Re: [PATCH] btrfs: test fallocate against a file range with a mix of holes and extents

["Darrick J. Wong" <djwong@kernel.org>]

On Thu, Mar 17, 2022 at 03:03:40PM +0000, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> Test that if we call fallocate against a file range that has a mix of holes
> and written extents, the fallocate succeeds if the filesystem has enough free
> space to allocate extents for the holes.
> 
> This currently fails on btrfs and is fixed by a patch that has the subject:
> 
>   "btrfs: only reserve the needed data space amount during fallocate"
> 
> There's nothing that is really specific to btrfs in the test case, and the
> same test passes on ext4 and f2fs for example. But it fails on xfs, and
> after some discussion with Darrick, it seems it's due to technical reasons
> that would require a significant effort to xfs's implementation, and at
> the moment there isn't enough motivation to do such change. The relevent
> thread is at:
> 
>    https://lore.kernel.org/linux-btrfs/20220315164011.GF8241@magnolia/
> 
> So for the time being, make the test btrfs specific.
> 
> Signed-off-by: Filipe Manana <fdmanana@suse.com>
> ---
>  tests/btrfs/261     | 58 +++++++++++++++++++++++++++++++++++++++++++++
>  tests/btrfs/261.out | 20 ++++++++++++++++
>  2 files changed, 78 insertions(+)
>  create mode 100755 tests/btrfs/261
>  create mode 100644 tests/btrfs/261.out
> 
> diff --git a/tests/btrfs/261 b/tests/btrfs/261
> new file mode 100755
> index 00000000..e7e9f15e
> --- /dev/null
> +++ b/tests/btrfs/261
> @@ -0,0 +1,58 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2022 SUSE Linux Products GmbH.  All Rights Reserved.
> +#
> +# FS QA Test 261
> +#
> +# Test that if we call fallocate against a large file range that is nearly full
> +# with written extents, the fallocate succeeds and allocates unwritten extents
> +# for the holes in the range.
> +#
> +. ./common/preamble
> +_begin_fstest auto quick prealloc
> +
> +. ./common/rc
> +. ./common/filter
> +. ./common/punch
> +
> +# real QA test starts here
> +
> +_supported_fs btrfs

Or make this a generic test and add:

test $FSTYP == "xfs"  && _notrun "xfs doesn't work that way lol"

> +_require_scratch
> +_require_xfs_io_command "falloc"
> +_require_xfs_io_command "fiemap"
> +
> +rm -f $seqres.full
> +
> +# Create a 1G filesystem.
> +_scratch_mkfs_sized $((1024 * 1024 * 1024)) >>$seqres.full 2>&1
> +_scratch_mount
> +
> +# Create a file with a size of 600M and two holes, each with a size of 1M and
> +# at file ranges [200, 201M[ and [401M, 402M[.
> +$XFS_IO_PROG -f -c "pwrite -S 0xab 0 200M" \
> +                -c "pwrite -S 0xcd 201M 200M" \
> +                -c "pwrite -S 0xef 402M 198M" \
> +		$SCRATCH_MNT/foobar | _filter_xfs_io
> +
> +# Now call fallocate against the whole file range.
> +# It should succeed, because only 2M of data space needs to be allocated,
> +# and not 600M (which isn't available since our fs has a size of 1G).
> +$XFS_IO_PROG -c "falloc 0 600M" $SCRATCH_MNT/foobar
> +
> +# Unmount and mount again the filesystem. We want to veriy that the fallocate

'verify'

Other than those two things, this test looks sound to me.

--D

> +# results were persisted and that all the file metadata and data on disk are
> +# also correct.
> +_scratch_cycle_mount
> +
> +echo -n "Number of unwritten extents in the file: "
> +$XFS_IO_PROG -c "fiemap -v" $SCRATCH_MNT/foobar | _filter_fiemap | \
> +    grep 'unwritten' | wc -l
> +
> +# Verify we don't have any corruption caused by the fallocate.
> +echo "File content after fallocate:"
> +od -A d -t x1 $SCRATCH_MNT/foobar
> +
> +# success, all done
> +status=0
> +exit
> diff --git a/tests/btrfs/261.out b/tests/btrfs/261.out
> new file mode 100644
> index 00000000..db7f0d6d
> --- /dev/null
> +++ b/tests/btrfs/261.out
> @@ -0,0 +1,20 @@
> +QA output created by 261
> +wrote 209715200/209715200 bytes at offset 0
> +XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> +wrote 209715200/209715200 bytes at offset 210763776
> +XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> +wrote 207618048/207618048 bytes at offset 421527552
> +XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> +Number of unwritten extents in the file: 2
> +File content after fallocate:
> +0000000 ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab
> +*
> +209715200 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> +*
> +210763776 cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd
> +*
> +420478976 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> +*
> +421527552 ef ef ef ef ef ef ef ef ef ef ef ef ef ef ef ef
> +*
> +629145600
> -- 
> 2.33.0
>