From 72610b1b40005fa19a107ea62b8bcc0ca84ef11b Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Thu, 10 Aug 2017 22:54:51 +0100 Subject: [PATCH] Btrfs: incremental send, fix emission of invalid clone operations When doing an incremental send it's possible that the computed send stream contains clone operations that will fail on the receiver if the receiver has compression enabled and the clone operations target a sector sized extent that starts at a zero file offset, is not compressed on the source filesystem but ends up being compressed and inlined at the destination filesystem. Example scenario: $ mkfs.btrfs -f /dev/sdb $ mount -o compress /dev/sdb /mnt # By doing a direct IO write, the data is not compressed. $ xfs_io -f -d -c "pwrite -S 0xab 0 4K" /mnt/foobar $ btrfs subvolume snapshot -r /mnt /mnt/mysnap1 $ xfs_io -c "reflink /mnt/foobar 0 8K 4K" /mnt/foobar $ btrfs subvolume snapshot -r /mnt /mnt/mysnap2 $ btrfs send -f /tmp/1.snap /mnt/mysnap1 $ btrfs send -f /tmp/2.snap -p /mnt/mysnap1 /mnt/mysnap2 $ umount /mnt $ mkfs.btrfs -f /dev/sdc $ mount -o compress /dev/sdc /mnt $ btrfs receive -f /tmp/1.snap /mnt $ btrfs receive -f /tmp/2.snap /mnt ERROR: failed to clone extents to foobar Operation not supported The same could be achieved by mounting the source filesystem without compression and doing a buffered IO write instead of a direct IO one, and mounting the destination filesystem with compression enabled. So fix this by issuing regular write operations in the send stream instead of clone operations when the source offset is zero and the range has a length matching the sector size. Signed-off-by: Filipe Manana Reviewed-by: Liu Bo Signed-off-by: Chris Mason Signed-off-by: David Sterba --- fs/btrfs/send.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c index 59fb1ed6ca20..8f1d3d6e7087 100644 --- a/fs/btrfs/send.c +++ b/fs/btrfs/send.c @@ -4992,6 +4992,25 @@ static int clone_range(struct send_ctx *sctx, struct btrfs_key key; int ret; + /* + * Prevent cloning from a zero offset with a length matching the sector + * size because in some scenarios this will make the receiver fail. + * + * For example, if in the source filesystem the extent at offset 0 + * has a length of sectorsize and it was written using direct IO, then + * it can never be an inline extent (even if compression is enabled). + * Then this extent can be cloned in the original filesystem to a non + * zero file offset, but it may not be possible to clone in the + * destination filesystem because it can be inlined due to compression + * on the destination filesystem (as the receiver's write operations are + * always done using buffered IO). The same happens when the original + * filesystem does not have compression enabled but the destination + * filesystem has. + */ + if (clone_root->offset == 0 && + len == sctx->send_root->fs_info->sectorsize) + return send_extent_data(sctx, offset, len); + path = alloc_path_for_send(); if (!path) return -ENOMEM; -- 2.20.1