Re: [RFC,2/2] xfstests: common/rc: add cluster size support for ext4

[JeffleXu <jefflexu@linux.alibaba.com>]

Sorry for digging this really old post [1]. The overall background is
that, @offset and @len need to be aligned with cluster size when doing
fallocate(), or several xfstests cases calling fsx will fail if the
tested filesystem enabling 'bigalloc' feature.

On April 27, 2020, 5:33 p.m. UTC Darrick J. Wong wrote:

> On Fri, Apr 24, 2020 at 05:33:50PM +0800, Jeffle Xu wrote:
>> Inserting and collapsing range on ext4 with 'bigalloc' feature will
>> fail due to the offset and size should be alligned with the cluster
>> size.
>> 
>> The previous patch has add support for cluster size in fsx. Detect and
>> pass the cluster size parameter to fsx if the underlying filesystem
>> is ext4 with bigalloc.
>> 
>> Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
>> ---
>>  common/rc | 9 +++++++++
>>  1 file changed, 9 insertions(+)
>> 
>> diff --git a/common/rc b/common/rc
>> index 2000bd9..71dde5f 100644
>> --- a/common/rc
>> +++ b/common/rc
>> @@ -3908,6 +3908,15 @@ run_fsx()
>>  {
>>  	echo fsx $@
>>  	local args=`echo $@ | sed -e "s/ BSIZE / $bsize /g" -e "s/ PSIZE / $psize /g"`
>> +
>> +	if [ "$FSTYP" == "ext4" ]; then
>> +		local cluster_size=$(tune2fs -l $TEST_DEV | grep 'Cluster size' | awk '{print $3}')
>> +		if [ -n $cluster_size ]; then
>> +			echo "cluster size: $cluster_size"
>> +			args="$args -u $cluster_size"
>> +		fi
>> +	fi
> 
> Computing the file allocation block size ought to be a separate helper.
> 
> I wonder if there's a standard way to report cluster sizes, seeing as
> fat, ext4, ocfs2, and xfs can all have minimum space allocation units
> that are larger than the base fs block size.

In fact only for insert_range and collapse range of ext4 and xfs (in
realtime mode), @offset and @len need to be aligned with cluster size.

Though fat and ocfs2 also support cluster size, ocfs2 only supports
preallocate and punch_hole, and fat only supports preallocate, in which
case @offset and @len needn't be aligned with cluster size.


So we need to align @offset and @len with cluster size only for ext4 and
xfs (in realtime mode) at a minimum cost, to fix this issue. But the
question is, there's no standard programming interface exporting cluster
size. For both ext4 and xfs, it's stored as a binary data in disk
version superblock, e.g., tune2fs could detect the cluster size of ext4.


Any idea on how to query the cluster size?


[1]
https://patchwork.kernel.org/project/fstests/cover/1587720830-11955-1-git-send-email-jefflexu@linux.alibaba.com/

-- 
Thanks,
Jeffle