesystem changes in
   size or number of files. This creates a unique challenge as even presumably
   simple operations, such as traversing the filesystem, become surprisingly
@@ -626,7 +626,7 @@ log&#8322;_n_ pointers that skip to different preceding elements of the
 skip-list.

 The name comes from heavy use of the [CTZ instruction][wikipedia-ctz], which
-lets us calculate the power-of-two factors efficiently. For a give block _n_,
+lets us calculate the power-of-two factors efficiently. For a given block _n_,
 that block contains ctz(_n_)+1 pointers.

 ```
--- a/3
+++ b/3
@@ -63,6 +63,7 @@ CFLAGS += -fcallgraph-info=su
 CFLAGS += -g3
 CFLAGS += -I.
 CFLAGS += -std=c99 -Wall -Wextra -pedantic
+CFLAGS += -Wmissing-prototypes
 CFLAGS += -ftrack-macro-expansion=0
 ifdef DEBUG
 CFLAGS += -O0
@@ -354,6 +355,7 @@ summary-diff sizes-diff: $(OBJ) $(CI)

 ## Build the test-runner
 .PHONY: test-runner build-test
+test-runner build-test: CFLAGS+=-Wno-missing-prototypes
 ifndef NO_COV
 test-runner build-test: CFLAGS+=--coverage
 endif
@@ -405,6 +407,7 @@ testmarks-diff: $(TEST_CSV)

 ## Build the bench-runner
 .PHONY: bench-runner build-bench
+bench-runner build-bench: CFLAGS+=-Wno-missing-prototypes
 ifdef YES_COV
 bench-runner build-bench: CFLAGS+=--coverage
 endif
--- a/README.md
+++ b/README.md
@@ -250,10 +250,17 @@ License Identifiers that are here available: http://spdx.org/licenses/
  MCUs. It offers static wear-leveling and power-resilience with only a fixed
  _O(|address|)_ pointer structure stored on each block and in RAM.

+- [ChaN's FatFs] - A lightweight reimplementation of the infamous FAT filesystem
+  for microcontroller-scale devices. Due to limitations of FAT it can't provide
+  power-loss resilience, but it does allow easy interop with PCs.
+
 - [chamelon] - A pure-OCaml implementation of (most of) littlefs, designed for
  use with the MirageOS library operating system project. It is interoperable
  with the reference implementation, with some caveats.

+- [nim-littlefs] - A Nim wrapper and API for littlefs. Includes a fuse 
+  implementation based on [littlefs-fuse]
+
 [BSD-3-Clause]: https://spdx.org/licenses/BSD-3-Clause.html
 [littlefs-disk-img-viewer]: https://github.com/tniessen/littlefs-disk-img-viewer
 [littlefs-fuse]: https://github.com/geky/littlefs-fuse
@@ -266,6 +273,8 @@ License Identifiers that are here available: http://spdx.org/licenses/
 [LittleFileSystem]: https://os.mbed.com/docs/mbed-os/latest/apis/littlefilesystem.html
 [SPIFFS]: https://github.com/pellepl/spiffs
 [Dhara]: https://github.com/dlbeer/dhara
+[ChaN's FatFs]: http://elm-chan.org/fsw/ff/00index_e.html
 [littlefs-python]: https://pypi.org/project/littlefs-python/
 [littlefs2-rust]: https://crates.io/crates/littlefs2
 [chamelon]: https://github.com/yomimono/chamelon
+[nim-littlefs]: https://github.com/Graveflo/nim-littlefs
--- a/bd/lfs_emubd.c
+++ b/bd/lfs_emubd.c
@@ -48,6 +48,7 @@ static void lfs_emubd_decblock(lfs_emubd_block_t *block) {
 static lfs_emubd_block_t *lfs_emubd_mutblock(
        const struct lfs_config *cfg,
        lfs_emubd_block_t **block) {
+    lfs_emubd_t *bd = cfg->context;
    lfs_emubd_block_t *block_ = *block;
    if (block_ && block_->rc == 1) {
        // rc == 1? can modify
@@ -56,13 +57,13 @@ static lfs_emubd_block_t *lfs_emubd_mutblock(
    } else if (block_) {
        // rc > 1? need to create a copy
        lfs_emubd_block_t *nblock = malloc(
-                sizeof(lfs_emubd_block_t) + cfg->block_size);
+                sizeof(lfs_emubd_block_t) + bd->cfg->erase_size);
        if (!nblock) {
            return NULL;
        }

        memcpy(nblock, block_,
-                sizeof(lfs_emubd_block_t) + cfg->block_size);
+                sizeof(lfs_emubd_block_t) + bd->cfg->erase_size);
        nblock->rc = 1;

        lfs_emubd_decblock(block_);
@@ -72,7 +73,7 @@ static lfs_emubd_block_t *lfs_emubd_mutblock(
    } else {
        // no block? need to allocate
        lfs_emubd_block_t *nblock = malloc(
-                sizeof(lfs_emubd_block_t) + cfg->block_size);
+                sizeof(lfs_emubd_block_t) + bd->cfg->erase_size);
        if (!nblock) {
            return NULL;
        }
@@ -81,10 +82,9 @@ static lfs_emubd_block_t *lfs_emubd_mutblock(
        nblock->wear = 0;

        // zero for consistency
-        lfs_emubd_t *bd = cfg->context;
        memset(nblock->data,
                (bd->cfg->erase_value != -1) ? bd->cfg->erase_value : 0,
-                cfg->block_size);
+                bd->cfg->erase_size);

        *block = nblock;
        return nblock;
@@ -94,22 +94,22 @@ static lfs_emubd_block_t *lfs_emubd_mutblock(

 // emubd create/destroy

-int lfs_emubd_createcfg(const struct lfs_config *cfg, const char *path,
+int lfs_emubd_create(const struct lfs_config *cfg,
        const struct lfs_emubd_config *bdcfg) {
-    LFS_EMUBD_TRACE("lfs_emubd_createcfg(%p {.context=%p, "
-                ".read=%p, .prog=%p, .erase=%p, .sync=%p, "
-                ".read_size=%"PRIu32", .prog_size=%"PRIu32", "
-                ".block_size=%"PRIu32", .block_count=%"PRIu32"}, "
-                "\"%s\", "
-                "%p {.erase_value=%"PRId32", .erase_cycles=%"PRIu32", "
+    LFS_EMUBD_TRACE("lfs_emubd_create(%p {.context=%p, "
+                ".read=%p, .prog=%p, .erase=%p, .sync=%p}, "
+                "%p {.read_size=%"PRIu32", .prog_size=%"PRIu32", "
+                ".erase_size=%"PRIu32", .erase_count=%"PRIu32", "
+                ".erase_value=%"PRId32", .erase_cycles=%"PRIu32", "
                ".badblock_behavior=%"PRIu8", .power_cycles=%"PRIu32", "
                ".powerloss_behavior=%"PRIu8", .powerloss_cb=%p, "
                ".powerloss_data=%p, .track_branches=%d})",
            (void*)cfg, cfg->context,
            (void*)(uintptr_t)cfg->read, (void*)(uintptr_t)cfg->prog,
            (void*)(uintptr_t)cfg->erase, (void*)(uintptr_t)cfg->sync,
-            cfg->read_size, cfg->prog_size, cfg->block_size, cfg->block_count,
-            path, (void*)bdcfg, bdcfg->erase_value, bdcfg->erase_cycles,
+            (void*)bdcfg,
+            bdcfg->read_size, bdcfg->prog_size, bdcfg->erase_size,
+            bdcfg->erase_count, bdcfg->erase_value, bdcfg->erase_cycles,
            bdcfg->badblock_behavior, bdcfg->power_cycles,
            bdcfg->powerloss_behavior, (void*)(uintptr_t)bdcfg->powerloss_cb,
            bdcfg->powerloss_data, bdcfg->track_branches);
@@ -117,24 +117,26 @@ int lfs_emubd_createcfg(const struct lfs_config *cfg, const char *path,
    bd->cfg = bdcfg;

    // allocate our block array, all blocks start as uninitialized
-    bd->blocks = malloc(cfg->block_count * sizeof(lfs_emubd_block_t*));
+    bd->blocks = malloc(bd->cfg->erase_count * sizeof(lfs_emubd_block_t*));
    if (!bd->blocks) {
-        LFS_EMUBD_TRACE("lfs_emubd_createcfg -> %d", LFS_ERR_NOMEM);
+        LFS_EMUBD_TRACE("lfs_emubd_create -> %d", LFS_ERR_NOMEM);
        return LFS_ERR_NOMEM;
    }
-    memset(bd->blocks, 0, cfg->block_count * sizeof(lfs_emubd_block_t*));
+    memset(bd->blocks, 0, bd->cfg->erase_count * sizeof(lfs_emubd_block_t*));

    // setup testing things
    bd->readed = 0;
    bd->proged = 0;
    bd->erased = 0;
    bd->power_cycles = bd->cfg->power_cycles;
+    bd->ooo_block = -1;
+    bd->ooo_data = NULL;
    bd->disk = NULL;

    if (bd->cfg->disk_path) {
        bd->disk = malloc(sizeof(lfs_emubd_disk_t));
        if (!bd->disk) {
-            LFS_EMUBD_TRACE("lfs_emubd_createcfg -> %d", LFS_ERR_NOMEM);
+            LFS_EMUBD_TRACE("lfs_emubd_create -> %d", LFS_ERR_NOMEM);
            return LFS_ERR_NOMEM;
        }
        bd->disk->rc = 1;
@@ -156,21 +158,21 @@ int lfs_emubd_createcfg(const struct lfs_config *cfg, const char *path,
        // if we're emulating erase values, we can keep a block around in
        // memory of just the erase state to speed up emulated erases
        if (bd->cfg->erase_value != -1) {
-            bd->disk->scratch = malloc(cfg->block_size);
+            bd->disk->scratch = malloc(bd->cfg->erase_size);
            if (!bd->disk->scratch) {
-                LFS_EMUBD_TRACE("lfs_emubd_createcfg -> %d", LFS_ERR_NOMEM);
+                LFS_EMUBD_TRACE("lfs_emubd_create -> %d", LFS_ERR_NOMEM);
                return LFS_ERR_NOMEM;
            }
            memset(bd->disk->scratch,
                    bd->cfg->erase_value,
-                    cfg->block_size);
+                    bd->cfg->erase_size);

            // go ahead and erase all of the disk, otherwise the file will not
            // match our internal representation
-            for (size_t i = 0; i < cfg->block_count; i++) {
+            for (size_t i = 0; i < bd->cfg->erase_count; i++) {
                ssize_t res = write(bd->disk->fd,
                        bd->disk->scratch,
-                        cfg->block_size);
+                        bd->cfg->erase_size);
                if (res < 0) {
                    int err = -errno;
                    LFS_EMUBD_TRACE("lfs_emubd_create -> %d", err);
@@ -180,38 +182,22 @@ int lfs_emubd_createcfg(const struct lfs_config *cfg, const char *path,
        }
    }

-    LFS_EMUBD_TRACE("lfs_emubd_createcfg -> %d", 0);
+    LFS_EMUBD_TRACE("lfs_emubd_create -> %d", 0);
    return 0;
 }

-int lfs_emubd_create(const struct lfs_config *cfg, const char *path) {
-    LFS_EMUBD_TRACE("lfs_emubd_create(%p {.context=%p, "
-                ".read=%p, .prog=%p, .erase=%p, .sync=%p, "
-                ".read_size=%"PRIu32", .prog_size=%"PRIu32", "
-                ".block_size=%"PRIu32", .block_count=%"PRIu32"}, "
-                "\"%s\")",
-            (void*)cfg, cfg->context,
-            (void*)(uintptr_t)cfg->read, (void*)(uintptr_t)cfg->prog,
-            (void*)(uintptr_t)cfg->erase, (void*)(uintptr_t)cfg->sync,
-            cfg->read_size, cfg->prog_size, cfg->block_size, cfg->block_count,
-            path);
-    static const struct lfs_emubd_config defaults = {.erase_value=-1};
-    int err = lfs_emubd_createcfg(cfg, path, &defaults);
-    LFS_EMUBD_TRACE("lfs_emubd_create -> %d", err);
-    return err;
-}
-
 int lfs_emubd_destroy(const struct lfs_config *cfg) {
    LFS_EMUBD_TRACE("lfs_emubd_destroy(%p)", (void*)cfg);
    lfs_emubd_t *bd = cfg->context;

    // decrement reference counts
-    for (lfs_block_t i = 0; i < cfg->block_count; i++) {
+    for (lfs_block_t i = 0; i < bd->cfg->erase_count; i++) {
        lfs_emubd_decblock(bd->blocks[i]);
    }
    free(bd->blocks);

    // clean up other resources 
+    lfs_emubd_decblock(bd->ooo_data);
    if (bd->disk) {
        bd->disk->rc -= 1;
        if (bd->disk->rc == 0) {
@@ -226,6 +212,75 @@ int lfs_emubd_destroy(const struct lfs_config *cfg) {
 }


+// powerloss hook
+static int lfs_emubd_powerloss(const struct lfs_config *cfg) {
+    lfs_emubd_t *bd = cfg->context;
+
+    // emulate out-of-order writes?
+    lfs_emubd_block_t *ooo_data = NULL;
+    if (bd->cfg->powerloss_behavior == LFS_EMUBD_POWERLOSS_OOO
+            && bd->ooo_block != -1) {
+        // since writes between syncs are allowed to be out-of-order, it
+        // shouldn't hurt to restore the first write on powerloss, right?
+        ooo_data = bd->blocks[bd->ooo_block];
+        bd->blocks[bd->ooo_block] = lfs_emubd_incblock(bd->ooo_data);
+
+        // mirror to disk file?
+        if (bd->disk
+                && (bd->blocks[bd->ooo_block]
+                    || bd->cfg->erase_value != -1)) {
+            off_t res1 = lseek(bd->disk->fd,
+                    (off_t)bd->ooo_block*bd->cfg->erase_size,
+                    SEEK_SET);
+            if (res1 < 0) {
+                return -errno;
+            }
+
+            ssize_t res2 = write(bd->disk->fd,
+                    (bd->blocks[bd->ooo_block])
+                        ? bd->blocks[bd->ooo_block]->data
+                        : bd->disk->scratch,
+                    bd->cfg->erase_size);
+            if (res2 < 0) {
+                return -errno;
+            }
+        }
+    }
+
+    // simulate power loss
+    bd->cfg->powerloss_cb(bd->cfg->powerloss_data);
+
+    // if we continue, undo out-of-order write emulation
+    if (bd->cfg->powerloss_behavior == LFS_EMUBD_POWERLOSS_OOO
+            && bd->ooo_block != -1) {
+        lfs_emubd_decblock(bd->blocks[bd->ooo_block]);
+        bd->blocks[bd->ooo_block] = ooo_data;
+
+        // mirror to disk file?
+        if (bd->disk
+                && (bd->blocks[bd->ooo_block]
+                    || bd->cfg->erase_value != -1)) {
+            off_t res1 = lseek(bd->disk->fd,
+                    (off_t)bd->ooo_block*bd->cfg->erase_size,
+                    SEEK_SET);
+            if (res1 < 0) {
+                return -errno;
+            }
+
+            ssize_t res2 = write(bd->disk->fd,
+                    (bd->blocks[bd->ooo_block])
+                        ? bd->blocks[bd->ooo_block]->data
+                        : bd->disk->scratch,
+                    bd->cfg->erase_size);
+            if (res2 < 0) {
+                return -errno;
+            }
+        }
+    }
+
+    return 0;
+}
+

 // block device API

@@ -237,10 +292,10 @@ int lfs_emubd_read(const struct lfs_config *cfg, lfs_block_t block,
    lfs_emubd_t *bd = cfg->context;

    // check if read is valid
-    LFS_ASSERT(block < cfg->block_count);
-    LFS_ASSERT(off  % cfg->read_size == 0);
-    LFS_ASSERT(size % cfg->read_size == 0);
-    LFS_ASSERT(off+size <= cfg->block_size);
+    LFS_ASSERT(block < bd->cfg->erase_count);
+    LFS_ASSERT(off  % bd->cfg->read_size == 0);
+    LFS_ASSERT(size % bd->cfg->read_size == 0);
+    LFS_ASSERT(off+size <= bd->cfg->erase_size);

    // get the block
    const lfs_emubd_block_t *b = bd->blocks[block];
@@ -287,10 +342,10 @@ int lfs_emubd_prog(const struct lfs_config *cfg, lfs_block_t block,
    lfs_emubd_t *bd = cfg->context;

    // check if write is valid
-    LFS_ASSERT(block < cfg->block_count);
-    LFS_ASSERT(off  % cfg->prog_size == 0);
-    LFS_ASSERT(size % cfg->prog_size == 0);
-    LFS_ASSERT(off+size <= cfg->block_size);
+    LFS_ASSERT(block < bd->cfg->erase_count);
+    LFS_ASSERT(off  % bd->cfg->prog_size == 0);
+    LFS_ASSERT(size % bd->cfg->prog_size == 0);
+    LFS_ASSERT(off+size <= bd->cfg->erase_size);

    // get the block
    lfs_emubd_block_t *b = lfs_emubd_mutblock(cfg, &bd->blocks[block]);
@@ -327,7 +382,7 @@ int lfs_emubd_prog(const struct lfs_config *cfg, lfs_block_t block,
    // mirror to disk file?
    if (bd->disk) {
        off_t res1 = lseek(bd->disk->fd,
-                (off_t)block*cfg->block_size + (off_t)off,
+                (off_t)block*bd->cfg->erase_size + (off_t)off,
                SEEK_SET);
        if (res1 < 0) {
            int err = -errno;
@@ -361,8 +416,11 @@ int lfs_emubd_prog(const struct lfs_config *cfg, lfs_block_t block,
    if (bd->power_cycles > 0) {
        bd->power_cycles -= 1;
        if (bd->power_cycles == 0) {
-            // simulate power loss
-            bd->cfg->powerloss_cb(bd->cfg->powerloss_data);
+            int err = lfs_emubd_powerloss(cfg);
+            if (err) {
+                LFS_EMUBD_TRACE("lfs_emubd_prog -> %d", err);
+                return err;
+            }
        }
    }

@@ -372,16 +430,23 @@ int lfs_emubd_prog(const struct lfs_config *cfg, lfs_block_t block,

 int lfs_emubd_erase(const struct lfs_config *cfg, lfs_block_t block) {
    LFS_EMUBD_TRACE("lfs_emubd_erase(%p, 0x%"PRIx32" (%"PRIu32"))",
-            (void*)cfg, block, cfg->block_size);
+            (void*)cfg, block, ((lfs_emubd_t*)cfg->context)->cfg->erase_size);
    lfs_emubd_t *bd = cfg->context;

    // check if erase is valid
-    LFS_ASSERT(block < cfg->block_count);
+    LFS_ASSERT(block < bd->cfg->erase_count);
+
+    // emulate out-of-order writes? save first write
+    if (bd->cfg->powerloss_behavior == LFS_EMUBD_POWERLOSS_OOO
+            && bd->ooo_block == -1) {
+        bd->ooo_block = block;
+        bd->ooo_data = lfs_emubd_incblock(bd->blocks[block]);
+    }

    // get the block
    lfs_emubd_block_t *b = lfs_emubd_mutblock(cfg, &bd->blocks[block]);
    if (!b) {
-        LFS_EMUBD_TRACE("lfs_emubd_prog -> %d", LFS_ERR_NOMEM);
+        LFS_EMUBD_TRACE("lfs_emubd_erase -> %d", LFS_ERR_NOMEM);
        return LFS_ERR_NOMEM;
    }

@@ -405,12 +470,12 @@ int lfs_emubd_erase(const struct lfs_config *cfg, lfs_block_t block) {

    // emulate an erase value?
    if (bd->cfg->erase_value != -1) {
-        memset(b->data, bd->cfg->erase_value, cfg->block_size);
+        memset(b->data, bd->cfg->erase_value, bd->cfg->erase_size);

        // mirror to disk file?
        if (bd->disk) {
            off_t res1 = lseek(bd->disk->fd,
-                    (off_t)block*cfg->block_size,
+                    (off_t)block*bd->cfg->erase_size,
                    SEEK_SET);
            if (res1 < 0) {
                int err = -errno;
@@ -420,7 +485,7 @@ int lfs_emubd_erase(const struct lfs_config *cfg, lfs_block_t block) {

            ssize_t res2 = write(bd->disk->fd,
                    bd->disk->scratch,
-                    cfg->block_size);
+                    bd->cfg->erase_size);
            if (res2 < 0) {
                int err = -errno;
                LFS_EMUBD_TRACE("lfs_emubd_erase -> %d", err);
@@ -430,7 +495,7 @@ int lfs_emubd_erase(const struct lfs_config *cfg, lfs_block_t block) {
    }

    // track erases
-    bd->erased += cfg->block_size;
+    bd->erased += bd->cfg->erase_size;
    if (bd->cfg->erase_sleep) {
        int err = nanosleep(&(struct timespec){
                .tv_sec=bd->cfg->erase_sleep/1000000000,
@@ -447,8 +512,11 @@ int lfs_emubd_erase(const struct lfs_config *cfg, lfs_block_t block) {
    if (bd->power_cycles > 0) {
        bd->power_cycles -= 1;
        if (bd->power_cycles == 0) {
-            // simulate power loss
-            bd->cfg->powerloss_cb(bd->cfg->powerloss_data);
+            int err = lfs_emubd_powerloss(cfg);
+            if (err) {
+                LFS_EMUBD_TRACE("lfs_emubd_erase -> %d", err);
+                return err;
+            }
        }
    }

@@ -458,17 +526,24 @@ int lfs_emubd_erase(const struct lfs_config *cfg, lfs_block_t block) {

 int lfs_emubd_sync(const struct lfs_config *cfg) {
    LFS_EMUBD_TRACE("lfs_emubd_sync(%p)", (void*)cfg);
+    lfs_emubd_t *bd = cfg->context;

-    // do nothing
-    (void)cfg;
+    // emulate out-of-order writes? reset first write, writes
+    // cannot be out-of-order across sync
+    if (bd->cfg->powerloss_behavior == LFS_EMUBD_POWERLOSS_OOO) {
+        lfs_emubd_decblock(bd->ooo_data);
+        bd->ooo_block = -1;
+        bd->ooo_data = NULL;
+    }

    LFS_EMUBD_TRACE("lfs_emubd_sync -> %d", 0);
    return 0;
 }

+
 /// Additional extended API for driving test features ///

-static int lfs_emubd_rawcrc(const struct lfs_config *cfg,
+static int lfs_emubd_crc_(const struct lfs_config *cfg,
        lfs_block_t block, uint32_t *crc) {
    lfs_emubd_t *bd = cfg->context;

@@ -497,7 +572,7 @@ int lfs_emubd_crc(const struct lfs_config *cfg,
        lfs_block_t block, uint32_t *crc) {
    LFS_EMUBD_TRACE("lfs_emubd_crc(%p, %"PRIu32", %p)",
            (void*)cfg, block, crc);
-    int err = lfs_emubd_rawcrc(cfg, block, crc);
+    int err = lfs_emubd_crc_(cfg, block, crc);
    LFS_EMUBD_TRACE("lfs_emubd_crc -> %d", err);
    return err;
 }
@@ -508,7 +583,7 @@ int lfs_emubd_bdcrc(const struct lfs_config *cfg, uint32_t *crc) {
    uint32_t crc_ = 0xffffffff;
    for (lfs_block_t i = 0; i < cfg->block_count; i++) {
        uint32_t i_crc;
-        int err = lfs_emubd_rawcrc(cfg, i, &i_crc);
+        int err = lfs_emubd_crc_(cfg, i, &i_crc);
        if (err) {
            LFS_EMUBD_TRACE("lfs_emubd_bdcrc -> %d", err);
            return err;
@@ -573,7 +648,7 @@ lfs_emubd_swear_t lfs_emubd_wear(const struct lfs_config *cfg,
    lfs_emubd_t *bd = cfg->context;

    // check if block is valid
-    LFS_ASSERT(block < cfg->block_count);
+    LFS_ASSERT(block < bd->cfg->erase_count);

    // get the wear
    lfs_emubd_wear_t wear;
@@ -595,7 +670,7 @@ int lfs_emubd_setwear(const struct lfs_config *cfg,
    lfs_emubd_t *bd = cfg->context;

    // check if block is valid
-    LFS_ASSERT(block < cfg->block_count);
+    LFS_ASSERT(block < bd->cfg->erase_count);

    // set the wear
    lfs_emubd_block_t *b = lfs_emubd_mutblock(cfg, &bd->blocks[block]);
@@ -635,13 +710,13 @@ int lfs_emubd_copy(const struct lfs_config *cfg, lfs_emubd_t *copy) {
    lfs_emubd_t *bd = cfg->context;

    // lazily copy over our block array
-    copy->blocks = malloc(cfg->block_count * sizeof(lfs_emubd_block_t*));
+    copy->blocks = malloc(bd->cfg->erase_count * sizeof(lfs_emubd_block_t*));
    if (!copy->blocks) {
        LFS_EMUBD_TRACE("lfs_emubd_copy -> %d", LFS_ERR_NOMEM);
        return LFS_ERR_NOMEM;
    }

-    for (size_t i = 0; i < cfg->block_count; i++) {
+    for (size_t i = 0; i < bd->cfg->erase_count; i++) {
        copy->blocks[i] = lfs_emubd_incblock(bd->blocks[i]);
    }

@@ -650,6 +725,8 @@ int lfs_emubd_copy(const struct lfs_config *cfg, lfs_emubd_t *copy) {
    copy->proged = bd->proged;
    copy->erased = bd->erased;
    copy->power_cycles = bd->power_cycles;
+    copy->ooo_block = bd->ooo_block;
+    copy->ooo_data = lfs_emubd_incblock(bd->ooo_data);
    copy->disk = bd->disk;
    if (copy->disk) {
        copy->disk->rc += 1;
--- a/bd/lfs_emubd.h
+++ b/bd/lfs_emubd.h
@@ -36,17 +36,18 @@ extern "C"
 // Not that read-noop is not allowed. Read _must_ return a consistent (but
 // may be arbitrary) value on every read.
 typedef enum lfs_emubd_badblock_behavior {
-    LFS_EMUBD_BADBLOCK_PROGERROR,
-    LFS_EMUBD_BADBLOCK_ERASEERROR,
-    LFS_EMUBD_BADBLOCK_READERROR,
-    LFS_EMUBD_BADBLOCK_PROGNOOP,
-    LFS_EMUBD_BADBLOCK_ERASENOOP,
+    LFS_EMUBD_BADBLOCK_PROGERROR  = 0, // Error on prog
+    LFS_EMUBD_BADBLOCK_ERASEERROR = 1, // Error on erase
+    LFS_EMUBD_BADBLOCK_READERROR  = 2, // Error on read
+    LFS_EMUBD_BADBLOCK_PROGNOOP   = 3, // Prog does nothing silently
+    LFS_EMUBD_BADBLOCK_ERASENOOP  = 4, // Erase does nothing silently
 } lfs_emubd_badblock_behavior_t;

 // Mode determining how power-loss behaves during testing. For now this
 // only supports a noop behavior, leaving the data on-disk untouched.
 typedef enum lfs_emubd_powerloss_behavior {
-    LFS_EMUBD_POWERLOSS_NOOP,
+    LFS_EMUBD_POWERLOSS_NOOP = 0, // Progs are atomic
+    LFS_EMUBD_POWERLOSS_OOO  = 1, // Blocks are written out-of-order
 } lfs_emubd_powerloss_behavior_t;

 // Type for measuring read/program/erase operations
@@ -67,6 +68,18 @@ typedef int64_t lfs_emubd_ssleep_t;

 // emubd config, this is required for testing
 struct lfs_emubd_config {
+    // Minimum size of a read operation in bytes.
+    lfs_size_t read_size;
+
+    // Minimum size of a program operation in bytes.
+    lfs_size_t prog_size;
+
+    // Size of an erase operation in bytes.
+    lfs_size_t erase_size;
+
+    // Number of erase blocks on the device.
+    lfs_size_t erase_count;
+
    // 8-bit erase value to use for simulating erases. -1 does not simulate
    // erases, which can speed up testing by avoiding the extra block-device
    // operations to store the erase value.
@@ -140,6 +153,8 @@ typedef struct lfs_emubd {
    lfs_emubd_io_t proged;
    lfs_emubd_io_t erased;
    lfs_emubd_powercycles_t power_cycles;
+    lfs_ssize_t ooo_block;
+    lfs_emubd_block_t *ooo_data;
    lfs_emubd_disk_t *disk;

    const struct lfs_emubd_config *cfg;
@@ -149,11 +164,7 @@ typedef struct lfs_emubd {
 /// Block device API ///

 // Create an emulating block device using the geometry in lfs_config
-//
-// Note that filebd is used if a path is provided, if path is NULL
-// emubd will use rambd which can be much faster.
-int lfs_emubd_create(const struct lfs_config *cfg, const char *path);
-int lfs_emubd_createcfg(const struct lfs_config *cfg, const char *path,
+int lfs_emubd_create(const struct lfs_config *cfg,
        const struct lfs_emubd_config *bdcfg);

 // Clean up memory associated with block device
--- a/bd/lfs_filebd.c
+++ b/bd/lfs_filebd.c
@@ -15,18 +15,22 @@
 #include <windows.h>
 #endif

-int lfs_filebd_create(const struct lfs_config *cfg, const char *path) {
+int lfs_filebd_create(const struct lfs_config *cfg, const char *path,
+        const struct lfs_filebd_config *bdcfg) {
    LFS_FILEBD_TRACE("lfs_filebd_create(%p {.context=%p, "
-                ".read=%p, .prog=%p, .erase=%p, .sync=%p, "
-                ".read_size=%"PRIu32", .prog_size=%"PRIu32", "
-                ".block_size=%"PRIu32", .block_count=%"PRIu32"}, "
-                "\"%s\")",
+                ".read=%p, .prog=%p, .erase=%p, .sync=%p}, "
+                "\"%s\", "
+                "%p {.read_size=%"PRIu32", .prog_size=%"PRIu32", "
+                ".erase_size=%"PRIu32", .erase_count=%"PRIu32"})",
            (void*)cfg, cfg->context,
            (void*)(uintptr_t)cfg->read, (void*)(uintptr_t)cfg->prog,
            (void*)(uintptr_t)cfg->erase, (void*)(uintptr_t)cfg->sync,
-            cfg->read_size, cfg->prog_size, cfg->block_size, cfg->block_count,
-            path, (void*)bdcfg, bdcfg->erase_value);
+            path,
+            (void*)bdcfg,
+            bdcfg->read_size, bdcfg->prog_size, bdcfg->erase_size,
+            bdcfg->erase_count);
    lfs_filebd_t *bd = cfg->context;
+    bd->cfg = bdcfg;

    // open file
    #ifdef _WIN32
@@ -66,17 +70,17 @@ int lfs_filebd_read(const struct lfs_config *cfg, lfs_block_t block,
    lfs_filebd_t *bd = cfg->context;

    // check if read is valid
-    LFS_ASSERT(block < cfg->block_count);
-    LFS_ASSERT(off  % cfg->read_size == 0);
-    LFS_ASSERT(size % cfg->read_size == 0);
-    LFS_ASSERT(off+size <= cfg->block_size);
+    LFS_ASSERT(block < bd->cfg->erase_count);
+    LFS_ASSERT(off  % bd->cfg->read_size == 0);
+    LFS_ASSERT(size % bd->cfg->read_size == 0);
+    LFS_ASSERT(off+size <= bd->cfg->erase_size);

    // zero for reproducibility (in case file is truncated)
    memset(buffer, 0, size);

    // read
    off_t res1 = lseek(bd->fd,
-            (off_t)block*cfg->block_size + (off_t)off, SEEK_SET);
+            (off_t)block*bd->cfg->erase_size + (off_t)off, SEEK_SET);
    if (res1 < 0) {
        int err = -errno;
        LFS_FILEBD_TRACE("lfs_filebd_read -> %d", err);
@@ -102,14 +106,14 @@ int lfs_filebd_prog(const struct lfs_config *cfg, lfs_block_t block,
    lfs_filebd_t *bd = cfg->context;

    // check if write is valid
-    LFS_ASSERT(block < cfg->block_count);
-    LFS_ASSERT(off  % cfg->prog_size == 0);
-    LFS_ASSERT(size % cfg->prog_size == 0);
-    LFS_ASSERT(off+size <= cfg->block_size);
+    LFS_ASSERT(block < bd->cfg->erase_count);
+    LFS_ASSERT(off  % bd->cfg->prog_size == 0);
+    LFS_ASSERT(size % bd->cfg->prog_size == 0);
+    LFS_ASSERT(off+size <= bd->cfg->erase_size);

    // program data
    off_t res1 = lseek(bd->fd,
-            (off_t)block*cfg->block_size + (off_t)off, SEEK_SET);
+            (off_t)block*bd->cfg->erase_size + (off_t)off, SEEK_SET);
    if (res1 < 0) {
        int err = -errno;
        LFS_FILEBD_TRACE("lfs_filebd_prog -> %d", err);
@@ -129,10 +133,11 @@ int lfs_filebd_prog(const struct lfs_config *cfg, lfs_block_t block,

 int lfs_filebd_erase(const struct lfs_config *cfg, lfs_block_t block) {
    LFS_FILEBD_TRACE("lfs_filebd_erase(%p, 0x%"PRIx32" (%"PRIu32"))",
-            (void*)cfg, block, cfg->block_size);
+            (void*)cfg, block, ((lfs_file_t*)cfg->context)->cfg->erase_size);
+    lfs_filebd_t *bd = cfg->context;

    // check if erase is valid
-    LFS_ASSERT(block < cfg->block_count);
+    LFS_ASSERT(block < bd->cfg->erase_count);

    // erase is a noop
    (void)block;
--- a/bd/lfs_filebd.h
+++ b/bd/lfs_filebd.h
@@ -26,14 +26,31 @@ extern "C"
 #endif
 #endif

+// filebd config
+struct lfs_filebd_config {
+    // Minimum size of a read operation in bytes.
+    lfs_size_t read_size;
+
+    // Minimum size of a program operation in bytes.
+    lfs_size_t prog_size;
+
+    // Size of an erase operation in bytes.
+    lfs_size_t erase_size;
+
+    // Number of erase blocks on the device.
+    lfs_size_t erase_count;
+};
+
 // filebd state
 typedef struct lfs_filebd {
    int fd;
+    const struct lfs_filebd_config *cfg;
 } lfs_filebd_t;


-// Create a file block device using the geometry in lfs_config
-int lfs_filebd_create(const struct lfs_config *cfg, const char *path);
+// Create a file block device
+int lfs_filebd_create(const struct lfs_config *cfg, const char *path,
+        const struct lfs_filebd_config *bdcfg);

 // Clean up memory associated with block device
 int lfs_filebd_destroy(const struct lfs_config *cfg);
--- a/bd/lfs_rambd.c
+++ b/bd/lfs_rambd.c
@@ -7,18 +7,19 @@
 */
 #include "bd/lfs_rambd.h"

-int lfs_rambd_createcfg(const struct lfs_config *cfg,
+int lfs_rambd_create(const struct lfs_config *cfg,
        const struct lfs_rambd_config *bdcfg) {
-    LFS_RAMBD_TRACE("lfs_rambd_createcfg(%p {.context=%p, "
-                ".read=%p, .prog=%p, .erase=%p, .sync=%p, "
-                ".read_size=%"PRIu32", .prog_size=%"PRIu32", "
-                ".block_size=%"PRIu32", .block_count=%"PRIu32"}, "
-                "%p {.buffer=%p})",
+    LFS_RAMBD_TRACE("lfs_rambd_create(%p {.context=%p, "
+                ".read=%p, .prog=%p, .erase=%p, .sync=%p}, "
+                "%p {.read_size=%"PRIu32", .prog_size=%"PRIu32", "
+                ".erase_size=%"PRIu32", .erase_count=%"PRIu32", "
+                ".buffer=%p})",
            (void*)cfg, cfg->context,
            (void*)(uintptr_t)cfg->read, (void*)(uintptr_t)cfg->prog,
            (void*)(uintptr_t)cfg->erase, (void*)(uintptr_t)cfg->sync,
-            cfg->read_size, cfg->prog_size, cfg->block_size, cfg->block_count,
-            (void*)bdcfg, bdcfg->buffer);
+            (void*)bdcfg,
+            bdcfg->read_size, bdcfg->prog_size, bdcfg->erase_size,
+            bdcfg->erase_count, bdcfg->buffer);
    lfs_rambd_t *bd = cfg->context;
    bd->cfg = bdcfg;

@@ -26,35 +27,20 @@ int lfs_rambd_createcfg(const struct lfs_config *cfg,
    if (bd->cfg->buffer) {
        bd->buffer = bd->cfg->buffer;
    } else {
-        bd->buffer = lfs_malloc(cfg->block_size * cfg->block_count);
+        bd->buffer = lfs_malloc(bd->cfg->erase_size * bd->cfg->erase_count);
        if (!bd->buffer) {
-            LFS_RAMBD_TRACE("lfs_rambd_createcfg -> %d", LFS_ERR_NOMEM);
+            LFS_RAMBD_TRACE("lfs_rambd_create -> %d", LFS_ERR_NOMEM);
            return LFS_ERR_NOMEM;
        }
    }

    // zero for reproducibility
-    memset(bd->buffer, 0, cfg->block_size * cfg->block_count);
+    memset(bd->buffer, 0, bd->cfg->erase_size * bd->cfg->erase_count);

-    LFS_RAMBD_TRACE("lfs_rambd_createcfg -> %d", 0);
+    LFS_RAMBD_TRACE("lfs_rambd_create -> %d", 0);
    return 0;
 }

-int lfs_rambd_create(const struct lfs_config *cfg) {
-    LFS_RAMBD_TRACE("lfs_rambd_create(%p {.context=%p, "
-                ".read=%p, .prog=%p, .erase=%p, .sync=%p, "
-                ".read_size=%"PRIu32", .prog_size=%"PRIu32", "
-                ".block_size=%"PRIu32", .block_count=%"PRIu32"})",
-            (void*)cfg, cfg->context,
-            (void*)(uintptr_t)cfg->read, (void*)(uintptr_t)cfg->prog,
-            (void*)(uintptr_t)cfg->erase, (void*)(uintptr_t)cfg->sync,
-            cfg->read_size, cfg->prog_size, cfg->block_size, cfg->block_count);
-    static const struct lfs_rambd_config defaults = {0};
-    int err = lfs_rambd_createcfg(cfg, &defaults);
-    LFS_RAMBD_TRACE("lfs_rambd_create -> %d", err);
-    return err;
-}
-
 int lfs_rambd_destroy(const struct lfs_config *cfg) {
    LFS_RAMBD_TRACE("lfs_rambd_destroy(%p)", (void*)cfg);
    // clean up memory
@@ -74,13 +60,13 @@ int lfs_rambd_read(const struct lfs_config *cfg, lfs_block_t block,
    lfs_rambd_t *bd = cfg->context;

    // check if read is valid
-    LFS_ASSERT(block < cfg->block_count);
-    LFS_ASSERT(off  % cfg->read_size == 0);
-    LFS_ASSERT(size % cfg->read_size == 0);
-    LFS_ASSERT(off+size <= cfg->block_size);
+    LFS_ASSERT(block < bd->cfg->erase_count);
+    LFS_ASSERT(off  % bd->cfg->read_size == 0);
+    LFS_ASSERT(size % bd->cfg->read_size == 0);
+    LFS_ASSERT(off+size <= bd->cfg->erase_size);

    // read data
-    memcpy(buffer, &bd->buffer[block*cfg->block_size + off], size);
+    memcpy(buffer, &bd->buffer[block*bd->cfg->erase_size + off], size);

    LFS_RAMBD_TRACE("lfs_rambd_read -> %d", 0);
    return 0;
@@ -94,13 +80,13 @@ int lfs_rambd_prog(const struct lfs_config *cfg, lfs_block_t block,
    lfs_rambd_t *bd = cfg->context;

    // check if write is valid
-    LFS_ASSERT(block < cfg->block_count);
-    LFS_ASSERT(off  % cfg->prog_size == 0);
-    LFS_ASSERT(size % cfg->prog_size == 0);
-    LFS_ASSERT(off+size <= cfg->block_size);
+    LFS_ASSERT(block < bd->cfg->erase_count);
+    LFS_ASSERT(off  % bd->cfg->prog_size == 0);
+    LFS_ASSERT(size % bd->cfg->prog_size == 0);
+    LFS_ASSERT(off+size <= bd->cfg->erase_size);

    // program data
-    memcpy(&bd->buffer[block*cfg->block_size + off], buffer, size);
+    memcpy(&bd->buffer[block*bd->cfg->erase_size + off], buffer, size);

    LFS_RAMBD_TRACE("lfs_rambd_prog -> %d", 0);
    return 0;
@@ -108,10 +94,11 @@ int lfs_rambd_prog(const struct lfs_config *cfg, lfs_block_t block,

 int lfs_rambd_erase(const struct lfs_config *cfg, lfs_block_t block) {
    LFS_RAMBD_TRACE("lfs_rambd_erase(%p, 0x%"PRIx32" (%"PRIu32"))",
-            (void*)cfg, block, cfg->block_size);
+            (void*)cfg, block, ((lfs_rambd_t*)cfg->context)->cfg->erase_size);
+    lfs_rambd_t *bd = cfg->context;

    // check if erase is valid
-    LFS_ASSERT(block < cfg->block_count);
+    LFS_ASSERT(block < bd->cfg->erase_count);

    // erase is a noop
    (void)block;
--- a/bd/lfs_rambd.h
+++ b/bd/lfs_rambd.h
@@ -26,8 +26,20 @@ extern "C"
 #endif
 #endif

-// rambd config (optional)
+// rambd config
 struct lfs_rambd_config {
+    // Minimum size of a read operation in bytes.
+    lfs_size_t read_size;
+
+    // Minimum size of a program operation in bytes.
+    lfs_size_t prog_size;
+
+    // Size of an erase operation in bytes.
+    lfs_size_t erase_size;
+
+    // Number of erase blocks on the device.
+    lfs_size_t erase_count;
+
    // Optional statically allocated buffer for the block device.
    void *buffer;
 };
@@ -39,9 +51,8 @@ typedef struct lfs_rambd {
 } lfs_rambd_t;


-// Create a RAM block device using the geometry in lfs_config
-int lfs_rambd_create(const struct lfs_config *cfg);
-int lfs_rambd_createcfg(const struct lfs_config *cfg,
+// Create a RAM block device
+int lfs_rambd_create(const struct lfs_config *cfg,
        const struct lfs_rambd_config *bdcfg);

 // Clean up memory associated with block device
--- a/lfs.c
+++ b/lfs.c
--- a/lfs.h
+++ b/lfs.h
@@ -21,7 +21,7 @@ extern "C"
 // Software library version
 // Major (top-nibble), incremented on backwards incompatible changes
 // Minor (bottom-nibble), incremented on feature additions
-#define LFS_VERSION 0x00020006
+#define LFS_VERSION 0x00020009
 #define LFS_VERSION_MAJOR (0xffff & (LFS_VERSION >> 16))
 #define LFS_VERSION_MINOR (0xffff & (LFS_VERSION >>  0))

@@ -52,10 +52,8 @@ typedef uint32_t lfs_block_t;
 #endif

 // Maximum size of a file in bytes, may be redefined to limit to support other
-// drivers. Limited on disk to <= 4294967296. However, above 2147483647 the
-// functions lfs_file_seek, lfs_file_size, and lfs_file_tell will return
-// incorrect values due to using signed integers. Stored in superblock and
-// must be respected by other littlefs drivers.
+// drivers. Limited on disk to <= 2147483647. Stored in superblock and must be
+// respected by other littlefs drivers.
 #ifndef LFS_FILE_MAX
 #define LFS_FILE_MAX 2147483647
 #endif
@@ -226,9 +224,20 @@ struct lfs_config {
    // Size of the lookahead buffer in bytes. A larger lookahead buffer
    // increases the number of blocks found during an allocation pass. The
    // lookahead buffer is stored as a compact bitmap, so each byte of RAM
-    // can track 8 blocks. Must be a multiple of 8.
+    // can track 8 blocks.
    lfs_size_t lookahead_size;

+    // Threshold for metadata compaction during lfs_fs_gc in bytes. Metadata
+    // pairs that exceed this threshold will be compacted during lfs_fs_gc.
+    // Defaults to ~88% block_size when zero, though the default may change
+    // in the future.
+    //
+    // Note this only affects lfs_fs_gc. Normal compactions still only occur
+    // when full.
+    //
+    // Set to -1 to disable metadata compaction during lfs_fs_gc.
+    lfs_size_t compact_thresh;
+
    // Optional statically allocated read buffer. Must be cache_size.
    // By default lfs_malloc is used to allocate this buffer.
    void *read_buffer;
@@ -237,9 +246,8 @@ struct lfs_config {
    // By default lfs_malloc is used to allocate this buffer.
    void *prog_buffer;

-    // Optional statically allocated lookahead buffer. Must be lookahead_size
-    // and aligned to a 32-bit boundary. By default lfs_malloc is used to
-    // allocate this buffer.
+    // Optional statically allocated lookahead buffer. Must be lookahead_size.
+    // By default lfs_malloc is used to allocate this buffer.
    void *lookahead_buffer;

    // Optional upper limit on length of file names in bytes. No downside for
@@ -263,6 +271,23 @@ struct lfs_config {
    // can help bound the metadata compaction time. Must be <= block_size.
    // Defaults to block_size when zero.
    lfs_size_t metadata_max;
+
+    // Optional upper limit on inlined files in bytes. Inlined files live in
+    // metadata and decrease storage requirements, but may be limited to
+    // improve metadata-related performance. Must be <= cache_size, <=
+    // attr_max, and <= block_size/8. Defaults to the largest possible
+    // inline_max when zero.
+    //
+    // Set to -1 to disable inlined files.
+    lfs_size_t inline_max;
+
+#ifdef LFS_MULTIVERSION
+    // On-disk version to use when writing in the form of 16-bit major version
+    // + 16-bit minor version. This limiting metadata to what is supported by
+    // older minor versions. Note that some features will be lost. Defaults to 
+    // to the most recent minor version when zero.
+    uint32_t disk_version;
+#endif
 };

 // File info structure
@@ -280,6 +305,27 @@ struct lfs_info {
    char name[LFS_NAME_MAX+1];
 };

+// Filesystem info structure
+struct lfs_fsinfo {
+    // On-disk version.
+    uint32_t disk_version;
+
+    // Size of a logical block in bytes.
+    lfs_size_t block_size;
+
+    // Number of logical blocks in filesystem.
+    lfs_size_t block_count;
+
+    // Upper limit on the length of file names in bytes.
+    lfs_size_t name_max;
+
+    // Upper limit on the size of files in bytes.
+    lfs_size_t file_max;
+
+    // Upper limit on the size of custom attributes in bytes.
+    lfs_size_t attr_max;
+};
+
 // Custom attribute structure, used to describe custom attributes
 // committed atomically during file writes.
 struct lfs_attr {
@@ -401,18 +447,20 @@ typedef struct lfs {
    lfs_gstate_t gdisk;
    lfs_gstate_t gdelta;

-    struct lfs_free {
-        lfs_block_t off;
+    struct lfs_lookahead {
+        lfs_block_t start;
        lfs_block_t size;
-        lfs_block_t i;
-        lfs_block_t ack;
-        uint32_t *buffer;
-    } free;
+        lfs_block_t next;
+        lfs_block_t ckpoint;
+        uint8_t *buffer;
+    } lookahead;

    const struct lfs_config *cfg;
+    lfs_size_t block_count;
    lfs_size_t name_max;
    lfs_size_t file_max;
    lfs_size_t attr_max;
+    lfs_size_t inline_max;

 #ifdef LFS_MIGRATE
    struct lfs1 *lfs1;
@@ -659,6 +707,12 @@ int lfs_dir_rewind(lfs_t *lfs, lfs_dir_t *dir);

 /// Filesystem-level filesystem operations

+// Find on-disk info about the filesystem
+//
+// Fills out the fsinfo structure based on the filesystem found on-disk.
+// Returns a negative error code on failure.
+int lfs_fs_stat(lfs_t *lfs, struct lfs_fsinfo *fsinfo);
+
 // Finds the current size of the filesystem
 //
 // Note: Result is best effort. If files share COW structures, the returned
@@ -688,6 +742,34 @@ int lfs_fs_traverse(lfs_t *lfs, int (*cb)(void*, lfs_block_t), void *data);
 int lfs_fs_mkconsistent(lfs_t *lfs);
 #endif

+#ifndef LFS_READONLY
+// Attempt any janitorial work
+//
+// This currently:
+// 1. Calls mkconsistent if not already consistent
+// 2. Compacts metadata > compact_thresh
+// 3. Populates the block allocator
+//
+// Though additional janitorial work may be added in the future.
+//
+// Calling this function is not required, but may allow the offloading of
+// expensive janitorial work to a less time-critical code path.
+//
+// Returns a negative error code on failure. Accomplishing nothing is not
+// an error.
+int lfs_fs_gc(lfs_t *lfs);
+#endif
+
+#ifndef LFS_READONLY
+// Grows the filesystem to a new size, updating the superblock with the new
+// block count.
+//
+// Note: This is irreversible.
+//
+// Returns a negative error code on failure.
+int lfs_fs_grow(lfs_t *lfs, lfs_size_t block_count);
+#endif
+
 #ifndef LFS_READONLY
 #ifdef LFS_MIGRATE
 // Attempts to migrate a previous version of littlefs
--- a/lfs_util.c
+++ b/lfs_util.c
@@ -11,6 +11,8 @@
 #ifndef LFS_CONFIG


+// If user provides their own CRC impl we don't need this
+#ifndef LFS_CRC
 // Software CRC implementation with small lookup table
 uint32_t lfs_crc(uint32_t crc, const void *buffer, size_t size) {
    static const uint32_t rtable[16] = {
@@ -29,6 +31,7 @@ uint32_t lfs_crc(uint32_t crc, const void *buffer, size_t size) {

    return crc;
 }
+#endif


 #endif
--- a/lfs_util.h
+++ b/lfs_util.h
@@ -23,7 +23,6 @@
 // System includes
 #include <stdint.h>
 #include <stdbool.h>
-#include <sys/types.h>
 #include <string.h>
 #include <inttypes.h>

@@ -213,12 +212,22 @@ static inline uint32_t lfs_tobe32(uint32_t a) {
 }

 // Calculate CRC-32 with polynomial = 0x04c11db7
+#ifdef LFS_CRC
+uint32_t lfs_crc(uint32_t crc, const void *buffer, size_t size) {
+    return LFS_CRC(crc, buffer, size)
+}
+#else
 uint32_t lfs_crc(uint32_t crc, const void *buffer, size_t size);
+#endif

 // Allocate memory, only used if buffers are not provided to littlefs
-// Note, memory must be 64-bit aligned
+//
+// littlefs current has no alignment requirements, as it only allocates
+// byte-level buffers.
 static inline void *lfs_malloc(size_t size) {
-#ifndef LFS_NO_MALLOC
+#if defined(LFS_MALLOC)
+    return LFS_MALLOC(size);
+#elif !defined(LFS_NO_MALLOC)
    return malloc(size);
 #else
    (void)size;
@@ -228,7 +237,9 @@ static inline void *lfs_malloc(size_t size) {

 // Deallocate memory, only used if buffers are not provided to littlefs
 static inline void lfs_free(void *p) {
-#ifndef LFS_NO_MALLOC
+#if defined(LFS_FREE)
+    LFS_FREE(p);
+#elif !defined(LFS_NO_MALLOC)
    free(p);
 #else
    (void)p;
--- a/runners/bench_runner.c
+++ b/runners/bench_runner.c
@@ -1271,9 +1271,9 @@ static void list_geometries(void) {
                builtin_geometries[g].name,
                READ_SIZE,
                PROG_SIZE,
-                BLOCK_SIZE,
-                BLOCK_COUNT,
-                BLOCK_SIZE*BLOCK_COUNT);
+                ERASE_SIZE,
+                ERASE_COUNT,
+                ERASE_SIZE*ERASE_COUNT);
    }
 }

@@ -1321,9 +1321,15 @@ void perm_run(
        .block_cycles       = BLOCK_CYCLES,
        .cache_size         = CACHE_SIZE,
        .lookahead_size     = LOOKAHEAD_SIZE,
+        .compact_thresh     = COMPACT_THRESH,
+        .inline_max         = INLINE_MAX,
    };

    struct lfs_emubd_config bdcfg = {
+        .read_size          = READ_SIZE,
+        .prog_size          = PROG_SIZE,
+        .erase_size         = ERASE_SIZE,
+        .erase_count        = ERASE_COUNT,
        .erase_value        = ERASE_VALUE,
        .erase_cycles       = ERASE_CYCLES,
        .badblock_behavior  = BADBLOCK_BEHAVIOR,
@@ -1333,7 +1339,7 @@ void perm_run(
        .erase_sleep        = bench_erase_sleep,
    };

-    int err = lfs_emubd_createcfg(&cfg, bench_disk_path, &bdcfg);
+    int err = lfs_emubd_create(&cfg, &bdcfg);
    if (err) {
        fprintf(stderr, "error: could not create block device: %d\n", err);
        exit(-1);
@@ -1761,19 +1767,19 @@ invalid_define:
                                    = BENCH_LIT(sizes[0]);
                            geometry->defines[PROG_SIZE_i]
                                    = BENCH_LIT(sizes[1]);
-                            geometry->defines[BLOCK_SIZE_i]
+                            geometry->defines[ERASE_SIZE_i]
                                    = BENCH_LIT(sizes[2]);
                        } else if (count >= 2) {
                            geometry->defines[PROG_SIZE_i]
                                    = BENCH_LIT(sizes[0]);
-                            geometry->defines[BLOCK_SIZE_i]
+                            geometry->defines[ERASE_SIZE_i]
                                    = BENCH_LIT(sizes[1]);
                        } else {
-                            geometry->defines[BLOCK_SIZE_i]
+                            geometry->defines[ERASE_SIZE_i]
                                    = BENCH_LIT(sizes[0]);
                        }
                        if (count >= 4) {
-                            geometry->defines[BLOCK_COUNT_i]
+                            geometry->defines[ERASE_COUNT_i]
                                    = BENCH_LIT(sizes[3]);
                        }
                        optarg = s;
@@ -1805,19 +1811,19 @@ invalid_define:
                                    = BENCH_LIT(sizes[0]);
                            geometry->defines[PROG_SIZE_i]
                                    = BENCH_LIT(sizes[1]);
-                            geometry->defines[BLOCK_SIZE_i]
+                            geometry->defines[ERASE_SIZE_i]
                                    = BENCH_LIT(sizes[2]);
                        } else if (count >= 2) {
                            geometry->defines[PROG_SIZE_i]
                                    = BENCH_LIT(sizes[0]);
-                            geometry->defines[BLOCK_SIZE_i]
+                            geometry->defines[ERASE_SIZE_i]
                                    = BENCH_LIT(sizes[1]);
                        } else {
-                            geometry->defines[BLOCK_SIZE_i]
+                            geometry->defines[ERASE_SIZE_i]
                                    = BENCH_LIT(sizes[0]);
                        }
                        if (count >= 4) {
-                            geometry->defines[BLOCK_COUNT_i]
+                            geometry->defines[ERASE_COUNT_i]
                                    = BENCH_LIT(sizes[3]);
                        }
                        optarg = s;
--- a/runners/bench_runner.h
+++ b/runners/bench_runner.h
@@ -89,22 +89,30 @@ intmax_t bench_define(size_t define);
 
 #define READ_SIZE_i          0
 #define PROG_SIZE_i          1
-#define BLOCK_SIZE_i         2
-#define BLOCK_COUNT_i        3
-#define CACHE_SIZE_i         4
-#define LOOKAHEAD_SIZE_i     5
-#define BLOCK_CYCLES_i       6
-#define ERASE_VALUE_i        7
-#define ERASE_CYCLES_i       8
-#define BADBLOCK_BEHAVIOR_i  9
-#define POWERLOSS_BEHAVIOR_i 10
+#define ERASE_SIZE_i         2
+#define ERASE_COUNT_i        3
+#define BLOCK_SIZE_i         4
+#define BLOCK_COUNT_i        5
+#define CACHE_SIZE_i         6
+#define LOOKAHEAD_SIZE_i     7
+#define COMPACT_THRESH_i     8
+#define INLINE_MAX_i         9
+#define BLOCK_CYCLES_i       10
+#define ERASE_VALUE_i        11
+#define ERASE_CYCLES_i       12
+#define BADBLOCK_BEHAVIOR_i  13
+#define POWERLOSS_BEHAVIOR_i 14

 #define READ_SIZE           bench_define(READ_SIZE_i)
 #define PROG_SIZE           bench_define(PROG_SIZE_i)
+#define ERASE_SIZE          bench_define(ERASE_SIZE_i)
+#define ERASE_COUNT         bench_define(ERASE_COUNT_i)
 #define BLOCK_SIZE          bench_define(BLOCK_SIZE_i)
 #define BLOCK_COUNT         bench_define(BLOCK_COUNT_i)
 #define CACHE_SIZE          bench_define(CACHE_SIZE_i)
 #define LOOKAHEAD_SIZE      bench_define(LOOKAHEAD_SIZE_i)
+#define COMPACT_THRESH      bench_define(COMPACT_THRESH_i)
+#define INLINE_MAX          bench_define(INLINE_MAX_i)
 #define BLOCK_CYCLES        bench_define(BLOCK_CYCLES_i)
 #define ERASE_VALUE         bench_define(ERASE_VALUE_i)
 #define ERASE_CYCLES        bench_define(ERASE_CYCLES_i)
@@ -113,11 +121,15 @@ intmax_t bench_define(size_t define);

 #define BENCH_IMPLICIT_DEFINES \
    BENCH_DEF(READ_SIZE,          PROG_SIZE) \
-    BENCH_DEF(PROG_SIZE,          BLOCK_SIZE) \
-    BENCH_DEF(BLOCK_SIZE,         0) \
-    BENCH_DEF(BLOCK_COUNT,        (1024*1024)/BLOCK_SIZE) \
+    BENCH_DEF(PROG_SIZE,          ERASE_SIZE) \
+    BENCH_DEF(ERASE_SIZE,         0) \
+    BENCH_DEF(ERASE_COUNT,        (1024*1024)/BLOCK_SIZE) \
+    BENCH_DEF(BLOCK_SIZE,         ERASE_SIZE) \
+    BENCH_DEF(BLOCK_COUNT,        ERASE_COUNT/lfs_max(BLOCK_SIZE/ERASE_SIZE,1))\
    BENCH_DEF(CACHE_SIZE,         lfs_max(64,lfs_max(READ_SIZE,PROG_SIZE))) \
    BENCH_DEF(LOOKAHEAD_SIZE,     16) \
+    BENCH_DEF(COMPACT_THRESH,     0) \
+    BENCH_DEF(INLINE_MAX,         0) \
    BENCH_DEF(BLOCK_CYCLES,       -1) \
    BENCH_DEF(ERASE_VALUE,        0xff) \
    BENCH_DEF(ERASE_CYCLES,       0) \
@@ -125,7 +137,7 @@ intmax_t bench_define(size_t define);
    BENCH_DEF(POWERLOSS_BEHAVIOR, LFS_EMUBD_POWERLOSS_NOOP)

 #define BENCH_GEOMETRY_DEFINE_COUNT 4
-#define BENCH_IMPLICIT_DEFINE_COUNT 11
+#define BENCH_IMPLICIT_DEFINE_COUNT 15


 #endif
--- a/runners/test_runner.c
+++ b/runners/test_runner.c
@@ -1312,9 +1312,9 @@ static void list_geometries(void) {
                builtin_geometries[g].name,
                READ_SIZE,
                PROG_SIZE,
-                BLOCK_SIZE,
-                BLOCK_COUNT,
-                BLOCK_SIZE*BLOCK_COUNT);
+                ERASE_SIZE,
+                ERASE_COUNT,
+                ERASE_SIZE*ERASE_COUNT);
    }
 }

@@ -1346,9 +1346,18 @@ static void run_powerloss_none(
        .block_cycles       = BLOCK_CYCLES,
        .cache_size         = CACHE_SIZE,
        .lookahead_size     = LOOKAHEAD_SIZE,
+        .compact_thresh     = COMPACT_THRESH,
+        .inline_max         = INLINE_MAX,
+    #ifdef LFS_MULTIVERSION
+        .disk_version       = DISK_VERSION,
+    #endif
    };

    struct lfs_emubd_config bdcfg = {
+        .read_size          = READ_SIZE,
+        .prog_size          = PROG_SIZE,
+        .erase_size         = ERASE_SIZE,
+        .erase_count        = ERASE_COUNT,
        .erase_value        = ERASE_VALUE,
        .erase_cycles       = ERASE_CYCLES,
        .badblock_behavior  = BADBLOCK_BEHAVIOR,
@@ -1358,7 +1367,7 @@ static void run_powerloss_none(
        .erase_sleep        = test_erase_sleep,
    };

-    int err = lfs_emubd_createcfg(&cfg, test_disk_path, &bdcfg);
+    int err = lfs_emubd_create(&cfg, &bdcfg);
    if (err) {
        fprintf(stderr, "error: could not create block device: %d\n", err);
        exit(-1);
@@ -1415,9 +1424,18 @@ static void run_powerloss_linear(
        .block_cycles       = BLOCK_CYCLES,
        .cache_size         = CACHE_SIZE,
        .lookahead_size     = LOOKAHEAD_SIZE,
+        .compact_thresh     = COMPACT_THRESH,
+        .inline_max         = INLINE_MAX,
+    #ifdef LFS_MULTIVERSION
+        .disk_version       = DISK_VERSION,
+    #endif
    };

    struct lfs_emubd_config bdcfg = {
+        .read_size          = READ_SIZE,
+        .prog_size          = PROG_SIZE,
+        .erase_size         = ERASE_SIZE,
+        .erase_count        = ERASE_COUNT,
        .erase_value        = ERASE_VALUE,
        .erase_cycles       = ERASE_CYCLES,
        .badblock_behavior  = BADBLOCK_BEHAVIOR,
@@ -1431,7 +1449,7 @@ static void run_powerloss_linear(
        .powerloss_data     = &powerloss_jmp,
    };

-    int err = lfs_emubd_createcfg(&cfg, test_disk_path, &bdcfg);
+    int err = lfs_emubd_create(&cfg, &bdcfg);
    if (err) {
        fprintf(stderr, "error: could not create block device: %d\n", err);
        exit(-1);
@@ -1501,9 +1519,18 @@ static void run_powerloss_log(
        .block_cycles       = BLOCK_CYCLES,
        .cache_size         = CACHE_SIZE,
        .lookahead_size     = LOOKAHEAD_SIZE,
+        .compact_thresh     = COMPACT_THRESH,
+        .inline_max         = INLINE_MAX,
+    #ifdef LFS_MULTIVERSION
+        .disk_version       = DISK_VERSION,
+    #endif
    };

    struct lfs_emubd_config bdcfg = {
+        .read_size          = READ_SIZE,
+        .prog_size          = PROG_SIZE,
+        .erase_size         = ERASE_SIZE,
+        .erase_count        = ERASE_COUNT,
        .erase_value        = ERASE_VALUE,
        .erase_cycles       = ERASE_CYCLES,
        .badblock_behavior  = BADBLOCK_BEHAVIOR,
@@ -1517,7 +1544,7 @@ static void run_powerloss_log(
        .powerloss_data     = &powerloss_jmp,
    };

-    int err = lfs_emubd_createcfg(&cfg, test_disk_path, &bdcfg);
+    int err = lfs_emubd_create(&cfg, &bdcfg);
    if (err) {
        fprintf(stderr, "error: could not create block device: %d\n", err);
        exit(-1);
@@ -1585,9 +1612,18 @@ static void run_powerloss_cycles(
        .block_cycles       = BLOCK_CYCLES,
        .cache_size         = CACHE_SIZE,
        .lookahead_size     = LOOKAHEAD_SIZE,
+        .compact_thresh     = COMPACT_THRESH,
+        .inline_max         = INLINE_MAX,
+    #ifdef LFS_MULTIVERSION
+        .disk_version       = DISK_VERSION,
+    #endif
    };

    struct lfs_emubd_config bdcfg = {
+        .read_size          = READ_SIZE,
+        .prog_size          = PROG_SIZE,
+        .erase_size         = ERASE_SIZE,
+        .erase_count        = ERASE_COUNT,
        .erase_value        = ERASE_VALUE,
        .erase_cycles       = ERASE_CYCLES,
        .badblock_behavior  = BADBLOCK_BEHAVIOR,
@@ -1601,7 +1637,7 @@ static void run_powerloss_cycles(
        .powerloss_data     = &powerloss_jmp,
    };

-    int err = lfs_emubd_createcfg(&cfg, test_disk_path, &bdcfg);
+    int err = lfs_emubd_create(&cfg, &bdcfg);
    if (err) {
        fprintf(stderr, "error: could not create block device: %d\n", err);
        exit(-1);
@@ -1767,9 +1803,18 @@ static void run_powerloss_exhaustive(
        .block_cycles       = BLOCK_CYCLES,
        .cache_size         = CACHE_SIZE,
        .lookahead_size     = LOOKAHEAD_SIZE,
+        .compact_thresh     = COMPACT_THRESH,
+        .inline_max         = INLINE_MAX,
+    #ifdef LFS_MULTIVERSION
+        .disk_version       = DISK_VERSION,
+    #endif
    };

    struct lfs_emubd_config bdcfg = {
+        .read_size          = READ_SIZE,
+        .prog_size          = PROG_SIZE,
+        .erase_size         = ERASE_SIZE,
+        .erase_count        = ERASE_COUNT,
        .erase_value        = ERASE_VALUE,
        .erase_cycles       = ERASE_CYCLES,
        .badblock_behavior  = BADBLOCK_BEHAVIOR,
@@ -1782,7 +1827,7 @@ static void run_powerloss_exhaustive(
        .powerloss_data     = NULL,
    };

-    int err = lfs_emubd_createcfg(&cfg, test_disk_path, &bdcfg);
+    int err = lfs_emubd_create(&cfg, &bdcfg);
    if (err) {
        fprintf(stderr, "error: could not create block device: %d\n", err);
        exit(-1);
@@ -2299,19 +2344,19 @@ invalid_define:
                                    = TEST_LIT(sizes[0]);
                            geometry->defines[PROG_SIZE_i]
                                    = TEST_LIT(sizes[1]);
-                            geometry->defines[BLOCK_SIZE_i]
+                            geometry->defines[ERASE_SIZE_i]
                                    = TEST_LIT(sizes[2]);
                        } else if (count >= 2) {
                            geometry->defines[PROG_SIZE_i]
                                    = TEST_LIT(sizes[0]);
-                            geometry->defines[BLOCK_SIZE_i]
+                            geometry->defines[ERASE_SIZE_i]
                                    = TEST_LIT(sizes[1]);
                        } else {
-                            geometry->defines[BLOCK_SIZE_i]
+                            geometry->defines[ERASE_SIZE_i]
                                    = TEST_LIT(sizes[0]);
                        }
                        if (count >= 4) {
-                            geometry->defines[BLOCK_COUNT_i]
+                            geometry->defines[ERASE_COUNT_i]
                                    = TEST_LIT(sizes[3]);
                        }
                        optarg = s;
@@ -2343,19 +2388,19 @@ invalid_define:
                                    = TEST_LIT(sizes[0]);
                            geometry->defines[PROG_SIZE_i]
                                    = TEST_LIT(sizes[1]);
-                            geometry->defines[BLOCK_SIZE_i]
+                            geometry->defines[ERASE_SIZE_i]
                                    = TEST_LIT(sizes[2]);
                        } else if (count >= 2) {
                            geometry->defines[PROG_SIZE_i]
                                    = TEST_LIT(sizes[0]);
-                            geometry->defines[BLOCK_SIZE_i]
+                            geometry->defines[ERASE_SIZE_i]
                                    = TEST_LIT(sizes[1]);
                        } else {
-                            geometry->defines[BLOCK_SIZE_i]
+                            geometry->defines[ERASE_SIZE_i]
                                    = TEST_LIT(sizes[0]);
                        }
                        if (count >= 4) {
-                            geometry->defines[BLOCK_COUNT_i]
+                            geometry->defines[ERASE_COUNT_i]
                                    = TEST_LIT(sizes[3]);
                        }
                        optarg = s;
--- a/runners/test_runner.h
+++ b/runners/test_runner.h
@@ -82,43 +82,58 @@ intmax_t test_define(size_t define);
 
 #define READ_SIZE_i          0
 #define PROG_SIZE_i          1
-#define BLOCK_SIZE_i         2
-#define BLOCK_COUNT_i        3
-#define CACHE_SIZE_i         4
-#define LOOKAHEAD_SIZE_i     5
-#define BLOCK_CYCLES_i       6
-#define ERASE_VALUE_i        7
-#define ERASE_CYCLES_i       8
-#define BADBLOCK_BEHAVIOR_i  9
-#define POWERLOSS_BEHAVIOR_i 10
+#define ERASE_SIZE_i         2
+#define ERASE_COUNT_i        3
+#define BLOCK_SIZE_i         4
+#define BLOCK_COUNT_i        5
+#define CACHE_SIZE_i         6
+#define LOOKAHEAD_SIZE_i     7
+#define COMPACT_THRESH_i     8
+#define INLINE_MAX_i         9
+#define BLOCK_CYCLES_i       10
+#define ERASE_VALUE_i        11
+#define ERASE_CYCLES_i       12
+#define BADBLOCK_BEHAVIOR_i  13
+#define POWERLOSS_BEHAVIOR_i 14
+#define DISK_VERSION_i       15

 #define READ_SIZE           TEST_DEFINE(READ_SIZE_i)
 #define PROG_SIZE           TEST_DEFINE(PROG_SIZE_i)
+#define ERASE_SIZE          TEST_DEFINE(ERASE_SIZE_i)
+#define ERASE_COUNT         TEST_DEFINE(ERASE_COUNT_i)
 #define BLOCK_SIZE          TEST_DEFINE(BLOCK_SIZE_i)
 #define BLOCK_COUNT         TEST_DEFINE(BLOCK_COUNT_i)
 #define CACHE_SIZE          TEST_DEFINE(CACHE_SIZE_i)
 #define LOOKAHEAD_SIZE      TEST_DEFINE(LOOKAHEAD_SIZE_i)
+#define COMPACT_THRESH      TEST_DEFINE(COMPACT_THRESH_i)
+#define INLINE_MAX          TEST_DEFINE(INLINE_MAX_i)
 #define BLOCK_CYCLES        TEST_DEFINE(BLOCK_CYCLES_i)
 #define ERASE_VALUE         TEST_DEFINE(ERASE_VALUE_i)
 #define ERASE_CYCLES        TEST_DEFINE(ERASE_CYCLES_i)
 #define BADBLOCK_BEHAVIOR   TEST_DEFINE(BADBLOCK_BEHAVIOR_i)
 #define POWERLOSS_BEHAVIOR  TEST_DEFINE(POWERLOSS_BEHAVIOR_i)
+#define DISK_VERSION        TEST_DEFINE(DISK_VERSION_i)

 #define TEST_IMPLICIT_DEFINES \
    TEST_DEF(READ_SIZE,          PROG_SIZE) \
-    TEST_DEF(PROG_SIZE,          BLOCK_SIZE) \
-    TEST_DEF(BLOCK_SIZE,         0) \
-    TEST_DEF(BLOCK_COUNT,        (1024*1024)/BLOCK_SIZE) \
+    TEST_DEF(PROG_SIZE,          ERASE_SIZE) \
+    TEST_DEF(ERASE_SIZE,         0) \
+    TEST_DEF(ERASE_COUNT,        (1024*1024)/ERASE_SIZE) \
+    TEST_DEF(BLOCK_SIZE,         ERASE_SIZE) \
+    TEST_DEF(BLOCK_COUNT,        ERASE_COUNT/lfs_max(BLOCK_SIZE/ERASE_SIZE,1)) \
    TEST_DEF(CACHE_SIZE,         lfs_max(64,lfs_max(READ_SIZE,PROG_SIZE))) \
    TEST_DEF(LOOKAHEAD_SIZE,     16) \
+    TEST_DEF(COMPACT_THRESH,     0) \
+    TEST_DEF(INLINE_MAX,         0) \
    TEST_DEF(BLOCK_CYCLES,       -1) \
    TEST_DEF(ERASE_VALUE,        0xff) \
    TEST_DEF(ERASE_CYCLES,       0) \
    TEST_DEF(BADBLOCK_BEHAVIOR,  LFS_EMUBD_BADBLOCK_PROGERROR) \
-    TEST_DEF(POWERLOSS_BEHAVIOR, LFS_EMUBD_POWERLOSS_NOOP)
+    TEST_DEF(POWERLOSS_BEHAVIOR, LFS_EMUBD_POWERLOSS_NOOP) \
+    TEST_DEF(DISK_VERSION,       0)

-#define TEST_IMPLICIT_DEFINE_COUNT 11
 #define TEST_GEOMETRY_DEFINE_COUNT 4
+#define TEST_IMPLICIT_DEFINE_COUNT 16


 #endif
--- a/tests/test_alloc.toml
+++ b/tests/test_alloc.toml
@@ -6,6 +6,8 @@ if = 'BLOCK_CYCLES == -1'
 [cases.test_alloc_parallel]
 defines.FILES = 3
 defines.SIZE = '(((BLOCK_SIZE-8)*(BLOCK_COUNT-6)) / FILES)'
+defines.GC = [false, true]
+defines.COMPACT_THRESH = ['-1', '0', 'BLOCK_SIZE/2']
 code = '''
    const char *names[] = {"bacon", "eggs", "pancakes"};
    lfs_file_t files[FILES];
@@ -24,6 +26,9 @@ code = '''
                LFS_O_WRONLY | LFS_O_CREAT | LFS_O_APPEND) => 0;
    }
    for (int n = 0; n < FILES; n++) {
+        if (GC) {
+            lfs_fs_gc(&lfs) => 0;
+        }
        size_t size = strlen(names[n]);
        for (lfs_size_t i = 0; i < SIZE; i += size) {
            lfs_file_write(&lfs, &files[n], names[n], size) => size;
@@ -55,6 +60,8 @@ code = '''
 [cases.test_alloc_serial]
 defines.FILES = 3
 defines.SIZE = '(((BLOCK_SIZE-8)*(BLOCK_COUNT-6)) / FILES)'
+defines.GC = [false, true]
+defines.COMPACT_THRESH = ['-1', '0', 'BLOCK_SIZE/2']
 code = '''
    const char *names[] = {"bacon", "eggs", "pancakes"};

@@ -75,6 +82,9 @@ code = '''
        uint8_t buffer[1024];
        memcpy(buffer, names[n], size);
        for (int i = 0; i < SIZE; i += size) {
+            if (GC) {
+                lfs_fs_gc(&lfs) => 0;
+            }
            lfs_file_write(&lfs, &file, buffer, size) => size;
        }
        lfs_file_close(&lfs, &file) => 0;
@@ -247,6 +257,9 @@ code = '''
    }
    res => LFS_ERR_NOSPC;

+    // note that lfs_fs_gc should not error here
+    lfs_fs_gc(&lfs) => 0;
+
    lfs_file_close(&lfs, &file) => 0;
    lfs_unmount(&lfs) => 0;

@@ -298,6 +311,9 @@ code = '''
    }
    res => LFS_ERR_NOSPC;

+    // note that lfs_fs_gc should not error here
+    lfs_fs_gc(&lfs) => 0;
+
    lfs_file_close(&lfs, &file) => 0;
    lfs_unmount(&lfs) => 0;

@@ -337,6 +353,8 @@ code = '''
        count += 1;
    }
    err => LFS_ERR_NOSPC;
+    // note that lfs_fs_gc should not error here
+    lfs_fs_gc(&lfs) => 0;
    lfs_file_close(&lfs, &file) => 0;

    lfs_remove(&lfs, "exhaustion") => 0;
@@ -435,6 +453,8 @@ code = '''
            break;
        }
    }
+    // note that lfs_fs_gc should not error here
+    lfs_fs_gc(&lfs) => 0;
    lfs_file_close(&lfs, &file) => 0;

    lfs_unmount(&lfs) => 0;
@@ -460,8 +480,8 @@ code = '''

 # chained dir exhaustion test
 [cases.test_alloc_chained_dir_exhaustion]
-if = 'BLOCK_SIZE == 512'
-defines.BLOCK_COUNT = 1024
+if = 'ERASE_SIZE == 512'
+defines.ERASE_COUNT = 1024
 code = '''
    lfs_t lfs;
    lfs_format(&lfs, cfg) => 0;
@@ -538,8 +558,8 @@ code = '''

 # split dir test
 [cases.test_alloc_split_dir]
-if = 'BLOCK_SIZE == 512'
-defines.BLOCK_COUNT = 1024
+if = 'ERASE_SIZE == 512'
+defines.ERASE_COUNT = 1024
 code = '''
    lfs_t lfs;
    lfs_format(&lfs, cfg) => 0;
@@ -587,8 +607,8 @@ code = '''

 # outdated lookahead test
 [cases.test_alloc_outdated_lookahead]
-if = 'BLOCK_SIZE == 512'
-defines.BLOCK_COUNT = 1024
+if = 'ERASE_SIZE == 512'
+defines.ERASE_COUNT = 1024
 code = '''
    lfs_t lfs;
    lfs_format(&lfs, cfg) => 0;
@@ -655,8 +675,8 @@ code = '''

 # outdated lookahead and split dir test
 [cases.test_alloc_outdated_lookahead_split_dir]
-if = 'BLOCK_SIZE == 512'
-defines.BLOCK_COUNT = 1024
+if = 'ERASE_SIZE == 512'
+defines.ERASE_COUNT = 1024
 code = '''
    lfs_t lfs;
    lfs_format(&lfs, cfg) => 0;
--- a/tests/test_badblocks.toml
+++ b/tests/test_badblocks.toml
@@ -2,7 +2,7 @@
 if = '(int32_t)BLOCK_CYCLES == -1'

 [cases.test_badblocks_single]
-defines.BLOCK_COUNT = 256 # small bd so test runs faster
+defines.ERASE_COUNT = 256 # small bd so test runs faster
 defines.ERASE_CYCLES = 0xffffffff
 defines.ERASE_VALUE = [0x00, 0xff, -1]
 defines.BADBLOCK_BEHAVIOR = [
@@ -82,7 +82,7 @@ code = '''
 '''

 [cases.test_badblocks_region_corruption] # (causes cascading failures)
-defines.BLOCK_COUNT = 256 # small bd so test runs faster
+defines.ERASE_COUNT = 256 # small bd so test runs faster
 defines.ERASE_CYCLES = 0xffffffff
 defines.ERASE_VALUE = [0x00, 0xff, -1]
 defines.BADBLOCK_BEHAVIOR = [
@@ -161,7 +161,7 @@ code = '''
 '''

 [cases.test_badblocks_alternating_corruption] # (causes cascading failures)
-defines.BLOCK_COUNT = 256 # small bd so test runs faster
+defines.ERASE_COUNT = 256 # small bd so test runs faster
 defines.ERASE_CYCLES = 0xffffffff
 defines.ERASE_VALUE = [0x00, 0xff, -1]
 defines.BADBLOCK_BEHAVIOR = [
--- a/tests/test_compat.toml
+++ b/tests/test_compat.toml
@@ -22,14 +22,16 @@ code = '''
 #define STRINGIZE_(x) #x
 #include STRINGIZE(LFSP)
 #else
-#define LFSP_VERSION LFS_VERSION
-#define LFSP_VERSION_MAJOR LFS_VERSION_MAJOR
-#define LFSP_VERSION_MINOR LFS_VERSION_MINOR
+#define LFSP_DISK_VERSION LFS_DISK_VERSION
+#define LFSP_DISK_VERSION_MAJOR LFS_DISK_VERSION_MAJOR
+#define LFSP_DISK_VERSION_MINOR LFS_DISK_VERSION_MINOR
 #define lfsp_t lfs_t
 #define lfsp_config lfs_config
 #define lfsp_format lfs_format
 #define lfsp_mount lfs_mount
 #define lfsp_unmount lfs_unmount
+#define lfsp_fsinfo lfs_fsinfo
+#define lfsp_fs_stat lfs_fs_stat
 #define lfsp_dir_t lfs_dir_t
 #define lfsp_info lfs_info
 #define LFSP_TYPE_REG LFS_TYPE_REG
@@ -58,7 +60,10 @@ code = '''

 # test we can mount in a new version
 [cases.test_compat_forward_mount]
-if = 'LFS_VERSION_MAJOR == LFSP_VERSION_MAJOR'
+if = '''
+    LFS_DISK_VERSION_MAJOR == LFSP_DISK_VERSION_MAJOR
+        && DISK_VERSION == 0
+'''
 code = '''
    // create the previous version
    struct lfsp_config cfgp;
@@ -74,13 +79,22 @@ code = '''
    // now test the new mount
    lfs_t lfs;
    lfs_mount(&lfs, cfg) => 0;
+
+    // we should be able to read the version using lfs_fs_stat
+    struct lfs_fsinfo fsinfo;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.disk_version == LFSP_DISK_VERSION);
+
    lfs_unmount(&lfs) => 0;
 '''

 # test we can read dirs in a new version
 [cases.test_compat_forward_read_dirs]
 defines.COUNT = 5
-if = 'LFS_VERSION_MAJOR == LFSP_VERSION_MAJOR'
+if = '''
+    LFS_DISK_VERSION_MAJOR == LFSP_DISK_VERSION_MAJOR
+        && DISK_VERSION == 0
+'''
 code = '''
    // create the previous version
    struct lfsp_config cfgp;
@@ -102,6 +116,11 @@ code = '''
    lfs_t lfs;
    lfs_mount(&lfs, cfg) => 0;

+    // we should be able to read the version using lfs_fs_stat
+    struct lfs_fsinfo fsinfo;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.disk_version == LFSP_DISK_VERSION);
+
    // can we list the directories?
    lfs_dir_t dir;
    lfs_dir_open(&lfs, &dir, "/") => 0;
@@ -132,7 +151,10 @@ code = '''
 defines.COUNT = 5
 defines.SIZE = [4, 32, 512, 8192]
 defines.CHUNK = 4
-if = 'LFS_VERSION_MAJOR == LFSP_VERSION_MAJOR'
+if = '''
+    LFS_DISK_VERSION_MAJOR == LFSP_DISK_VERSION_MAJOR
+        && DISK_VERSION == 0
+'''
 code = '''
    // create the previous version
    struct lfsp_config cfgp;
@@ -166,6 +188,11 @@ code = '''
    lfs_t lfs;
    lfs_mount(&lfs, cfg) => 0;

+    // we should be able to read the version using lfs_fs_stat
+    struct lfs_fsinfo fsinfo;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.disk_version == LFSP_DISK_VERSION);
+
    // can we list the files?
    lfs_dir_t dir;
    lfs_dir_open(&lfs, &dir, "/") => 0;
@@ -214,7 +241,10 @@ code = '''
 defines.COUNT = 5
 defines.SIZE = [4, 32, 512, 8192]
 defines.CHUNK = 4
-if = 'LFS_VERSION_MAJOR == LFSP_VERSION_MAJOR'
+if = '''
+    LFS_DISK_VERSION_MAJOR == LFSP_DISK_VERSION_MAJOR
+        && DISK_VERSION == 0
+'''
 code = '''
    // create the previous version
    struct lfsp_config cfgp;
@@ -251,6 +281,11 @@ code = '''
    lfs_t lfs;
    lfs_mount(&lfs, cfg) => 0;

+    // we should be able to read the version using lfs_fs_stat
+    struct lfs_fsinfo fsinfo;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.disk_version == LFSP_DISK_VERSION);
+
    // can we list the directories?
    lfs_dir_t dir;
    lfs_dir_open(&lfs, &dir, "/") => 0;
@@ -321,7 +356,10 @@ code = '''
 # test we can write dirs in a new version
 [cases.test_compat_forward_write_dirs]
 defines.COUNT = 10
-if = 'LFS_VERSION_MAJOR == LFSP_VERSION_MAJOR'
+if = '''
+    LFS_DISK_VERSION_MAJOR == LFSP_DISK_VERSION_MAJOR
+        && DISK_VERSION == 0
+'''
 code = '''
    // create the previous version
    struct lfsp_config cfgp;
@@ -343,6 +381,11 @@ code = '''
    lfs_t lfs;
    lfs_mount(&lfs, cfg) => 0;

+    // we should be able to read the version using lfs_fs_stat
+    struct lfs_fsinfo fsinfo;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.disk_version == LFSP_DISK_VERSION);
+
    // write another COUNT/2 dirs
    for (lfs_size_t i = COUNT/2; i < COUNT; i++) {
        char name[8];
@@ -380,7 +423,10 @@ code = '''
 defines.COUNT = 5
 defines.SIZE = [4, 32, 512, 8192]
 defines.CHUNK = 2
-if = 'LFS_VERSION_MAJOR == LFSP_VERSION_MAJOR'
+if = '''
+    LFS_DISK_VERSION_MAJOR == LFSP_DISK_VERSION_MAJOR
+        && DISK_VERSION == 0
+'''
 code = '''
    // create the previous version
    struct lfsp_config cfgp;
@@ -420,6 +466,11 @@ code = '''
    lfs_t lfs;
    lfs_mount(&lfs, cfg) => 0;

+    // we should be able to read the version using lfs_fs_stat
+    struct lfs_fsinfo fsinfo;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.disk_version == LFSP_DISK_VERSION);
+
    // write half COUNT files
    prng = 42;
    for (lfs_size_t i = 0; i < COUNT; i++) {
@@ -494,7 +545,10 @@ code = '''
 defines.COUNT = 5
 defines.SIZE = [4, 32, 512, 8192]
 defines.CHUNK = 2
-if = 'LFS_VERSION_MAJOR == LFSP_VERSION_MAJOR'
+if = '''
+    LFS_DISK_VERSION_MAJOR == LFSP_DISK_VERSION_MAJOR
+        && DISK_VERSION == 0
+'''
 code = '''
    // create the previous version
    struct lfsp_config cfgp;
@@ -537,6 +591,11 @@ code = '''
    lfs_t lfs;
    lfs_mount(&lfs, cfg) => 0;

+    // we should be able to read the version using lfs_fs_stat
+    struct lfs_fsinfo fsinfo;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.disk_version == LFSP_DISK_VERSION);
+
    // write half COUNT files
    prng = 42;
    for (lfs_size_t i = 0; i < COUNT; i++) {
@@ -636,7 +695,10 @@ code = '''

 # test we can mount in an old version
 [cases.test_compat_backward_mount]
-if = 'LFS_VERSION == LFSP_VERSION'
+if = '''
+    LFS_DISK_VERSION == LFSP_DISK_VERSION
+        && DISK_VERSION == 0
+'''
 code = '''
    // create the new version
    lfs_t lfs;
@@ -651,13 +713,17 @@ code = '''
    memcpy(&cfgp, cfg, sizeof(cfgp));
    lfsp_t lfsp;
    lfsp_mount(&lfsp, &cfgp) => 0;
+
    lfsp_unmount(&lfsp) => 0;
 '''

 # test we can read dirs in an old version
 [cases.test_compat_backward_read_dirs]
 defines.COUNT = 5
-if = 'LFS_VERSION == LFSP_VERSION'
+if = '''
+    LFS_DISK_VERSION == LFSP_DISK_VERSION
+        && DISK_VERSION == 0
+'''
 code = '''
    // create the new version
    lfs_t lfs;
@@ -709,7 +775,10 @@ code = '''
 defines.COUNT = 5
 defines.SIZE = [4, 32, 512, 8192]
 defines.CHUNK = 4
-if = 'LFS_VERSION == LFSP_VERSION'
+if = '''
+    LFS_DISK_VERSION == LFSP_DISK_VERSION
+        && DISK_VERSION == 0
+'''
 code = '''
    // create the new version
    lfs_t lfs;
@@ -791,7 +860,10 @@ code = '''
 defines.COUNT = 5
 defines.SIZE = [4, 32, 512, 8192]
 defines.CHUNK = 4
-if = 'LFS_VERSION == LFSP_VERSION'
+if = '''
+    LFS_DISK_VERSION == LFSP_DISK_VERSION
+        && DISK_VERSION == 0
+'''
 code = '''
    // create the new version
    lfs_t lfs;
@@ -898,7 +970,10 @@ code = '''
 # test we can write dirs in an old version
 [cases.test_compat_backward_write_dirs]
 defines.COUNT = 10
-if = 'LFS_VERSION == LFSP_VERSION'
+if = '''
+    LFS_DISK_VERSION == LFSP_DISK_VERSION
+        && DISK_VERSION == 0
+'''
 code = '''
    // create the new version
    lfs_t lfs;
@@ -957,7 +1032,10 @@ code = '''
 defines.COUNT = 5
 defines.SIZE = [4, 32, 512, 8192]
 defines.CHUNK = 2
-if = 'LFS_VERSION == LFSP_VERSION'
+if = '''
+    LFS_DISK_VERSION == LFSP_DISK_VERSION
+        && DISK_VERSION == 0
+'''
 code = '''
    // create the previous version
    lfs_t lfs;
@@ -1071,7 +1149,10 @@ code = '''
 defines.COUNT = 5
 defines.SIZE = [4, 32, 512, 8192]
 defines.CHUNK = 2
-if = 'LFS_VERSION == LFSP_VERSION'
+if = '''
+    LFS_DISK_VERSION == LFSP_DISK_VERSION
+        && DISK_VERSION == 0
+'''
 code = '''
    // create the previous version
    lfs_t lfs;
@@ -1280,7 +1361,10 @@ code = '''
 # test that we correctly bump the minor version
 [cases.test_compat_minor_bump]
 in = 'lfs.c'
-if = 'LFS_DISK_VERSION_MINOR > 0'
+if = '''
+    LFS_DISK_VERSION_MINOR > 0
+        && DISK_VERSION == 0
+'''
 code = '''
    // create a superblock
    lfs_t lfs;
@@ -1316,45 +1400,54 @@ code = '''

    // mount should still work
    lfs_mount(&lfs, cfg) => 0;
+
+    struct lfs_fsinfo fsinfo;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.disk_version == LFS_DISK_VERSION-1);
+
    lfs_file_open(&lfs, &file, "test", LFS_O_RDONLY) => 0;
    uint8_t buffer[8];
    lfs_file_read(&lfs, &file, buffer, 8) => 8;
    assert(memcmp(buffer, "testtest", 8) == 0);
    lfs_file_close(&lfs, &file) => 0;
+
+    // minor version should be unchanged
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.disk_version == LFS_DISK_VERSION-1);
+
    lfs_unmount(&lfs) => 0;

    // if we write, we need to bump the minor version
    lfs_mount(&lfs, cfg) => 0;
+
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.disk_version == LFS_DISK_VERSION-1);
+
    lfs_file_open(&lfs, &file, "test", LFS_O_WRONLY | LFS_O_TRUNC) => 0;
    lfs_file_write(&lfs, &file, "teeeeest", 8) => 8;
    lfs_file_close(&lfs, &file) => 0;

-    // minor version should have changed
-    lfs_dir_fetch(&lfs, &mdir, (lfs_block_t[2]){0, 1}) => 0;
-    lfs_dir_get(&lfs, &mdir, LFS_MKTAG(0x7ff, 0x3ff, 0),
-            LFS_MKTAG(LFS_TYPE_INLINESTRUCT, 0, sizeof(superblock)),
-            &superblock)
-            => LFS_MKTAG(LFS_TYPE_INLINESTRUCT, 0, sizeof(superblock));
-    lfs_superblock_fromle32(&superblock);
-    assert((superblock.version >> 16) & 0xffff == LFS_DISK_VERSION_MAJOR);
-    assert((superblock.version >>  0) & 0xffff == LFS_DISK_VERSION_MINOR);
+    // minor version should be changed
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.disk_version == LFS_DISK_VERSION);
+
    lfs_unmount(&lfs) => 0;

    // and of course mount should still work
    lfs_mount(&lfs, cfg) => 0;
+
+    // minor version should have changed
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.disk_version == LFS_DISK_VERSION);
+
    lfs_file_open(&lfs, &file, "test", LFS_O_RDONLY) => 0;
    lfs_file_read(&lfs, &file, buffer, 8) => 8;
    assert(memcmp(buffer, "teeeeest", 8) == 0);
    lfs_file_close(&lfs, &file) => 0;

-    // minor version should have changed
-    lfs_dir_fetch(&lfs, &mdir, (lfs_block_t[2]){0, 1}) => 0;
-    lfs_dir_get(&lfs, &mdir, LFS_MKTAG(0x7ff, 0x3ff, 0),
-            LFS_MKTAG(LFS_TYPE_INLINESTRUCT, 0, sizeof(superblock)),
-            &superblock)
-            => LFS_MKTAG(LFS_TYPE_INLINESTRUCT, 0, sizeof(superblock));
-    lfs_superblock_fromle32(&superblock);
-    assert((superblock.version >> 16) & 0xffff == LFS_DISK_VERSION_MAJOR);
-    assert((superblock.version >>  0) & 0xffff == LFS_DISK_VERSION_MINOR);
+    // yep, still changed
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.disk_version == LFS_DISK_VERSION);
+
    lfs_unmount(&lfs) => 0;
 '''
--- a/tests/test_dirs.toml
+++ b/tests/test_dirs.toml
@@ -181,6 +181,10 @@ code = '''
 defines.N = [5, 11]
 if = 'BLOCK_COUNT >= 4*N'
 reentrant = true
+defines.POWERLOSS_BEHAVIOR = [
+    'LFS_EMUBD_POWERLOSS_NOOP',
+    'LFS_EMUBD_POWERLOSS_OOO',
+]
 code = '''
    lfs_t lfs;
    int err = lfs_mount(&lfs, cfg);
@@ -439,6 +443,10 @@ code = '''
 defines.N = [5, 25]
 if = 'N < BLOCK_COUNT/2'
 reentrant = true
+defines.POWERLOSS_BEHAVIOR = [
+    'LFS_EMUBD_POWERLOSS_NOOP',
+    'LFS_EMUBD_POWERLOSS_OOO',
+]
 code = '''
    lfs_t lfs;
    int err = lfs_mount(&lfs, cfg);
@@ -747,6 +755,11 @@ code = '''
    lfs_file_open(&lfs, &file, "potato",
            LFS_O_WRONLY | LFS_O_CREAT) => LFS_ERR_ISDIR;

+    lfs_file_open(&lfs, &file, "tacoto", LFS_O_WRONLY | LFS_O_CREAT) => 0;
+    lfs_file_close(&lfs, &file) => 0;
+    lfs_rename(&lfs, "tacoto", "potato") => LFS_ERR_ISDIR;
+    lfs_rename(&lfs, "potato", "tacoto") => LFS_ERR_NOTDIR;
+
    lfs_mkdir(&lfs, "/") => LFS_ERR_EXIST;
    lfs_file_open(&lfs, &file, "/",
            LFS_O_WRONLY | LFS_O_CREAT | LFS_O_EXCL) => LFS_ERR_EXIST;
@@ -770,6 +783,10 @@ code = '''
    lfs_dir_read(&lfs, &dir, &info) => 1;
    assert(info.type == LFS_TYPE_DIR);
    assert(strcmp(info.name, "potato") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_REG);
+    assert(strcmp(info.name, "tacoto") == 0);
+    assert(info.size == 0);
    lfs_dir_read(&lfs, &dir, &info) => 0;
    lfs_dir_close(&lfs, &dir) => 0;

@@ -790,6 +807,10 @@ code = '''
    lfs_dir_read(&lfs, &dir, &info) => 1;
    assert(info.type == LFS_TYPE_DIR);
    assert(strcmp(info.name, "potato") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_REG);
+    assert(strcmp(info.name, "tacoto") == 0);
+    assert(info.size == 0);
    lfs_dir_read(&lfs, &dir, &info) => 0;
    lfs_dir_close(&lfs, &dir) => 0;
    lfs_unmount(&lfs) => 0;
--- a/tests/test_exhaustion.toml
+++ b/tests/test_exhaustion.toml
@@ -1,7 +1,7 @@
 # test running a filesystem to exhaustion
 [cases.test_exhaustion_normal]
 defines.ERASE_CYCLES = 10
-defines.BLOCK_COUNT = 256 # small bd so test runs faster
+defines.ERASE_COUNT = 256 # small bd so test runs faster
 defines.BLOCK_CYCLES = 'ERASE_CYCLES / 2'
 defines.BADBLOCK_BEHAVIOR = [
    'LFS_EMUBD_BADBLOCK_PROGERROR',
@@ -94,7 +94,7 @@ exhausted:
 # which also requires expanding superblocks
 [cases.test_exhaustion_superblocks]
 defines.ERASE_CYCLES = 10
-defines.BLOCK_COUNT = 256 # small bd so test runs faster
+defines.ERASE_COUNT = 256 # small bd so test runs faster
 defines.BLOCK_CYCLES = 'ERASE_CYCLES / 2'
 defines.BADBLOCK_BEHAVIOR = [
    'LFS_EMUBD_BADBLOCK_PROGERROR',
@@ -188,7 +188,7 @@ exhausted:
 # wear-level test running a filesystem to exhaustion
 [cases.test_exhuastion_wear_leveling]
 defines.ERASE_CYCLES = 20
-defines.BLOCK_COUNT = 256 # small bd so test runs faster
+defines.ERASE_COUNT = 256 # small bd so test runs faster
 defines.BLOCK_CYCLES = 'ERASE_CYCLES / 2'
 defines.FILES = 10
 code = '''
@@ -288,7 +288,7 @@ exhausted:
 # wear-level test + expanding superblock
 [cases.test_exhaustion_wear_leveling_superblocks]
 defines.ERASE_CYCLES = 20
-defines.BLOCK_COUNT = 256 # small bd so test runs faster
+defines.ERASE_COUNT = 256 # small bd so test runs faster
 defines.BLOCK_CYCLES = 'ERASE_CYCLES / 2'
 defines.FILES = 10
 code = '''
@@ -385,7 +385,7 @@ exhausted:
 # test that we wear blocks roughly evenly
 [cases.test_exhaustion_wear_distribution]
 defines.ERASE_CYCLES = 0xffffffff
-defines.BLOCK_COUNT = 256 # small bd so test runs faster
+defines.ERASE_COUNT = 256 # small bd so test runs faster
 defines.BLOCK_CYCLES = [5, 4, 3, 2, 1]
 defines.CYCLES = 100
 defines.FILES = 10
--- a/tests/test_files.toml
+++ b/tests/test_files.toml
@@ -1,5 +1,6 @@

 [cases.test_files_simple]
+defines.INLINE_MAX = [0, -1, 8]
 code = '''
    lfs_t lfs;
    lfs_format(&lfs, cfg) => 0;
@@ -25,6 +26,7 @@ code = '''
 [cases.test_files_large]
 defines.SIZE = [32, 8192, 262144, 0, 7, 8193]
 defines.CHUNKSIZE = [31, 16, 33, 1, 1023]
+defines.INLINE_MAX = [0, -1, 8]
 code = '''
    lfs_t lfs;
    lfs_format(&lfs, cfg) => 0;
@@ -67,6 +69,7 @@ code = '''
 defines.SIZE1 = [32, 8192, 131072, 0, 7, 8193]
 defines.SIZE2 = [32, 8192, 131072, 0, 7, 8193]
 defines.CHUNKSIZE = [31, 16, 1]
+defines.INLINE_MAX = [0, -1, 8]
 code = '''
    lfs_t lfs;
    lfs_format(&lfs, cfg) => 0;
@@ -152,6 +155,7 @@ code = '''
 defines.SIZE1 = [32, 8192, 131072, 0, 7, 8193]
 defines.SIZE2 = [32, 8192, 131072, 0, 7, 8193]
 defines.CHUNKSIZE = [31, 16, 1]
+defines.INLINE_MAX = [0, -1, 8]
 code = '''
    lfs_t lfs;
    lfs_format(&lfs, cfg) => 0;
@@ -232,6 +236,7 @@ code = '''
 defines.SIZE1 = [32, 8192, 131072, 0, 7, 8193]
 defines.SIZE2 = [32, 8192, 131072, 0, 7, 8193]
 defines.CHUNKSIZE = [31, 16, 1]
+defines.INLINE_MAX = [0, -1, 8]
 code = '''
    lfs_t lfs;
    lfs_format(&lfs, cfg) => 0;
@@ -303,7 +308,12 @@ code = '''
 [cases.test_files_reentrant_write]
 defines.SIZE = [32, 0, 7, 2049]
 defines.CHUNKSIZE = [31, 16, 65]
+defines.INLINE_MAX = [0, -1, 8]
 reentrant = true
+defines.POWERLOSS_BEHAVIOR = [
+    'LFS_EMUBD_POWERLOSS_NOOP',
+    'LFS_EMUBD_POWERLOSS_OOO',
+]
 code = '''
    lfs_t lfs;
    int err = lfs_mount(&lfs, cfg);
@@ -354,11 +364,20 @@ code = '''
 [cases.test_files_reentrant_write_sync]
 defines = [
    # append (O(n))
-    {MODE='LFS_O_APPEND',   SIZE=[32, 0, 7, 2049],  CHUNKSIZE=[31, 16, 65]},
+    {MODE='LFS_O_APPEND',
+        SIZE=[32, 0, 7, 2049],
+        CHUNKSIZE=[31, 16, 65],
+        INLINE_MAX=[0, -1, 8]},
    # truncate (O(n^2))
-    {MODE='LFS_O_TRUNC',    SIZE=[32, 0, 7, 200],   CHUNKSIZE=[31, 16, 65]},
+    {MODE='LFS_O_TRUNC',
+        SIZE=[32, 0, 7, 200],
+        CHUNKSIZE=[31, 16, 65],
+        INLINE_MAX=[0, -1, 8]},
    # rewrite (O(n^2))
-    {MODE=0,                SIZE=[32, 0, 7, 200],   CHUNKSIZE=[31, 16, 65]},
+    {MODE=0,
+        SIZE=[32, 0, 7, 200],
+        CHUNKSIZE=[31, 16, 65],
+        INLINE_MAX=[0, -1, 8]},
 ]
 reentrant = true
 code = '''
@@ -485,6 +504,10 @@ code = '''
 [cases.test_files_many_power_loss]
 defines.N = 300
 reentrant = true
+defines.POWERLOSS_BEHAVIOR = [
+    'LFS_EMUBD_POWERLOSS_NOOP',
+    'LFS_EMUBD_POWERLOSS_OOO',
+]
 code = '''
    lfs_t lfs;
    int err = lfs_mount(&lfs, cfg);
--- a/tests/test_interspersed.toml
+++ b/tests/test_interspersed.toml
@@ -195,6 +195,10 @@ code = '''
 defines.SIZE = [10, 100]
 defines.FILES = [4, 10, 26] 
 reentrant = true
+defines.POWERLOSS_BEHAVIOR = [
+    'LFS_EMUBD_POWERLOSS_NOOP',
+    'LFS_EMUBD_POWERLOSS_OOO',
+]
 code = '''
    lfs_t lfs;
    lfs_file_t files[FILES];
--- a/tests/test_move.toml
+++ b/tests/test_move.toml
@@ -357,6 +357,10 @@ code = '''

 [cases.test_move_reentrant_file]
 reentrant = true
+defines.POWERLOSS_BEHAVIOR = [
+    'LFS_EMUBD_POWERLOSS_NOOP',
+    'LFS_EMUBD_POWERLOSS_OOO',
+]
 code = '''
    lfs_t lfs;
    int err = lfs_mount(&lfs, cfg);
@@ -839,6 +843,10 @@ code = '''

 [cases.test_reentrant_dir]
 reentrant = true
+defines.POWERLOSS_BEHAVIOR = [
+    'LFS_EMUBD_POWERLOSS_NOOP',
+    'LFS_EMUBD_POWERLOSS_OOO',
+]
 code = '''
    lfs_t lfs;
    int err = lfs_mount(&lfs, cfg);
--- a/tests/test_orphans.toml
+++ b/tests/test_orphans.toml
@@ -98,7 +98,7 @@ code = '''
    lfs_mount(&lfs, cfg) => 0;
    // create an orphan
    lfs_mdir_t orphan;
-    lfs_alloc_ack(&lfs);
+    lfs_alloc_ckpoint(&lfs);
    lfs_dir_alloc(&lfs, &orphan) => 0;
    lfs_dir_commit(&lfs, &orphan, NULL, 0) => 0;

@@ -170,7 +170,7 @@ code = '''
    lfs_mount(&lfs, cfg) => 0;
    // create an orphan
    lfs_mdir_t orphan;
-    lfs_alloc_ack(&lfs);
+    lfs_alloc_ckpoint(&lfs);
    lfs_dir_alloc(&lfs, &orphan) => 0;
    lfs_dir_commit(&lfs, &orphan, NULL, 0) => 0;

--- a/tests/test_powerloss.toml
+++ b/tests/test_powerloss.toml
@@ -90,7 +90,10 @@ code = '''

 # partial prog, may not be byte in order!
 [cases.test_powerloss_partial_prog]
-if = "PROG_SIZE < BLOCK_SIZE"
+if = '''
+    PROG_SIZE < BLOCK_SIZE
+        && (DISK_VERSION == 0 || DISK_VERSION >= 0x00020001)
+'''
 defines.BYTE_OFF = ["0", "PROG_SIZE-1", "PROG_SIZE/2"]
 defines.BYTE_VALUE = [0x33, 0xcc]
 in = "lfs.c"
--- a/tests/test_seek.toml
+++ b/tests/test_seek.toml
@@ -329,6 +329,10 @@ code = '''
 # must be power-of-2 for quadratic probing to be exhaustive
 defines.COUNT = [4, 64, 128]
 reentrant = true
+defines.POWERLOSS_BEHAVIOR = [
+    'LFS_EMUBD_POWERLOSS_NOOP',
+    'LFS_EMUBD_POWERLOSS_OOO',
+]
 code = '''
    lfs_t lfs;
    int err = lfs_mount(&lfs, cfg);
--- a/tests/test_superblocks.toml
+++ b/tests/test_superblocks.toml
@@ -14,9 +14,28 @@ code = '''
    lfs_unmount(&lfs) => 0;
 '''

+# mount/unmount from interpretting a previous superblock block_count
+[cases.test_superblocks_mount_unknown_block_count]
+code = '''
+    lfs_t lfs;
+    lfs_format(&lfs, cfg) => 0;
+
+    memset(&lfs, 0, sizeof(lfs));
+    struct lfs_config tweaked_cfg = *cfg;
+    tweaked_cfg.block_count = 0;
+    lfs_mount(&lfs, &tweaked_cfg) => 0;
+    assert(lfs.block_count == cfg->block_count);
+    lfs_unmount(&lfs) => 0;
+'''
+
+
 # reentrant format
 [cases.test_superblocks_reentrant_format]
 reentrant = true
+defines.POWERLOSS_BEHAVIOR = [
+    'LFS_EMUBD_POWERLOSS_NOOP',
+    'LFS_EMUBD_POWERLOSS_OOO',
+]
 code = '''
    lfs_t lfs;
    int err = lfs_mount(&lfs, cfg);
@@ -34,6 +53,54 @@ code = '''
    lfs_mount(&lfs, cfg) => LFS_ERR_CORRUPT;
 '''

+# test we can read superblock info through lfs_fs_stat
+[cases.test_superblocks_stat]
+if = 'DISK_VERSION == 0'
+code = '''
+    lfs_t lfs;
+    lfs_format(&lfs, cfg) => 0;
+
+    // test we can mount and read fsinfo
+    lfs_mount(&lfs, cfg) => 0;
+
+    struct lfs_fsinfo fsinfo;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.disk_version == LFS_DISK_VERSION);
+    assert(fsinfo.name_max == LFS_NAME_MAX);
+    assert(fsinfo.file_max == LFS_FILE_MAX);
+    assert(fsinfo.attr_max == LFS_ATTR_MAX);
+
+    lfs_unmount(&lfs) => 0;
+'''
+
+[cases.test_superblocks_stat_tweaked]
+if = 'DISK_VERSION == 0'
+defines.TWEAKED_NAME_MAX = 63
+defines.TWEAKED_FILE_MAX = '(1 << 16)-1'
+defines.TWEAKED_ATTR_MAX = 512
+code = '''
+    // create filesystem with tweaked params
+    struct lfs_config tweaked_cfg = *cfg;
+    tweaked_cfg.name_max = TWEAKED_NAME_MAX;
+    tweaked_cfg.file_max = TWEAKED_FILE_MAX;
+    tweaked_cfg.attr_max = TWEAKED_ATTR_MAX;
+
+    lfs_t lfs;
+    lfs_format(&lfs, &tweaked_cfg) => 0;
+
+    // test we can mount and read these params with the original config
+    lfs_mount(&lfs, cfg) => 0;
+
+    struct lfs_fsinfo fsinfo;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.disk_version == LFS_DISK_VERSION);
+    assert(fsinfo.name_max == TWEAKED_NAME_MAX);
+    assert(fsinfo.file_max == TWEAKED_FILE_MAX);
+    assert(fsinfo.attr_max == TWEAKED_ATTR_MAX);
+
+    lfs_unmount(&lfs) => 0;
+'''
+
 # expanding superblock
 [cases.test_superblocks_expand]
 defines.BLOCK_CYCLES = [32, 33, 1]
@@ -111,6 +178,10 @@ code = '''
 defines.BLOCK_CYCLES = [2, 1]
 defines.N = 24
 reentrant = true
+defines.POWERLOSS_BEHAVIOR = [
+    'LFS_EMUBD_POWERLOSS_NOOP',
+    'LFS_EMUBD_POWERLOSS_OOO',
+]
 code = '''
    lfs_t lfs;
    int err = lfs_mount(&lfs, cfg);
@@ -149,3 +220,255 @@ code = '''
    assert(info.type == LFS_TYPE_REG);
    lfs_unmount(&lfs) => 0;
 '''
+
+# mount with unknown block_count
+[cases.test_superblocks_unknown_blocks]
+code = '''
+    lfs_t lfs;
+    lfs_format(&lfs, cfg) => 0;
+
+    // known block_size/block_count
+    cfg->block_size = BLOCK_SIZE;
+    cfg->block_count = BLOCK_COUNT;
+    lfs_mount(&lfs, cfg) => 0;
+    struct lfs_fsinfo fsinfo;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.block_size == BLOCK_SIZE);
+    assert(fsinfo.block_count == BLOCK_COUNT);
+    lfs_unmount(&lfs) => 0;
+
+    // unknown block_count
+    cfg->block_size = BLOCK_SIZE;
+    cfg->block_count = 0;
+    lfs_mount(&lfs, cfg) => 0;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.block_size == BLOCK_SIZE);
+    assert(fsinfo.block_count == BLOCK_COUNT);
+    lfs_unmount(&lfs) => 0;
+
+    // do some work
+    lfs_mount(&lfs, cfg) => 0;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.block_size == BLOCK_SIZE);
+    assert(fsinfo.block_count == BLOCK_COUNT);
+    lfs_file_t file;
+    lfs_file_open(&lfs, &file, "test",
+            LFS_O_CREAT | LFS_O_EXCL | LFS_O_WRONLY) => 0;
+    lfs_file_write(&lfs, &file, "hello!", 6) => 6;
+    lfs_file_close(&lfs, &file) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    lfs_mount(&lfs, cfg) => 0;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.block_size == BLOCK_SIZE);
+    assert(fsinfo.block_count == BLOCK_COUNT);
+    lfs_file_open(&lfs, &file, "test", LFS_O_RDONLY) => 0;
+    uint8_t buffer[256];
+    lfs_file_read(&lfs, &file, buffer, sizeof(buffer)) => 6;
+    lfs_file_close(&lfs, &file) => 0;
+    assert(memcmp(buffer, "hello!", 6) == 0);
+    lfs_unmount(&lfs) => 0;
+'''
+
+# mount with blocks fewer than the erase_count
+[cases.test_superblocks_fewer_blocks]
+defines.BLOCK_COUNT = ['ERASE_COUNT/2', 'ERASE_COUNT/4', '2']
+code = '''
+    lfs_t lfs;
+    lfs_format(&lfs, cfg) => 0;
+
+    // known block_size/block_count
+    cfg->block_size = BLOCK_SIZE;
+    cfg->block_count = BLOCK_COUNT;
+    lfs_mount(&lfs, cfg) => 0;
+    struct lfs_fsinfo fsinfo;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.block_size == BLOCK_SIZE);
+    assert(fsinfo.block_count == BLOCK_COUNT);
+    lfs_unmount(&lfs) => 0;
+
+    // incorrect block_count
+    cfg->block_size = BLOCK_SIZE;
+    cfg->block_count = ERASE_COUNT;
+    lfs_mount(&lfs, cfg) => LFS_ERR_INVAL;
+
+    // unknown block_count
+    cfg->block_size = BLOCK_SIZE;
+    cfg->block_count = 0;
+    lfs_mount(&lfs, cfg) => 0;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.block_size == BLOCK_SIZE);
+    assert(fsinfo.block_count == BLOCK_COUNT);
+    lfs_unmount(&lfs) => 0;
+
+    // do some work
+    lfs_mount(&lfs, cfg) => 0;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.block_size == BLOCK_SIZE);
+    assert(fsinfo.block_count == BLOCK_COUNT);
+    lfs_file_t file;
+    lfs_file_open(&lfs, &file, "test",
+            LFS_O_CREAT | LFS_O_EXCL | LFS_O_WRONLY) => 0;
+    lfs_file_write(&lfs, &file, "hello!", 6) => 6;
+    lfs_file_close(&lfs, &file) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    lfs_mount(&lfs, cfg) => 0;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.block_size == BLOCK_SIZE);
+    assert(fsinfo.block_count == BLOCK_COUNT);
+    lfs_file_open(&lfs, &file, "test", LFS_O_RDONLY) => 0;
+    uint8_t buffer[256];
+    lfs_file_read(&lfs, &file, buffer, sizeof(buffer)) => 6;
+    lfs_file_close(&lfs, &file) => 0;
+    assert(memcmp(buffer, "hello!", 6) == 0);
+    lfs_unmount(&lfs) => 0;
+'''
+
+# mount with more blocks than the erase_count
+[cases.test_superblocks_more_blocks]
+defines.FORMAT_BLOCK_COUNT = '2*ERASE_COUNT'
+in = 'lfs.c'
+code = '''
+    lfs_t lfs;
+    lfs_init(&lfs, cfg) => 0;
+    lfs.block_count = BLOCK_COUNT;
+
+    lfs_mdir_t root = {
+        .pair = {0, 0}, // make sure this goes into block 0
+        .rev = 0,
+        .off = sizeof(uint32_t),
+        .etag = 0xffffffff,
+        .count = 0,
+        .tail = {LFS_BLOCK_NULL, LFS_BLOCK_NULL},
+        .erased = false,
+        .split = false,
+    };
+
+    lfs_superblock_t superblock = {
+        .version     = LFS_DISK_VERSION,
+        .block_size  = BLOCK_SIZE,
+        .block_count = FORMAT_BLOCK_COUNT,
+        .name_max    = LFS_NAME_MAX,
+        .file_max    = LFS_FILE_MAX,
+        .attr_max    = LFS_ATTR_MAX,
+    };
+
+    lfs_superblock_tole32(&superblock);
+    lfs_dir_commit(&lfs, &root, LFS_MKATTRS(
+            {LFS_MKTAG(LFS_TYPE_CREATE, 0, 0), NULL},
+            {LFS_MKTAG(LFS_TYPE_SUPERBLOCK, 0, 8), "littlefs"},
+            {LFS_MKTAG(LFS_TYPE_INLINESTRUCT, 0, sizeof(superblock)),
+                &superblock})) => 0;
+    lfs_deinit(&lfs) => 0;
+
+    // known block_size/block_count
+    cfg->block_size = BLOCK_SIZE;
+    cfg->block_count = BLOCK_COUNT;
+    lfs_mount(&lfs, cfg) => LFS_ERR_INVAL;
+'''
+
+# mount and grow the filesystem
+[cases.test_superblocks_grow]
+defines.BLOCK_COUNT = ['ERASE_COUNT/2', 'ERASE_COUNT/4', '2']
+defines.BLOCK_COUNT_2 = 'ERASE_COUNT'
+defines.KNOWN_BLOCK_COUNT = [true, false]
+code = '''
+    lfs_t lfs;
+    lfs_format(&lfs, cfg) => 0;
+
+    if (KNOWN_BLOCK_COUNT) {
+        cfg->block_count = BLOCK_COUNT;
+    } else {
+        cfg->block_count = 0;
+    }
+
+    // mount with block_size < erase_size
+    lfs_mount(&lfs, cfg) => 0;
+    struct lfs_fsinfo fsinfo;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.block_size == BLOCK_SIZE);
+    assert(fsinfo.block_count == BLOCK_COUNT);
+    lfs_unmount(&lfs) => 0;
+
+    // same size is a noop
+    lfs_mount(&lfs, cfg) => 0;
+    lfs_fs_grow(&lfs, BLOCK_COUNT) => 0;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.block_size == BLOCK_SIZE);
+    assert(fsinfo.block_count == BLOCK_COUNT);
+    lfs_unmount(&lfs) => 0;
+
+    lfs_mount(&lfs, cfg) => 0;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.block_size == BLOCK_SIZE);
+    assert(fsinfo.block_count == BLOCK_COUNT);
+    lfs_unmount(&lfs) => 0;
+
+    // grow to new size
+    lfs_mount(&lfs, cfg) => 0;
+    lfs_fs_grow(&lfs, BLOCK_COUNT_2) => 0;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.block_size == BLOCK_SIZE);
+    assert(fsinfo.block_count == BLOCK_COUNT_2);
+    lfs_unmount(&lfs) => 0;
+
+    if (KNOWN_BLOCK_COUNT) {
+        cfg->block_count = BLOCK_COUNT_2;
+    } else {
+        cfg->block_count = 0;
+    }
+
+    lfs_mount(&lfs, cfg) => 0;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.block_size == BLOCK_SIZE);
+    assert(fsinfo.block_count == BLOCK_COUNT_2);
+    lfs_unmount(&lfs) => 0;
+
+    // mounting with the previous size should fail
+    cfg->block_count = BLOCK_COUNT;
+    lfs_mount(&lfs, cfg) => LFS_ERR_INVAL;
+
+    if (KNOWN_BLOCK_COUNT) {
+        cfg->block_count = BLOCK_COUNT_2;
+    } else {
+        cfg->block_count = 0;
+    }
+
+    // same size is a noop
+    lfs_mount(&lfs, cfg) => 0;
+    lfs_fs_grow(&lfs, BLOCK_COUNT_2) => 0;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.block_size == BLOCK_SIZE);
+    assert(fsinfo.block_count == BLOCK_COUNT_2);
+    lfs_unmount(&lfs) => 0;
+
+    lfs_mount(&lfs, cfg) => 0;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.block_size == BLOCK_SIZE);
+    assert(fsinfo.block_count == BLOCK_COUNT_2);
+    lfs_unmount(&lfs) => 0;
+
+    // do some work
+    lfs_mount(&lfs, cfg) => 0;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.block_size == BLOCK_SIZE);
+    assert(fsinfo.block_count == BLOCK_COUNT_2);
+    lfs_file_t file;
+    lfs_file_open(&lfs, &file, "test",
+            LFS_O_CREAT | LFS_O_EXCL | LFS_O_WRONLY) => 0;
+    lfs_file_write(&lfs, &file, "hello!", 6) => 6;
+    lfs_file_close(&lfs, &file) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    lfs_mount(&lfs, cfg) => 0;
+    lfs_fs_stat(&lfs, &fsinfo) => 0;
+    assert(fsinfo.block_size == BLOCK_SIZE);
+    assert(fsinfo.block_count == BLOCK_COUNT_2);
+    lfs_file_open(&lfs, &file, "test", LFS_O_RDONLY) => 0;
+    uint8_t buffer[256];
+    lfs_file_read(&lfs, &file, buffer, sizeof(buffer)) => 6;
+    lfs_file_close(&lfs, &file) => 0;
+    assert(memcmp(buffer, "hello!", 6) == 0);
+    lfs_unmount(&lfs) => 0;
+'''
--- a/tests/test_truncate.toml
+++ b/tests/test_truncate.toml
@@ -231,6 +231,10 @@ defines.SMALLSIZE = [4, 512]
 defines.MEDIUMSIZE = [0, 3, 4, 5, 31, 32, 33, 511, 512, 513, 1023, 1024, 1025]
 defines.LARGESIZE = 2048
 reentrant = true
+defines.POWERLOSS_BEHAVIOR = [
+    'LFS_EMUBD_POWERLOSS_NOOP',
+    'LFS_EMUBD_POWERLOSS_OOO',
+]
 code = '''
    lfs_t lfs;
    int err = lfs_mount(&lfs, cfg);