mcp_fs

A simple, slow, ultracompact filesystem.

#define MY_BLOCK_SIZE 2048
#define MY_BLOCK_COUNT 16
static int read_block(void * cb_ctx, int block_index, void * dst) {
    my_read_block(dst, block_index);
    return 0;
}
static int write_block(void * cb_ctx, int block_index, const void * src) {
    my_write_block(src, block_index);
    return 0;
}
static uint8_t aligned_aux_memory[MFS_ALIGNED_AUX_MEMORY_SIZE(BLOCK_SIZE, BLOCK_COUNT)] __attribute__((aligned));
static const mfs_conf_t conf = {
    aligned_aux_memory,
    BLOCK_SIZE,
    BLOCK_COUNT,
    cb_ctx,
    read_block,
    write_block
};
static mfs_t mfs;
int err = mfs_mount(&mfs, &conf);
assert(err == 0);
err = mfs_open(&mfs, "foo.txt", MFS_MODE_WRITE);
assert(err == 0);
/* ... */

Properties:

• No directories
• Only one open file at a time.
• Mounting an existing volume requires that all the blocks are scanned. Only practical for small volumes.
• 1 file == 1 or more blocks. No metadata blocks.
• A file can be stored across blocks that are not contiguous. This is fairly standard.
• Re-writing an existing file is power-failure tollerant. The changes are committed atomically. The original file contents will always be seen after a power interruption. Only a successful file close commits the new file contents.