SROFS is a simple design of a readonly filesystem for embedded systems such as Atmel ATmega based microcontroller boards (Arduino in mind).
Features (as of version 0 of the filesystem):
- max. number of files: 65536
- max. block size: 64K
- max. file path (not name) length: 117 chars + '\0' terminator
A SROFS filesystem consists of
- a superblock (starting at device/partition block 0)
- a file index
- one or more files
There are no directories although the filesystem API may provide virtual access to directory structures.
[0-4] MAGIC "SROFS" filesystem identifier
[5 ] VERSION SROFS version number, currently 0
[6 ] BLOCKSIZE Size of a logical filesystem block, 2^BLOCKSIZE
default 9 = 2^9 = 512 byte blocks
[7 ] INDEX_START Logical blocknumber of first file index block
[8-9] NUM_FILES Number of files in this filesystem.
[File Entry]* NUM_FILES times the file entry structure; the file
entries are orded alphabetically (see later).
[0-117] FILE_PATH NUL terminated string containing the complete file
path (ASCII), e.g. "wwwroot/foo/bar.txt"
[118-121] NUM_BLOCKS Number of used logical blocks
[122-125] FIRST_BLOCK Logical block index of first data block
[126-127] LAST_BLOCK_SIZE Number of octets used in last data block
File lookup can be done using the following (pseudo) code for a binary search:
min = 0
max = NUM_FILES - 1
WHILE min <= max
m = (min + max) / 2
IF file < entry[m]
max = m - 1
ELSE IF file > entry[m]
min = m + 1
ELSE
RETURN entry[m]
END WHILE
RETURN File not found