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Btrfs: send, fix more issues related to directory renames
This is a continuation of the previous changes titled:
Btrfs: fix incremental send's decision to delay a dir move/rename
Btrfs: part 2, fix incremental send's decision to delay a dir move/rename
There's a few more cases where a directory rename/move must be delayed which was
previously overlooked. If our immediate ancestor has a lower inode number than
ours and it doesn't have a delayed rename/move operation associated to it, it
doesn't mean there isn't any non-direct ancestor of our current inode that needs
to be renamed/moved before our current inode (i.e. with a higher inode number
than ours).
So we can't stop the search if our immediate ancestor has a lower inode number than
ours, we need to navigate the directory hierarchy upwards until we hit the root or:
1) find an ancestor with an higher inode number that was renamed/moved in the send
root too (or already has a pending rename/move registered);
2) find an ancestor that is a new directory (higher inode number than ours and
exists only in the send root).
Reproducer for case 1)
$ mkfs.btrfs -f /dev/sdd
$ mount /dev/sdd /mnt
$ mkdir -p /mnt/a/b
$ mkdir -p /mnt/a/c/d
$ mkdir /mnt/a/b/e
$ mkdir /mnt/a/c/d/f
$ mv /mnt/a/b /mnt/a/c/d/2b
$ mkdir /mnt/a/x
$ mkdir /mnt/a/y
$ btrfs subvolume snapshot -r /mnt /mnt/snap1
$ btrfs send /mnt/snap1 -f /tmp/base.send
$ mv /mnt/a/x /mnt/a/y
$ mv /mnt/a/c/d/2b/e /mnt/a/c/d/2b/2e
$ mv /mnt/a/c/d /mnt/a/h/2d
$ mv /mnt/a/c /mnt/a/h/2d/2b/2c
$ btrfs subvolume snapshot -r /mnt /mnt/snap2
$ btrfs send -p /mnt/snap1 /mnt/snap2 -f /tmp/incremental.send
Simple reproducer for case 2)
$ mkfs.btrfs -f /dev/sdd
$ mount /dev/sdd /mnt
$ mkdir -p /mnt/a/b
$ mkdir /mnt/a/c
$ mv /mnt/a/b /mnt/a/c/b2
$ mkdir /mnt/a/e
$ btrfs subvolume snapshot -r /mnt /mnt/snap1
$ btrfs send /mnt/snap1 -f /tmp/base.send
$ mv /mnt/a/c/b2 /mnt/a/e/b3
$ mkdir /mnt/a/e/b3/f
$ mkdir /mnt/a/h
$ mv /mnt/a/c /mnt/a/e/b3/f/c2
$ mv /mnt/a/e /mnt/a/h/e2
$ btrfs subvolume snapshot -r /mnt /mnt/snap2
$ btrfs send -p /mnt/snap1 /mnt/snap2 -f /tmp/incremental.send
Another simple reproducer for case 2)
$ mkfs.btrfs -f /dev/sdd
$ mount /dev/sdd /mnt
$ mkdir -p /mnt/a/b
$ mkdir /mnt/a/c
$ mkdir /mnt/a/b/d
$ mkdir /mnt/a/c/e
$ btrfs subvolume snapshot -r /mnt /mnt/snap1
$ btrfs send /mnt/snap1 -f /tmp/base.send
$ mkdir /mnt/a/b/d/f
$ mkdir /mnt/a/b/g
$ mv /mnt/a/c/e /mnt/a/b/g/e2
$ mv /mnt/a/c /mnt/a/b/d/f/c2
$ mv /mnt/a/b/d/f /mnt/a/b/g/e2/f2
$ btrfs subvolume snapshot -r /mnt /mnt/snap2
$ btrfs send -p /mnt/snap1 /mnt/snap2 -f /tmp/incremental.send
More complex reproducer for case 2)
$ mkfs.btrfs -f /dev/sdd
$ mount /dev/sdd /mnt
$ mkdir -p /mnt/a/b
$ mkdir -p /mnt/a/c/d
$ mkdir /mnt/a/b/e
$ mkdir /mnt/a/c/d/f
$ mv /mnt/a/b /mnt/a/c/d/2b
$ mkdir /mnt/a/x
$ mkdir /mnt/a/y
$ btrfs subvolume snapshot -r /mnt /mnt/snap1
$ btrfs send /mnt/snap1 -f /tmp/base.send
$ mv /mnt/a/x /mnt/a/y
$ mv /mnt/a/c/d/2b/e /mnt/a/c/d/2b/2e
$ mv /mnt/a/c/d /mnt/a/h/2d
$ mv /mnt/a/c /mnt/a/h/2d/2b/2c
$ btrfs subvolume snapshot -r /mnt /mnt/snap2
$ btrfs send -p /mnt/snap1 /mnt/snap2 -f /tmp/incremental.send
For both cases the incremental send would enter an infinite loop when building
path strings.
While solving these cases, this change also re-implements the code to detect
when directory moves/renames should be delayed. Instead of dealing with several
specific cases separately, it's now more generic handling all cases with a simple
detection algorithm and if when applying a delayed move/rename there's a path loop
detected, it further delays the move/rename registering a new ancestor inode as
the dependency inode (so our rename happens after that ancestor is renamed).
Tests for these cases is being added to xfstests too.
Signed-off-by: 
Filipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: Chris Mason <clm@fb.com>