| Submitter | Theodore Ts'o |
|---|---|
| Date | Feb. 17, 2012, 4:20 a.m. |
| Message ID | <20120217042038.GA9319@thunk.org> |
| Download | mbox | patch |
| Permalink | /patch/141730/ |
| State | Accepted |
| Headers | show |
Comments
Hi Ted, > mke2fs: allow file systems w/ uninit_bg to be recovered with mke2fs -S > > The command mke2fs -S is used as a last ditch recovery command to > write new superblock and block group descriptors, but _not_ to destroy > the inode table in hopes of recovering from a badly corrupted file > system. If the uninit_bg feature is enabled, we need to make sure to > clear the unused inodes count field in the block group descriptors or > else e2fsck -fy will leave the file system completely empty. > > Thanks to Akira Fujita for reporting this problem. I tried to mkfs -S and e2fsck to salvage file with e2fsprogs 1.42.1 (commit: 5ab348723247). But it seemed that the file was removed after e2fsck. Could you check my method (below script)? Am I missing something? --- #!/bin/bash DEV="" #device MP="" #mount point mke2fs -t ext4 $DEV mount -t ext4 $DEV $MP dd if=/dev/urandom of=$MP/FILE bs=4K count=100 #create file on ext4 ls -l $MP umount $DEV dd if=/dev/zero of=$DEV bs=4K count=1 #clear primary SB mke2fs -t ext4 -S -b 4096 $DEV #write out SB mount -t ext4 $DEV $MP #can't mount because of the gdp checksum difference e2fsck $DEV #can salvage? mount -t ext4 $DEV $MP ls -l $MP # It seems that "FILE" is removed umount $DEV --- Regards, Akira Fujita (2012/02/17 13:20), Ted Ts'o wrote: > On Thu, Dec 22, 2011 at 05:30:22PM +0900, Akira Fujita wrote: >> If we run the mke2fs with the -S option and the uninit_bg feature >> simultaneously, the mke2fs marks blockgroups as uninitialized. >> The e2fsck which run immediately after the mke2fs >> removes all of the files. >> >> To avoid this, the patch prohibits user from >> setting the -S option and the uninit_bg feature simultaneously. > > This is not the best fix. The best fix is to clear the itable_unused > fields in the block group descriptors if mke2fs -S is set. See below > for what I have in my tree. > > - Ted > > commit 9b6a158524fe82202bef6d0d8a101b47e6c02b64 > Author: Theodore Ts'o<tytso@mit.edu> > Date: Thu Feb 16 23:16:34 2012 -0500 > > mke2fs: allow file systems w/ uninit_bg to be recovered with mke2fs -S > > The command mke2fs -S is used as a last ditch recovery command to > write new superblock and block group descriptors, but _not_ to destroy > the inode table in hopes of recovering from a badly corrupted file > system. If the uninit_bg feature is enabled, we need to make sure to > clear the unused inodes count field in the block group descriptors or > else e2fsck -fy will leave the file system completely empty. > > Thanks to Akira Fujita for reporting this problem. > > Signed-off-by: "Theodore Ts'o"<tytso@mit.edu> > > diff --git a/misc/mke2fs.c b/misc/mke2fs.c > index 08789c4..c70c1b4 100644 > --- a/misc/mke2fs.c > +++ b/misc/mke2fs.c > @@ -2434,6 +2434,17 @@ int main (int argc, char *argv[]) > if (super_only) { > fs->super->s_state |= EXT2_ERROR_FS; > fs->flags&= ~(EXT2_FLAG_IB_DIRTY|EXT2_FLAG_BB_DIRTY); > + /* > + * The command "mke2fs -S" is used to recover > + * corrupted file systems, so do not mark any of the > + * inodes as unused; we want e2fsck to consider all > + * inodes as potentially containing recoverable data. > + */ > + if (fs->super->s_feature_ro_compat& > + EXT4_FEATURE_RO_COMPAT_GDT_CSUM) { > + for (i = 1; i< fs->group_desc_count; i++) > + ext2fs_bg_itable_unused_set(fs, i, 0); > + } > } else { > /* rsv must be a power of two (64kB is MD RAID sb alignment) */ > blk64_t rsv = 65536 / fs->blocksize; > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Patch
diff --git a/misc/mke2fs.c b/misc/mke2fs.c index 08789c4..c70c1b4 100644 --- a/misc/mke2fs.c +++ b/misc/mke2fs.c @@ -2434,6 +2434,17 @@ int main (int argc, char *argv[]) if (super_only) { fs->super->s_state |= EXT2_ERROR_FS; fs->flags &= ~(EXT2_FLAG_IB_DIRTY|EXT2_FLAG_BB_DIRTY); + /* + * The command "mke2fs -S" is used to recover + * corrupted file systems, so do not mark any of the + * inodes as unused; we want e2fsck to consider all + * inodes as potentially containing recoverable data. + */ + if (fs->super->s_feature_ro_compat & + EXT4_FEATURE_RO_COMPAT_GDT_CSUM) { + for (i = 1; i < fs->group_desc_count; i++) + ext2fs_bg_itable_unused_set(fs, i, 0); + } } else { /* rsv must be a power of two (64kB is MD RAID sb alignment) */ blk64_t rsv = 65536 / fs->blocksize;