diff mbox series

btrfs: test creating a snapshot after RWF_NOWAIT write works as expected

Message ID 20200615175028.15090-1-fdmanana@kernel.org (mailing list archive)
State New, archived
Headers show
Series btrfs: test creating a snapshot after RWF_NOWAIT write works as expected | expand

Commit Message

Filipe Manana June 15, 2020, 5:50 p.m. UTC
From: Filipe Manana <fdmanana@suse.com>

Test that creating a snapshot after writing to a file using a RWF_NOWAIT
works, does not hang the snapshot creation task, and we are able to read
the data after.

Currently btrfs hangs when creating the snapshot due to a missing unlock
of a snapshot lock, but it is fixed by a patch with the following subject:

  "btrfs: fix hang on snapshot creation after RWF_NOWAIT write"

Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 tests/btrfs/214     | 66 +++++++++++++++++++++++++++++++++++++++++++++
 tests/btrfs/214.out | 14 ++++++++++
 tests/btrfs/group   |  1 +
 3 files changed, 81 insertions(+)
 create mode 100755 tests/btrfs/214
 create mode 100644 tests/btrfs/214.out

Comments

Eryu Guan July 19, 2020, 4:44 p.m. UTC | #1
On Mon, Jun 15, 2020 at 06:50:28PM +0100, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> Test that creating a snapshot after writing to a file using a RWF_NOWAIT
> works, does not hang the snapshot creation task, and we are able to read
> the data after.
> 
> Currently btrfs hangs when creating the snapshot due to a missing unlock
> of a snapshot lock, but it is fixed by a patch with the following subject:
> 
>   "btrfs: fix hang on snapshot creation after RWF_NOWAIT write"
> 
> Signed-off-by: Filipe Manana <fdmanana@suse.com>

So sorry for the late review.. But I hit the following failure with
v5.8-rc5 kernel, which contains the mentioned fix

 QA output created by 215
 wrote 65536/65536 bytes at offset 0
 XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-wrote 65536/65536 bytes at offset 0
-XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+pwrite: Input/output error
 Create a readonly snapshot of 'SCRATCH_MNT' in 'SCRATCH_MNT/snap'
 File data in the subvolume:
-0000000 fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
+0000000 ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab
 *
 0065536
 File data in the snapshot:
-0000000 fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
+0000000 ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab
 *
 0065536

And I did hit hang when testing without the fix. Is this something that
should be fixed in the test?

Thanks,
Eryu

> ---
>  tests/btrfs/214     | 66 +++++++++++++++++++++++++++++++++++++++++++++
>  tests/btrfs/214.out | 14 ++++++++++
>  tests/btrfs/group   |  1 +
>  3 files changed, 81 insertions(+)
>  create mode 100755 tests/btrfs/214
>  create mode 100644 tests/btrfs/214.out
> 
> diff --git a/tests/btrfs/214 b/tests/btrfs/214
> new file mode 100755
> index 00000000..c835e844
> --- /dev/null
> +++ b/tests/btrfs/214
> @@ -0,0 +1,66 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (C) 2020 SUSE Linux Products GmbH. All Rights Reserved.
> +#
> +# FSQA Test No. 214
> +#
> +# Test that creating a snapshot after writing to a file using a RWF_NOWAIT
> +# works, does not hang the snapshot creation task, and we are able to read
> +# the data after.
> +#
> +seq=`basename $0`
> +seqres=$RESULT_DIR/$seq
> +echo "QA output created by $seq"
> +tmp=/tmp/$$
> +status=1	# failure is the default!
> +trap "_cleanup; exit \$status" 0 1 2 3 15
> +
> +_cleanup()
> +{
> +	cd /
> +	rm -f $tmp.*
> +}
> +
> +# get standard environment, filters and checks
> +. ./common/rc
> +. ./common/filter
> +. ./common/attr
> +
> +# real QA test starts here
> +_supported_fs btrfs
> +_supported_os Linux
> +_require_scratch
> +_require_odirect
> +_require_xfs_io_command pwrite -N
> +_require_chattr C
> +
> +rm -f $seqres.full
> +
> +_scratch_mkfs >>$seqres.full 2>&1
> +_scratch_mount
> +
> +# RWF_NOWAIT writes require NOCOW
> +touch $SCRATCH_MNT/f
> +$CHATTR_PROG +C $SCRATCH_MNT/f
> +
> +$XFS_IO_PROG -d -c "pwrite -S 0xab 0 64K" $SCRATCH_MNT/f | _filter_xfs_io
> +
> +# Now do a WEF_WRITE into a range containing a NOCOWable extent.
> +$XFS_IO_PROG -d -c "pwrite -N -V 1 -S 0xfe 0 64K" $SCRATCH_MNT/f \
> +	| _filter_xfs_io
> +
> +$BTRFS_UTIL_PROG subvolume snapshot -r $SCRATCH_MNT $SCRATCH_MNT/snap \
> +	| _filter_scratch
> +
> +# Unmount, mount again and verify the file in the subvolume and snapshot has
> +# the correct data.
> +_scratch_cycle_mount
> +
> +echo "File data in the subvolume:"
> +od -A d -t x1 $SCRATCH_MNT/f
> +
> +echo "File data in the snapshot:"
> +od -A d -t x1 $SCRATCH_MNT/snap/f
> +
> +status=0
> +exit
> diff --git a/tests/btrfs/214.out b/tests/btrfs/214.out
> new file mode 100644
> index 00000000..6cc66972
> --- /dev/null
> +++ b/tests/btrfs/214.out
> @@ -0,0 +1,14 @@
> +QA output created by 214
> +wrote 65536/65536 bytes at offset 0
> +XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> +wrote 65536/65536 bytes at offset 0
> +XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> +Create a readonly snapshot of 'SCRATCH_MNT' in 'SCRATCH_MNT/snap'
> +File data in the subvolume:
> +0000000 fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
> +*
> +0065536
> +File data in the snapshot:
> +0000000 fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
> +*
> +0065536
> diff --git a/tests/btrfs/group b/tests/btrfs/group
> index 9e48ecc1..a3706e7d 100644
> --- a/tests/btrfs/group
> +++ b/tests/btrfs/group
> @@ -216,3 +216,4 @@
>  211 auto quick log prealloc
>  212 auto balance dangerous
>  213 auto balance dangerous
> +214 auto quick snapshot
> -- 
> 2.26.2
Filipe Manana July 19, 2020, 6:23 p.m. UTC | #2
On Sun, Jul 19, 2020 at 5:44 PM Eryu Guan <guan@eryu.me> wrote:
>
> On Mon, Jun 15, 2020 at 06:50:28PM +0100, fdmanana@kernel.org wrote:
> > From: Filipe Manana <fdmanana@suse.com>
> >
> > Test that creating a snapshot after writing to a file using a RWF_NOWAIT
> > works, does not hang the snapshot creation task, and we are able to read
> > the data after.
> >
> > Currently btrfs hangs when creating the snapshot due to a missing unlock
> > of a snapshot lock, but it is fixed by a patch with the following subject:
> >
> >   "btrfs: fix hang on snapshot creation after RWF_NOWAIT write"
> >
> > Signed-off-by: Filipe Manana <fdmanana@suse.com>
>
> So sorry for the late review.. But I hit the following failure with
> v5.8-rc5 kernel, which contains the mentioned fix
>
>  QA output created by 215
>  wrote 65536/65536 bytes at offset 0
>  XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> -wrote 65536/65536 bytes at offset 0
> -XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> +pwrite: Input/output error
>  Create a readonly snapshot of 'SCRATCH_MNT' in 'SCRATCH_MNT/snap'
>  File data in the subvolume:
> -0000000 fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
> +0000000 ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab
>  *
>  0065536
>  File data in the snapshot:
> -0000000 fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
> +0000000 ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab
>  *
>  0065536
>
> And I did hit hang when testing without the fix. Is this something that
> should be fixed in the test?

Odd.

Works for me on 5.8-rc5:

$ ./check btrfs/215
FSTYP         -- btrfs
PLATFORM      -- Linux/x86_64 debian9 5.8.0-rc5-btrfs-next-63 #1 SMP
PREEMPT Sun Jul 19 17:53:27 WEST 2020
MKFS_OPTIONS  -- /dev/sdb
MOUNT_OPTIONS -- /dev/sdb /home/fdmanana/btrfs-tests/scratch_1

btrfs/215 1s
Ran: btrfs/215
Passed all 1 tests

Is there anything in dmesg?



>
> Thanks,
> Eryu
>
> > ---
> >  tests/btrfs/214     | 66 +++++++++++++++++++++++++++++++++++++++++++++
> >  tests/btrfs/214.out | 14 ++++++++++
> >  tests/btrfs/group   |  1 +
> >  3 files changed, 81 insertions(+)
> >  create mode 100755 tests/btrfs/214
> >  create mode 100644 tests/btrfs/214.out
> >
> > diff --git a/tests/btrfs/214 b/tests/btrfs/214
> > new file mode 100755
> > index 00000000..c835e844
> > --- /dev/null
> > +++ b/tests/btrfs/214
> > @@ -0,0 +1,66 @@
> > +#! /bin/bash
> > +# SPDX-License-Identifier: GPL-2.0
> > +# Copyright (C) 2020 SUSE Linux Products GmbH. All Rights Reserved.
> > +#
> > +# FSQA Test No. 214
> > +#
> > +# Test that creating a snapshot after writing to a file using a RWF_NOWAIT
> > +# works, does not hang the snapshot creation task, and we are able to read
> > +# the data after.
> > +#
> > +seq=`basename $0`
> > +seqres=$RESULT_DIR/$seq
> > +echo "QA output created by $seq"
> > +tmp=/tmp/$$
> > +status=1     # failure is the default!
> > +trap "_cleanup; exit \$status" 0 1 2 3 15
> > +
> > +_cleanup()
> > +{
> > +     cd /
> > +     rm -f $tmp.*
> > +}
> > +
> > +# get standard environment, filters and checks
> > +. ./common/rc
> > +. ./common/filter
> > +. ./common/attr
> > +
> > +# real QA test starts here
> > +_supported_fs btrfs
> > +_supported_os Linux
> > +_require_scratch
> > +_require_odirect
> > +_require_xfs_io_command pwrite -N
> > +_require_chattr C
> > +
> > +rm -f $seqres.full
> > +
> > +_scratch_mkfs >>$seqres.full 2>&1
> > +_scratch_mount
> > +
> > +# RWF_NOWAIT writes require NOCOW
> > +touch $SCRATCH_MNT/f
> > +$CHATTR_PROG +C $SCRATCH_MNT/f
> > +
> > +$XFS_IO_PROG -d -c "pwrite -S 0xab 0 64K" $SCRATCH_MNT/f | _filter_xfs_io
> > +
> > +# Now do a WEF_WRITE into a range containing a NOCOWable extent.
> > +$XFS_IO_PROG -d -c "pwrite -N -V 1 -S 0xfe 0 64K" $SCRATCH_MNT/f \
> > +     | _filter_xfs_io
> > +
> > +$BTRFS_UTIL_PROG subvolume snapshot -r $SCRATCH_MNT $SCRATCH_MNT/snap \
> > +     | _filter_scratch
> > +
> > +# Unmount, mount again and verify the file in the subvolume and snapshot has
> > +# the correct data.
> > +_scratch_cycle_mount
> > +
> > +echo "File data in the subvolume:"
> > +od -A d -t x1 $SCRATCH_MNT/f
> > +
> > +echo "File data in the snapshot:"
> > +od -A d -t x1 $SCRATCH_MNT/snap/f
> > +
> > +status=0
> > +exit
> > diff --git a/tests/btrfs/214.out b/tests/btrfs/214.out
> > new file mode 100644
> > index 00000000..6cc66972
> > --- /dev/null
> > +++ b/tests/btrfs/214.out
> > @@ -0,0 +1,14 @@
> > +QA output created by 214
> > +wrote 65536/65536 bytes at offset 0
> > +XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> > +wrote 65536/65536 bytes at offset 0
> > +XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> > +Create a readonly snapshot of 'SCRATCH_MNT' in 'SCRATCH_MNT/snap'
> > +File data in the subvolume:
> > +0000000 fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
> > +*
> > +0065536
> > +File data in the snapshot:
> > +0000000 fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
> > +*
> > +0065536
> > diff --git a/tests/btrfs/group b/tests/btrfs/group
> > index 9e48ecc1..a3706e7d 100644
> > --- a/tests/btrfs/group
> > +++ b/tests/btrfs/group
> > @@ -216,3 +216,4 @@
> >  211 auto quick log prealloc
> >  212 auto balance dangerous
> >  213 auto balance dangerous
> > +214 auto quick snapshot
> > --
> > 2.26.2
Eryu Guan July 19, 2020, 6:45 p.m. UTC | #3
On Sun, Jul 19, 2020 at 07:23:53PM +0100, Filipe Manana wrote:
> On Sun, Jul 19, 2020 at 5:44 PM Eryu Guan <guan@eryu.me> wrote:
> >
> > On Mon, Jun 15, 2020 at 06:50:28PM +0100, fdmanana@kernel.org wrote:
> > > From: Filipe Manana <fdmanana@suse.com>
> > >
> > > Test that creating a snapshot after writing to a file using a RWF_NOWAIT
> > > works, does not hang the snapshot creation task, and we are able to read
> > > the data after.
> > >
> > > Currently btrfs hangs when creating the snapshot due to a missing unlock
> > > of a snapshot lock, but it is fixed by a patch with the following subject:
> > >
> > >   "btrfs: fix hang on snapshot creation after RWF_NOWAIT write"
> > >
> > > Signed-off-by: Filipe Manana <fdmanana@suse.com>
> >
> > So sorry for the late review.. But I hit the following failure with
> > v5.8-rc5 kernel, which contains the mentioned fix
> >
> >  QA output created by 215
> >  wrote 65536/65536 bytes at offset 0
> >  XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> > -wrote 65536/65536 bytes at offset 0
> > -XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> > +pwrite: Input/output error
> >  Create a readonly snapshot of 'SCRATCH_MNT' in 'SCRATCH_MNT/snap'
> >  File data in the subvolume:
> > -0000000 fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
> > +0000000 ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab
> >  *
> >  0065536
> >  File data in the snapshot:
> > -0000000 fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
> > +0000000 ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab
> >  *
> >  0065536
> >
> > And I did hit hang when testing without the fix. Is this something that
> > should be fixed in the test?
> 
> Odd.
> 
> Works for me on 5.8-rc5:
> 
> $ ./check btrfs/215
> FSTYP         -- btrfs
> PLATFORM      -- Linux/x86_64 debian9 5.8.0-rc5-btrfs-next-63 #1 SMP
> PREEMPT Sun Jul 19 17:53:27 WEST 2020
> MKFS_OPTIONS  -- /dev/sdb
> MOUNT_OPTIONS -- /dev/sdb /home/fdmanana/btrfs-tests/scratch_1
> 
> btrfs/215 1s
> Ran: btrfs/215
> Passed all 1 tests
> 
> Is there anything in dmesg?

Hmm, there is a dio failure message.

[ 8077.648741] run fstests btrfs/216 at 2020-07-20 02:42:37
[ 8078.169516] BTRFS: device fsid 0de433a0-628f-4f7c-bb81-a9632d690d0f devid 1 transid 5 /dev/mapper/testvg-lv2 scanned by mkfs.btrfs (76661)
[ 8078.199269] BTRFS info (device dm-5): disk space caching is enabled
[ 8078.200897] BTRFS info (device dm-5): has skinny extents
[ 8078.202227] BTRFS info (device dm-5): flagging fs with big metadata feature
[ 8078.208853] BTRFS info (device dm-5): checking UUID tree
[ 8078.231519] BTRFS warning (device dm-5): direct IO failed ino 257 rw 1,2131969 sector 0x6800 len 4096 err no 10
[ 8078.357124] BTRFS info (device dm-5): disk space caching is enabled
[ 8078.357906] BTRFS info (device dm-5): has skinny extents

My kernel version and btrfs-progs version

[root@fedoravm xfstests]# uname -a
Linux fedoravm 5.8.0-rc5 #52 SMP Mon Jul 20 00:25:44 CST 2020 x86_64 x86_64 x86_64 GNU/Linux
[root@fedoravm xfstests]# btrfs --version
btrfs-progs v5.4

Thanks,
Eryu

> 
> 
> 
> >
> > Thanks,
> > Eryu
> >
> > > ---
> > >  tests/btrfs/214     | 66 +++++++++++++++++++++++++++++++++++++++++++++
> > >  tests/btrfs/214.out | 14 ++++++++++
> > >  tests/btrfs/group   |  1 +
> > >  3 files changed, 81 insertions(+)
> > >  create mode 100755 tests/btrfs/214
> > >  create mode 100644 tests/btrfs/214.out
> > >
> > > diff --git a/tests/btrfs/214 b/tests/btrfs/214
> > > new file mode 100755
> > > index 00000000..c835e844
> > > --- /dev/null
> > > +++ b/tests/btrfs/214
> > > @@ -0,0 +1,66 @@
> > > +#! /bin/bash
> > > +# SPDX-License-Identifier: GPL-2.0
> > > +# Copyright (C) 2020 SUSE Linux Products GmbH. All Rights Reserved.
> > > +#
> > > +# FSQA Test No. 214
> > > +#
> > > +# Test that creating a snapshot after writing to a file using a RWF_NOWAIT
> > > +# works, does not hang the snapshot creation task, and we are able to read
> > > +# the data after.
> > > +#
> > > +seq=`basename $0`
> > > +seqres=$RESULT_DIR/$seq
> > > +echo "QA output created by $seq"
> > > +tmp=/tmp/$$
> > > +status=1     # failure is the default!
> > > +trap "_cleanup; exit \$status" 0 1 2 3 15
> > > +
> > > +_cleanup()
> > > +{
> > > +     cd /
> > > +     rm -f $tmp.*
> > > +}
> > > +
> > > +# get standard environment, filters and checks
> > > +. ./common/rc
> > > +. ./common/filter
> > > +. ./common/attr
> > > +
> > > +# real QA test starts here
> > > +_supported_fs btrfs
> > > +_supported_os Linux
> > > +_require_scratch
> > > +_require_odirect
> > > +_require_xfs_io_command pwrite -N
> > > +_require_chattr C
> > > +
> > > +rm -f $seqres.full
> > > +
> > > +_scratch_mkfs >>$seqres.full 2>&1
> > > +_scratch_mount
> > > +
> > > +# RWF_NOWAIT writes require NOCOW
> > > +touch $SCRATCH_MNT/f
> > > +$CHATTR_PROG +C $SCRATCH_MNT/f
> > > +
> > > +$XFS_IO_PROG -d -c "pwrite -S 0xab 0 64K" $SCRATCH_MNT/f | _filter_xfs_io
> > > +
> > > +# Now do a WEF_WRITE into a range containing a NOCOWable extent.
> > > +$XFS_IO_PROG -d -c "pwrite -N -V 1 -S 0xfe 0 64K" $SCRATCH_MNT/f \
> > > +     | _filter_xfs_io
> > > +
> > > +$BTRFS_UTIL_PROG subvolume snapshot -r $SCRATCH_MNT $SCRATCH_MNT/snap \
> > > +     | _filter_scratch
> > > +
> > > +# Unmount, mount again and verify the file in the subvolume and snapshot has
> > > +# the correct data.
> > > +_scratch_cycle_mount
> > > +
> > > +echo "File data in the subvolume:"
> > > +od -A d -t x1 $SCRATCH_MNT/f
> > > +
> > > +echo "File data in the snapshot:"
> > > +od -A d -t x1 $SCRATCH_MNT/snap/f
> > > +
> > > +status=0
> > > +exit
> > > diff --git a/tests/btrfs/214.out b/tests/btrfs/214.out
> > > new file mode 100644
> > > index 00000000..6cc66972
> > > --- /dev/null
> > > +++ b/tests/btrfs/214.out
> > > @@ -0,0 +1,14 @@
> > > +QA output created by 214
> > > +wrote 65536/65536 bytes at offset 0
> > > +XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> > > +wrote 65536/65536 bytes at offset 0
> > > +XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> > > +Create a readonly snapshot of 'SCRATCH_MNT' in 'SCRATCH_MNT/snap'
> > > +File data in the subvolume:
> > > +0000000 fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
> > > +*
> > > +0065536
> > > +File data in the snapshot:
> > > +0000000 fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
> > > +*
> > > +0065536
> > > diff --git a/tests/btrfs/group b/tests/btrfs/group
> > > index 9e48ecc1..a3706e7d 100644
> > > --- a/tests/btrfs/group
> > > +++ b/tests/btrfs/group
> > > @@ -216,3 +216,4 @@
> > >  211 auto quick log prealloc
> > >  212 auto balance dangerous
> > >  213 auto balance dangerous
> > > +214 auto quick snapshot
> > > --
> > > 2.26.2
diff mbox series

Patch

diff --git a/tests/btrfs/214 b/tests/btrfs/214
new file mode 100755
index 00000000..c835e844
--- /dev/null
+++ b/tests/btrfs/214
@@ -0,0 +1,66 @@ 
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2020 SUSE Linux Products GmbH. All Rights Reserved.
+#
+# FSQA Test No. 214
+#
+# Test that creating a snapshot after writing to a file using a RWF_NOWAIT
+# works, does not hang the snapshot creation task, and we are able to read
+# the data after.
+#
+seq=`basename $0`
+seqres=$RESULT_DIR/$seq
+echo "QA output created by $seq"
+tmp=/tmp/$$
+status=1	# failure is the default!
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+_cleanup()
+{
+	cd /
+	rm -f $tmp.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+. ./common/attr
+
+# real QA test starts here
+_supported_fs btrfs
+_supported_os Linux
+_require_scratch
+_require_odirect
+_require_xfs_io_command pwrite -N
+_require_chattr C
+
+rm -f $seqres.full
+
+_scratch_mkfs >>$seqres.full 2>&1
+_scratch_mount
+
+# RWF_NOWAIT writes require NOCOW
+touch $SCRATCH_MNT/f
+$CHATTR_PROG +C $SCRATCH_MNT/f
+
+$XFS_IO_PROG -d -c "pwrite -S 0xab 0 64K" $SCRATCH_MNT/f | _filter_xfs_io
+
+# Now do a WEF_WRITE into a range containing a NOCOWable extent.
+$XFS_IO_PROG -d -c "pwrite -N -V 1 -S 0xfe 0 64K" $SCRATCH_MNT/f \
+	| _filter_xfs_io
+
+$BTRFS_UTIL_PROG subvolume snapshot -r $SCRATCH_MNT $SCRATCH_MNT/snap \
+	| _filter_scratch
+
+# Unmount, mount again and verify the file in the subvolume and snapshot has
+# the correct data.
+_scratch_cycle_mount
+
+echo "File data in the subvolume:"
+od -A d -t x1 $SCRATCH_MNT/f
+
+echo "File data in the snapshot:"
+od -A d -t x1 $SCRATCH_MNT/snap/f
+
+status=0
+exit
diff --git a/tests/btrfs/214.out b/tests/btrfs/214.out
new file mode 100644
index 00000000..6cc66972
--- /dev/null
+++ b/tests/btrfs/214.out
@@ -0,0 +1,14 @@ 
+QA output created by 214
+wrote 65536/65536 bytes at offset 0
+XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+wrote 65536/65536 bytes at offset 0
+XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+Create a readonly snapshot of 'SCRATCH_MNT' in 'SCRATCH_MNT/snap'
+File data in the subvolume:
+0000000 fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
+*
+0065536
+File data in the snapshot:
+0000000 fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
+*
+0065536
diff --git a/tests/btrfs/group b/tests/btrfs/group
index 9e48ecc1..a3706e7d 100644
--- a/tests/btrfs/group
+++ b/tests/btrfs/group
@@ -216,3 +216,4 @@ 
 211 auto quick log prealloc
 212 auto balance dangerous
 213 auto balance dangerous
+214 auto quick snapshot