Re: [PATCH v2 0/3] btrfs-progs: image: make restored image file to be properly enlarged

[David Sterba <dsterba@suse.cz>]

On Thu, Apr 29, 2021 at 05:06:55PM +0800, Qu Wenruo wrote:
> Recent kernel will refuse to mount restored image, even the source fs is
> empty:
>  # mkfs.btrfs -f /dev/test/test
>  # btrfs-image /dev/test/test /tmp/dump
>  # btrfs-image -r /tmp/dump ~/test.img
>  # mount ~/test.img /mnt/btrfs
>  mount: /mnt/btrfs: wrong fs type, bad option, bad superblock on /dev/loop0, missing codepage or helper program, or other error.
>  # dmesg -t | tail -n 7
>  loop0: detected capacity change from 10592 to 0
>  BTRFS info (device loop0): disk space caching is enabled
>  BTRFS info (device loop0): has skinny extents
>  BTRFS info (device loop0): flagging fs with big metadata feature
>  BTRFS error (device loop0): device total_bytes should be at most 5423104 but found 10737418240
>  BTRFS error (device loop0): failed to read chunk tree: -22
>  BTRFS error (device loop0): open_ctree failed
> 
> This is triggered by a recent kernel commit 3a160a933111 ("btrfs: drop never met disk total
> bytes check in verify_one_dev_extent").
> 
> But the root cause is, we didn't enlarge the output file if the source
> image only contains single device.
> 
> This bug won't affect restore to block device, or the destination file
> is already large enough.
> 
> This patchset will fix the problem, and with new test case to detect
> such problem.
> 
> Also remove one dead code exposed during the development.
> 
> Changelog:
> v2:
> - Comments word change
> - Only enlarge the file when the target file is smaller than expected
>   device size
> - Change the prefix of the 1st patch
>   From "btrfs" to "btrfs-progs"
> 
> Qu Wenruo (3):
>   btrfs-progs: image: remove the dead stat() call
>   btrfs-progs: image: enlarge the output file if no tree modification is
>     needed for restore
>   btrfs-progs: misc-tests: add test to ensure the restored image can be
>     mounted

Added to devel, thanks.