On Wed, 29 Aug 2007 17:27:07 +0800 常青 wrote:
[adding maintainer cc:]
> I've been encountered with a FAT panic, saying,
> =====================================
> Filesystem panic (dev mmcblk0p1)
> fat_get_cluster: invalid cluster chain (i_pos 16021)
> File system has been set read-only
> =====================================
>
> After tracking into kernel code, I find this is printed out by
> fat_get_cluster@fs/fat/cache.c ,
> =====================================
> nr = fat_access(sb, *dclus, -1);
> if (nr < 0)
> return nr;
> else if (nr == FAT_ENT_FREE) {
> fat_fs_panic(sb, "%s: invalid cluster chain"
> " (i_pos %lld)", __FUNCTION__,
> MSDOS_I(inode)->i_pos);
> return -EIO;
> } else if (nr == FAT_ENT_EOF) {
> fat_cache_add(inode, &cid);
> return FAT_ENT_EOF;
> }
> =====================================
>
> Could you please help to explain what does FAT_ENT_FREE mean? and what
> condition will lead to (nr == FAT_ENT_FREE) to be true?
#define FAT_ENT_FREE (0)
It means that the FAT filesystem cluster chain came upon an entry
with a value of 0, which is invalid. I.e., it means that this
cluster (of blocks) is free, not part of a file, but the code was
trying to follow a chain of clusters for a file, in which case it
should never see a 0, just valid cluster links until EOF (value)
is reached.
Sounds like the FAT is corrupted.
Hirofumi, is there second copy of the FAT table? If so, is there
a way to use it? or just dd copy#2 to copy#1?
> Thank you very much!
>
> Sorry for these simple questions for you, since it's the first time
> for me to look into FAT code. Your kindly reply will be appreciated
> much, and will help me a lot.
>
> BTW, where could I find a documentation about Linux FAT?
There's not much that I can find. Documentation/filesystems/vfat.txt
is outdated (doesn't even list the current maintainer).
vfat.txt mentions http://bmrc.berkeley.edu/people/chaffee/fat32.html,
which has a little documentation, but don't bother with the patches
there -- they are all very old.
> Thanks & Regards,
> Stephen
HTH.
---
~Randy
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