imfs/user_allocator: Add user-configurable allocator support

- Extend IMFS and libio headers to define default allocator/deallocator ops
  and logic for configuring memfile_ops.
- Update imfs_memfile to use custom allocators for memory blocks.
- Fix imfs_statvfs.f_bfree calculation to respect user-defined ops.
- Add psximfs03 test case to validate custom allocator behavior.
- Refactor psximfs01 to share helper functions with psximfs03.

cpukit/include/rtems/confdefs/libio.h

@@ -200,6 +200,15 @@ extern "C" {
 
 const int imfs_memfile_bytes_per_block = CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK;
 
+/*
+ * Using the default ops if user doesn't configure ops
+ */
+#ifndef CONFIGURE_IMFS_MEMFILE_OPS
+  #define CONFIGURE_IMFS_MEMFILE_OPS IMFS_MEMFILE_DEFAULT_OPS
+#endif
+
+IMFS_memfile_ops_t imfs_memfile_ops = CONFIGURE_IMFS_MEMFILE_OPS;
+
 static IMFS_fs_info_t IMFS_root_fs_info;
 
 static const rtems_filesystem_operations_table IMFS_root_ops = {

cpukit/include/rtems/imfs.h

@@ -61,6 +61,9 @@ extern "C" {
 struct IMFS_jnode_tt;
 typedef struct IMFS_jnode_tt IMFS_jnode_t;
 
+typedef struct IMFS_memfile_ops_t IMFS_memfile_ops_t;
+extern IMFS_memfile_ops_t imfs_memfile_ops;
+
 /**
  *  IMFS "memfile" information
  *
@@ -283,6 +286,65 @@ struct IMFS_jnode_tt {
   const IMFS_node_control *control;
 };
 
+/**
+ * @brief The type of allocator function pointer.
+ */
+typedef void *(*IMFS_memfile_allocator)(void);
+
+/**
+ * @brief The type of deallocator function pointer.
+ */
+typedef void (*IMFS_memfile_deallocator)(
+  void *memory
+);
+
+/**
+ * @brief The get_free_space function pointer.
+ */
+typedef size_t (*IMFS_memfile_free_space)(void);
+
+/**
+ * @brief The ops table for user defined allocator-deallocator for
+ * IMFS memfile data blocks.
+ *
+ * @param allocate The function which will be used to allocate IMFS blocks.
+ * @param deallocate The function to deallocate the allocated data blocks.
+ * @param get_free_space The function used by kernel to get the free space.
+ */
+struct IMFS_memfile_ops_t {
+  IMFS_memfile_allocator allocate_block;
+  IMFS_memfile_deallocator free_block;
+  IMFS_memfile_free_space get_free_space;
+};
+
+/**
+ * @brief The default imfs block allocator
+ *
+ * @details The allocator uses the memory from the heap.
+ */
+void *IMFS_default_allocate_block(void);
+
+/**
+ * @brief The default imfs block deallocator
+ *
+ * @details The deallocator frees the memory which was taken from heap.
+ */
+void IMFS_default_deallocate_block(void *);
+
+/**
+ * @brief The default free space calculator
+ *
+ * @details The free_space function calculates the free space in heap.
+ */
+size_t IMFS_default_free_space(void);
+
+#define IMFS_MEMFILE_DEFAULT_OPS \
+{ \
+  .allocate_block = IMFS_default_allocate_block, \
+  .free_block = IMFS_default_deallocate_block, \
+  .get_free_space = IMFS_default_free_space \
+}
+
 typedef struct {
   IMFS_jnode_t                          Node;
   rtems_chain_control                   Entries;

cpukit/libfs/src/imfs/imfs_initsupp.c

@@ -40,6 +40,7 @@
 
 #include <rtems/imfs.h>
 
+#include <stdlib.h>
 #include <errno.h>
 
 int IMFS_initialize_support(
@@ -52,6 +53,10 @@ int IMFS_initialize_support(
   const IMFS_node_control *node_control;
   IMFS_jnode_t            *root_node;
 
+  _Assert(imfs_memfile_ops.allocate_block != NULL);
+  _Assert(imfs_memfile_ops.free_block != NULL);
+  _Assert(imfs_memfile_ops.get_free_space != NULL);
+
   mount_data = data;
 
   fs_info = mount_data->fs_info;

cpukit/libfs/src/imfs/imfs_memfile.c

@@ -38,6 +38,7 @@
 #include "config.h"
 #endif
 
+#include <rtems/libcsupport.h>
 #include <rtems/imfsimpl.h>
 
 #include <stdlib.h>
@@ -831,7 +832,7 @@ void *memfile_alloc_block(void)
 {
   void *memory;
 
-  memory = (void *)calloc(1, IMFS_MEMFILE_BYTES_PER_BLOCK);
+  memory = imfs_memfile_ops.allocate_block();
   if ( memory )
     memfile_blocks_allocated++;
 
@@ -847,10 +848,25 @@ void memfile_free_block(
   void *memory
 )
 {
-  free(memory);
+  imfs_memfile_ops.free_block(memory);
   memfile_blocks_allocated--;
 }
 
+void *IMFS_default_allocate_block(void)
+{
+  return (void *)calloc(1, IMFS_MEMFILE_BYTES_PER_BLOCK);
+}
+
+void IMFS_default_deallocate_block(void *memory)
+{
+  free(memory);
+}
+
+size_t IMFS_default_free_space(void)
+{
+  return malloc_free_space();
+}
+
 static const rtems_filesystem_file_handlers_r IMFS_memfile_handlers = {
   .open_h = rtems_filesystem_default_open,
   .close_h = rtems_filesystem_default_close,

cpukit/libfs/src/imfs/imfs_statvfs.c

@@ -47,8 +47,8 @@ int IMFS_statvfs(
   buf->f_bsize = IMFS_MEMFILE_BYTES_PER_BLOCK;
   buf->f_frsize = IMFS_MEMFILE_BYTES_PER_BLOCK;
   buf->f_blocks = UINT_MAX / IMFS_MEMFILE_BYTES_PER_BLOCK;
-  buf->f_bfree = malloc_free_space() / IMFS_MEMFILE_BYTES_PER_BLOCK;
-  buf->f_bavail = malloc_free_space() / IMFS_MEMFILE_BYTES_PER_BLOCK;
+  buf->f_bfree = imfs_memfile_ops.get_free_space() / IMFS_MEMFILE_BYTES_PER_BLOCK;
+  buf->f_bavail = imfs_memfile_ops.get_free_space() / IMFS_MEMFILE_BYTES_PER_BLOCK;
   buf->f_files = fs_info->jnode_count;
   buf->f_fsid = 1;
   buf->f_flag = loc->mt_entry->writeable;