Re: [PATCH] btrfs: send, fix wrong file path when there is an inode with a pending rmdir

[David Sterba <dsterba@suse.cz>]

On Thu, Dec 10, 2020 at 12:09:02PM +0000, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> When doing an incremental send, if we have a new inode that happens to
> have the same number that an old directory inode had in the base snapshot
> and that old directory has a pending rmdir operation, we end up computing
> a wrong path for the new inode, causing the receiver to fail.
> 
> Example reproducer:
> 
>   $ cat test-send-rmdir.sh
>   #!/bin/bash
> 
>   DEV=/dev/sdi
>   MNT=/mnt/sdi
> 
>   mkfs.btrfs -f $DEV >/dev/null
>   mount $DEV $MNT
> 
>   mkdir $MNT/dir
>   touch $MNT/dir/file1
>   touch $MNT/dir/file2
>   touch $MNT/dir/file3
> 
>   # Filesystem looks like:
>   #
>   # .                                     (ino 256)
>   # |----- dir/                           (ino 257)
>   #         |----- file1                  (ino 258)
>   #         |----- file2                  (ino 259)
>   #         |----- file3                  (ino 260)
>   #
> 
>   btrfs subvolume snapshot -r $MNT $MNT/snap1
>   btrfs send -f /tmp/snap1.send $MNT/snap1
> 
>   # Now remove our directory and all its files.
>   rm -fr $MNT/dir
> 
>   # Unmount the filesystem and mount it again. This is to ensure that
>   # the next inode that is created ends up with the same inode number
>   # that our directory "dir" had, 257, which is the first free "objectid"
>   # available after mounting again the filesystem.
>   umount $MNT
>   mount $DEV $MNT
> 
>   # Now create a new file (it could be a directory as well).
>   touch $MNT/newfile
> 
>   # Filesystem now looks like:
>   #
>   # .                                     (ino 256)
>   # |----- newfile                        (ino 257)
>   #
> 
>   btrfs subvolume snapshot -r $MNT $MNT/snap2
>   btrfs send -f /tmp/snap2.send -p $MNT/snap1 $MNT/snap2
> 
>   # Now unmount the filesystem, create a new one, mount it and try to apply
>   # both send streams to recreate both snapshots.
>   umount $DEV
> 
>   mkfs.btrfs -f $DEV >/dev/null
> 
>   mount $DEV $MNT
> 
>   btrfs receive -f /tmp/snap1.send $MNT
>   btrfs receive -f /tmp/snap2.send $MNT
> 
>   umount $MNT
> 
> When running the test, the receive operation for the incremental stream
> fails:
> 
>   $ ./test-send-rmdir.sh
>   Create a readonly snapshot of '/mnt/sdi' in '/mnt/sdi/snap1'
>   At subvol /mnt/sdi/snap1
>   Create a readonly snapshot of '/mnt/sdi' in '/mnt/sdi/snap2'
>   At subvol /mnt/sdi/snap2
>   At subvol snap1
>   At snapshot snap2
>   ERROR: chown o257-9-0 failed: No such file or directory
> 
> So fix this by tracking directories that have a pending rmdir by inode
> number and generation number, instead of only inode number.
> 
> A test case for fstests follows soon.
> 
> Reported-by: Massimo B. <massimo.b@gmx.net>
> Tested-by: Massimo B. <massimo.b@gmx.net>
> Link: https://lore.kernel.org/linux-btrfs/6ae34776e85912960a253a8327068a892998e685.camel@gmx.net/
> Signed-off-by: Filipe Manana <fdmanana@suse.com>

Added to misc-next, thanks.