Re: [PATCH 3/3] btrfs: test fiemap reports extent as not shared after COWing it in snapshot

[Zorro Lang <zlang@redhat.com>]

On Mon, Oct 31, 2022 at 11:11:21AM +0000, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> Test that if we have a large file, with file extent items spanning several
> leaves in the fs tree, and that is shared due to a snapshot, if we COW one
> of the extents, doing a fiemap will report the respective file range as
> not shared.
> 
> This exercises the processing of delayed references for metadata extents
> in the backref walking code, used by fiemap to determine if an extent is
> shared.
> 
> This used to fail until very recently and was fixed by the following
> kernel commit that landed in 6.1-rc2:
> 
>   943553ef9b51 (""btrfs: fix processing of delayed tree block refs during backref walking")
> 
> Signed-off-by: Filipe Manana <fdmanana@suse.com>
> ---

Good to me,
Reviewed-by: Zorro Lang <zlang@redhat.com>

>  tests/btrfs/280     | 64 +++++++++++++++++++++++++++++++++++++++++++++
>  tests/btrfs/280.out | 21 +++++++++++++++
>  2 files changed, 85 insertions(+)
>  create mode 100755 tests/btrfs/280
>  create mode 100644 tests/btrfs/280.out
> 
> diff --git a/tests/btrfs/280 b/tests/btrfs/280
> new file mode 100755
> index 00000000..06ef221e
> --- /dev/null
> +++ b/tests/btrfs/280
> @@ -0,0 +1,64 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (C) 2022 SUSE Linux Products GmbH. All Rights Reserved.
> +#
> +# FS QA Test 280
> +#
> +# Test that if we have a large file, with file extent items spanning several
> +# leaves in the fs tree, and that is shared due to a snapshot, if we COW one of
> +# the extents, doing a fiemap will report the respective file range as not
> +# shared.
> +#
> +# This exercises the processing of delayed references for metadata extents in
> +# the backref walking code, used by fiemap to determine if an extent is shared.
> +#
> +. ./common/preamble
> +_begin_fstest auto quick compress snapshot fiemap
> +
> +. ./common/filter
> +. ./common/punch # for _filter_fiemap_flags
> +
> +_supported_fs btrfs
> +_require_scratch
> +_require_xfs_io_command "fiemap"
> +
> +_fixed_by_kernel_commit 943553ef9b51 \
> +	"btrfs: fix processing of delayed tree block refs during backref walking"
> +
> +_scratch_mkfs >> $seqres.full 2>&1
> +# We use compression because it's a very quick way to create a file with a very
> +# large number of extents (compression limits the maximum extent size to 128K)
> +# and while using very little disk space.
> +_scratch_mount -o compress
> +
> +# A 128M file full of compressed extents results in a fs tree with a heigth
> +# of 2 (root at level 1), so we'll end up with tree block references in the
> +# extent tree (if the root was a leaf, we would have only data references).
> +$XFS_IO_PROG -f -c "pwrite -b 1M 0 128M" $SCRATCH_MNT/foo | _filter_xfs_io
> +
> +# Create a RW snapshot of the default subvolume.
> +$BTRFS_UTIL_PROG subvolume snapshot $SCRATCH_MNT $SCRATCH_MNT/snap | _filter_scratch
> +
> +echo
> +echo "File foo fiemap before COWing extent:"
> +echo
> +$XFS_IO_PROG -c "fiemap -v" $SCRATCH_MNT/foo | _filter_fiemap_flags
> +
> +echo
> +echo "Overwriting file range [120M, 120M + 128K) in the snapshot"
> +echo
> +$XFS_IO_PROG -c "pwrite -b 128K 120M 128K" $SCRATCH_MNT/snap/foo | _filter_xfs_io
> +# Now fsync the file to force COWing the extent and the path from the root of
> +# the snapshot tree down to the leaf where the extent is at.
> +$XFS_IO_PROG -c "fsync" $SCRATCH_MNT/snap/foo
> +
> +echo
> +echo "File foo fiemap after COWing extent in the snapshot:"
> +echo
> +# Now we should have all extents marked as shared except the 128K extent in the
> +# file range [120M, 120M + 128K).
> +$XFS_IO_PROG -c "fiemap -v" $SCRATCH_MNT/foo | _filter_fiemap_flags
> +
> +# success, all done
> +status=0
> +exit
> diff --git a/tests/btrfs/280.out b/tests/btrfs/280.out
> new file mode 100644
> index 00000000..c3f82966
> --- /dev/null
> +++ b/tests/btrfs/280.out
> @@ -0,0 +1,21 @@
> +QA output created by 280
> +wrote 134217728/134217728 bytes at offset 0
> +XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> +Create a snapshot of 'SCRATCH_MNT' in 'SCRATCH_MNT/snap'
> +
> +File foo fiemap before COWing extent:
> +
> +0: [0..261887]: shared
> +1: [261888..262143]: shared|last
> +
> +Overwriting file range [120M, 120M + 128K) in the snapshot
> +
> +wrote 131072/131072 bytes at offset 125829120
> +XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> +
> +File foo fiemap after COWing extent in the snapshot:
> +
> +0: [0..245759]: shared
> +1: [245760..246015]: none
> +2: [246016..261887]: shared
> +3: [261888..262143]: shared|last
> -- 
> 2.35.1
>