On Thu, Aug 10, 2017 at 10:54:51PM +0100, fdmanana@xxxxxxxxxx wrote: > From: Filipe Manana <fdmanana@xxxxxxxx> > > 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. Reviewed-by: Liu Bo <bo.li.liu@xxxxxxxxxx> Thanks, -liubo > > Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx> > --- > fs/btrfs/send.c | 19 +++++++++++++++++++ > 1 file changed, 19 insertions(+) > > diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c > index b082210df9c8..460be72ab78b 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; > -- > 2.11.0 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
