Re: [PATCH] generic: fallocate two bytes at block boundary

[Max Reitz <mreitz@redhat.com>]

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On 26.09.19 17:55, Darrick J. Wong wrote:
> On Thu, Sep 26, 2019 at 05:29:27PM +0200, Max Reitz wrote:
>> Allocating two bytes at a block boundary with fallocate should allocate
>> both blocks involved.  Test this by writing both bytes with dd
>> afterwards and see whether the on-disk size increases (it should not).
>>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>> ---
>>  tests/generic/568     | 63 +++++++++++++++++++++++++++++++++++++++++++
>>  tests/generic/568.out |  2 ++
>>  tests/generic/group   |  1 +
>>  3 files changed, 66 insertions(+)
>>  create mode 100755 tests/generic/568
>>  create mode 100644 tests/generic/568.out
>>
>> diff --git a/tests/generic/568 b/tests/generic/568
>> new file mode 100755
>> index 00000000..8fbdcda0
>> --- /dev/null
>> +++ b/tests/generic/568
>> @@ -0,0 +1,63 @@
>> +#! /bin/bash
>> +# SPDX-License-Identifier: GPL-2.0
>> +# Copyright (c) 2019 Red Hat, Inc.  All Rights Reserved.
>> +#
>> +# FS QA Test No. generic/568
>> +#
>> +# Test that fallocating an unaligned range allocates all blocks
>> +# touched by that range
>> +#
>> +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 "$tmp".*
>> +}
>> +
>> +# get standard environment, filters and checks
>> +. ./common/rc
>> +. ./common/filter
>> +
>> +# real QA test starts here
>> +_supported_fs generic
>> +_supported_os Linux
>> +_require_scratch
>> +
>> +testfile="$SCRATCH_MNT/testfile"
>> +
>> +_scratch_mkfs > /dev/null 2>&1
>> +_scratch_mount
>> +
>> +# Fallocate 2 bytes across a block boundary
>> +block_size=$(stat -fc '%S' "$SCRATCH_MNT")
> 
> block_size=$(_get_file_block_size $SCRATCH_MNT)

Ah, nice.

>> +fallocate -o $((block_size - 1)) -l 2 "$testfile"
> 
> If you're going to use an external program, you need to gate the test on
> whether or not the program's installed, by calling _require_command.

OK.

> Though probably the easier way would be to use xfs_io since fstests
> requires that xfsprogs be installed:
> 
> 	$XFS_IO_PROG -f -c "falloc $((block_size - 1)) 2" $testfile
> 
> Though you do still have to put at the top of the test:
> 
> 	_require_xfs_io_command "falloc"
> 
> Because not all filesystems support fallocate.

So I suppose as long as one doesn’t use special XFS commands, xfs_io is
filesystem-agnostic?

>> +
>> +# Both the first blocks should be allocated now.  Check that by
>> +# inquiring whether the file grows when we write to the two bytes we
>> +# have just fallocated.
>> +
>> +allocated_size_before=$(($(stat -c '%b * %B' "$testfile")))
>> +
>> +dd if=/dev/zero of="$testfile" bs=1 conv=notrunc \
>> +    seek=$((block_size - 1)) count=2 \
>> +    2>&1 | _filter_dd
> 
> $XFS_IO_PROG -c "pwrite $((block_size - 1)) 2" $testfile
> 
>> +
>> +allocated_size_after=$(($(stat -c '%b * %B' "$testfile")))
>> +
>> +if [ $allocated_size_after -gt $allocated_size_before ]; then
>> +	echo "ERROR: File grew from ${allocated_size_before} B to" \
>> +	     "${allocated_size_after} when writing to the fallocated range."
>> +else
>> +	echo "OK: File did not grow."
> 
> Other than that, the logic makes sense to me.  Thanks for writing this
> up!

OK, thanks, I’ll prepare a v2.

Max


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