Re: [9fans] ext2srv ?

[Alexander Viro <viro@math.psu.edu>]

On Tue, 14 Aug 2001, Russ Cox wrote:

> ext2srv is in /sys/lib/pcdist/cmd.  i'm not convinced
> of its reliability enough to run it in read-write
> mode, but that's just because it's been so long since
> i ran it.  for the distribution, i had to update one
> piece of on-disk data structure, and that scared me.
> specifically, the file name length has apparently
> always been a byte followed by an unused (zero) byte.
> ext2srv was reading the length as a short.  apparently
> the unused byte is now used, but i and ext2srv don't
> know what for.

It's a cached file type (for getdents(2)).

enum {
	S_SHIFT = 12	/* mode bits */
};
static unsigned char ext2_type_by_mode[S_IFMT >> S_SHIFT] = {
        [S_IFREG >> S_SHIFT]    EXT2_FT_REG_FILE,
        [S_IFDIR >> S_SHIFT]    EXT2_FT_DIR,
        [S_IFCHR >> S_SHIFT]    EXT2_FT_CHRDEV,
        [S_IFBLK >> S_SHIFT]    EXT2_FT_BLKDEV,
        [S_IFIFO >> S_SHIFT]    EXT2_FT_FIFO,
        [S_IFSOCK >> S_SHIFT]   EXT2_FT_SOCK,
        [S_IFLNK >> S_SHIFT]    EXT2_FT_SYMLINK,
};

and that byte will be ext2_type_by_mode[(inode->i_mode & S_IFMT) >> S_SHIFT]

ext2 superblock has a 32-bit bitmap (->s_feature_incompat). If ->s_rev_level
is 0 or bit 1 in ->s_feature_incompat (little-endian) is not set - leave
that byte zero. Otherwise set it as above.

BTW, you might want to check ext2 in recent tree - it got more readable
than it used to be.