On 2020/1/31 下午12:39, Anand Jain wrote:
> Try to punch hole with unaligned size and offset when the FS is
> full. Mainly holes are punched at locations which are unaligned
> with the file extent boundaries when the FS is full by data.
> As the punching holes at unaligned location will involve
> truncating blocks instead of just dropping the extents, it shall
> involve reserving data and metadata space for delalloc and so data
> alloc fails as the FS is full.

It's better to mention the nocow part.
For COW part, the ENOSPC is still expected.

As that's the main reason I failed to understand the use case.

Thanks,
Qu
> 
> btrfs_punch_hole()
>  btrfs_truncate_block()
>    btrfs_check_data_free_space() <-- ENOSPC
> 
> We don't fail punch hole if the holes are aligned with the file
> extent boundaries as it shall involve just dropping the related
> extents, without truncating data extent blocks.
> 
> Link: https://patchwork.kernel.org/patch/11357415/
> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> Reviewed-by: Filipe Manana <fdmanana@suse.com>
> Signed-off-by: Eryu Guan <guaneryu@gmail.com>
> (cherry picked from commit 4c2c678cd56a81a210cb16f9f9347073e91e2fb0)
> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> 
> Conflicts:
> 	tests/btrfs/group
> ---
> Its decided to bring back this test case, now the problem is better understood
> and the fix is available in the ML as in [Link].
> 
>  tests/btrfs/172     | 73 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  tests/btrfs/172.out |  2 ++
>  tests/btrfs/group   |  1 +
>  3 files changed, 76 insertions(+)
>  create mode 100755 tests/btrfs/172
>  create mode 100644 tests/btrfs/172.out
> 
> diff --git a/tests/btrfs/172 b/tests/btrfs/172
> new file mode 100755
> index 000000000000..0dffb2dff40b
> --- /dev/null
> +++ b/tests/btrfs/172
> @@ -0,0 +1,73 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2018 Oracle. All Rights Reserved.
> +#
> +# FS QA Test 172
> +#
> +# Test if the unaligned (by size and offset) punch hole is successful when FS
> +# is at ENOSPC.
> +#
> +seq=`basename $0`
> +seqres=$RESULT_DIR/$seq
> +echo "QA output created by $seq"
> +
> +here=`pwd`
> +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
> +
> +# remove previous $seqres.full before test
> +rm -f $seqres.full
> +
> +# real QA test starts here
> +
> +# Modify as appropriate.
> +_supported_fs btrfs
> +_supported_os Linux
> +_require_scratch
> +_require_xfs_io_command "fpunch"
> +
> +_scratch_mkfs_sized $((256 * 1024 *1024)) >> $seqres.full
> +
> +# max_inline ensures data is not inlined within metadata extents
> +_scratch_mount "-o max_inline=0,nodatacow"
> +
> +cat /proc/self/mounts | grep $SCRATCH_DEV >> $seqres.full
> +$BTRFS_UTIL_PROG filesystem df $SCRATCH_MNT >> $seqres.full
> +
> +extent_size=$(_scratch_btrfs_sectorsize)
> +unalign_by=512
> +echo extent_size=$extent_size unalign_by=$unalign_by >> $seqres.full
> +
> +$XFS_IO_PROG -f -c "pwrite -S 0xab 0 $((extent_size * 10))" \
> +					$SCRATCH_MNT/testfile >> $seqres.full
> +
> +echo "Fill all space available for data and all unallocated space." >> $seqres.full
> +dd status=none if=/dev/zero of=$SCRATCH_MNT/filler bs=512 >> $seqres.full 2>&1
> +
> +hole_offset=0
> +hole_len=$unalign_by
> +$XFS_IO_PROG -c "fpunch $hole_offset $hole_len" $SCRATCH_MNT/testfile
> +
> +hole_offset=$(($extent_size + $unalign_by))
> +hole_len=$(($extent_size - $unalign_by))
> +$XFS_IO_PROG -c "fpunch $hole_offset $hole_len" $SCRATCH_MNT/testfile
> +
> +hole_offset=$(($extent_size * 2 + $unalign_by))
> +hole_len=$(($extent_size * 5))
> +$XFS_IO_PROG -c "fpunch $hole_offset $hole_len" $SCRATCH_MNT/testfile
> +
> +# success, all done
> +echo "Silence is golden"
> +status=0
> +exit
> diff --git a/tests/btrfs/172.out b/tests/btrfs/172.out
> new file mode 100644
> index 000000000000..ce2de3f0d107
> --- /dev/null
> +++ b/tests/btrfs/172.out
> @@ -0,0 +1,2 @@
> +QA output created by 172
> +Silence is golden
> diff --git a/tests/btrfs/group b/tests/btrfs/group
> index 4b64bf8b6d2f..697b6a38ea00 100644
> --- a/tests/btrfs/group
> +++ b/tests/btrfs/group
> @@ -174,6 +174,7 @@
>  169 auto quick send
>  170 auto quick snapshot
>  171 auto quick qgroup
> +172 auto quick punch
>  173 auto quick swap
>  174 auto quick swap
>  175 auto quick swap volume
>