CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK was undocumented and not error checked

closes #2431.

cpukit/sapi/include/confdefs.h

@@ -3820,5 +3820,19 @@ const rtems_libio_helper rtems_fs_init_helper =
   #endif
 #endif
 
+/*
+ * IMFS block size for in memory files (memfiles) must be a power of
+ * two between 16 and 512 inclusive.
+ */
+#if ((CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK != 16) && \
+     (CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK != 32) && \
+     (CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK != 64) && \
+     (CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK != 128) && \
+     (CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK != 256) && \
+     (CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK != 512))
+  #error "IMFS Memfile block size must be a power of 2 between 16 and 512"
+#endif
+
+
 #endif
 /* end of include file */

doc/user/conf.t

@@ -2748,6 +2748,61 @@ options will be defined as well
 @item @code{CONFIGURE_IMFS_DISABLE_UNMOUNT}.
 @end itemize
 
+@c
+@c === CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK ===
+@c
+@subsection Specify Block Size for IMFS
+
+@findex CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK
+
+@table @b
+@item CONSTANT:
+@code{CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK}
+
+@item DATA TYPE:
+Boolean feature macro.
+
+@item RANGE:
+Valid values for this configuration parameter are a power of two (2)
+between 16 and 512 inclusive.  In other words, valid values are 16,
+32, 64, 128, 256,and 512.
+
+@item DEFAULT VALUE:
+The default IMFS block size is 128 bytes.
+
+@end table
+
+@subheading DESCRIPTION:
+This configuration parameter specifies the block size for in-memory files
+managed by the IMFS. The configured block size has two impacts. The first
+is the average amount of unused memory in the last block of each file. For
+example, when the block size is 512, on average one-half of the last block
+of each file will remain unused and the memory is wasted. In contrast,
+when the block size is 16, the average unused memory per file is only
+8 bytes. However, it requires more allocations for the same size file
+and thus more overhead per block for the dynamic memory management.
+
+Second, the block size has an impact on the maximum size file that can
+be stored in the IMFS. With smaller block size, the maximum file size
+is correspondingly smaller. The following shows the maximum file size
+possible based on the configured block size:
+
+@itemize @bullet
+@item when the block size is 16 bytes, the maximum file size is 1,328
+bytes.
+@item when the block size is 32 bytes, the maximum file size is 18,656
+bytes.
+@item when the block size is 64 bytes, the maximum file size is 279,488
+bytes.
+@item when the block size is 128 bytes, the maximum file size is
+4,329,344 bytes.
+@item when the block size is 256 bytes, the maximum file size is
+68,173,568 bytes.
+@item when the block size is 512 bytes, the maximum file size is
+1,082,195,456 bytes.
+@end itemize
+
+
 @c
 @c === CONFIGURE_IMFS_DISABLE_CHOWN ===
 @c

testsuites/psxtests/psximfs02/init.c

@@ -1,5 +1,5 @@
 /*
- *  COPYRIGHT (c) 1989-2014.
+ *  COPYRIGHT (c) 1989-2015.
  *  On-Line Applications Research Corporation (OAR).
  *
  *  The license and distribution terms for this file may be
@@ -211,7 +211,7 @@ rtems_task Init(
 #define CONFIGURE_FILESYSTEM_IMFS
 
 #define CONFIGURE_MAXIMUM_TASKS                  1
-#define CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK   15
+#define CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK   16
 #define CONFIGURE_LIBIO_MAXIMUM_FILE_DESCRIPTORS 4
 #define CONFIGURE_INITIAL_EXTENSIONS RTEMS_TEST_INITIAL_EXTENSION