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@xxxxxxx>
> 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@xxxxxxx>
>
> 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;
> --
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