Re: [PATCH] fstests: Introduce check for explicit SHARED extent flag reporting

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 11/18/2016 01:54 PM, Darrick J. Wong wrote:
> On Thu, Nov 17, 2016 at 10:06:48AM +0800, Qu Wenruo wrote:
>> For fs support reflink, some of them (OK, btrfs again) doesn't split
>> SHARED flag for extent fiemap reporting.
>>
>> For example:
>>   0         4K         8K
>>    / File1: Extent 0  \
>>   /                    \
>>   |<- On disk Extent-->|
>>   |        /
>>   | File2 /
>>     Extent: 0
>>
>> Fs supports explicit SHARED extent reporting should report fiemap like:
>> File1: 2 extents
>> Extent 0-4K: SHARED
>> Extent 4-8K:
>> File2: 1 extents
>> Extent 0-4K: SHARED
>>
>> Fs doesn't support explicit reporting will report fiemap like:
>> File1: 1 extent
>> Extent 0-8K: SHARED
>> File2: 1 extent
>> Extent 0-4K: SHARED
>
> How difficult /would/ it be to fix btrfs, anyway?

Not sure.

Since the file extent backref is not well designed in btrfs, we must 
check the fs tree to determine the correct file offset before splitting 
the fiemap result.

And it may cause extra performance problem.

So I would like to make it as it for now.

Anyway, even btrfs can report correct result, while punching hole at 
range without SHARED flag, it won't free any space...
So the current behavior has its meaning.

Thanks,
Qu

>
> --D
>
>>
>> Test case like generic/372 require explicit reporting will cause false
>> alert on btrfs.
>>
>> Add such runtime check for that requirememt.
>>
>> Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
>> ---
>>  common/reflink    | 44 ++++++++++++++++++++++++++++++++++++++++++++
>>  tests/generic/372 |  1 +
>>  2 files changed, 45 insertions(+)
>>
>> diff --git a/common/reflink b/common/reflink
>> index 8b34046..9ada2e8 100644
>> --- a/common/reflink
>> +++ b/common/reflink
>> @@ -78,6 +78,50 @@ _require_scratch_reflink()
>>  	_scratch_unmount
>>  }
>>
>> +# this test requires scratch fs to report explicit SHARED flag
>> +# e.g.
>> +#   0         4K         8K
>> +#    / File1: Extent 0  \
>> +#   /                    \
>> +#   |<- On disk Extent-->|
>> +#   |        /
>> +#   | File2 /
>> +#     Extent: 0
>> +# Fs supports explicit SHARED extent reporting should report fiemap like:
>> +# File1: 2 extents
>> +# Extent 0-4K: SHARED
>> +# Extent 4-8K:
>> +# File2: 1 extents
>> +# Extent 0-4K: SHARED
>> +#
>> +# Fs doesn't support explicit reporting will report fiemap like:
>> +# File1: 1 extent
>> +# Extent 0-8K: SHARED
>> +# File2: 1 extent
>> +# Extent 0-4K: SHARED
>> +_require_scratch_explicit_shared_extents()
>> +{
>> +	_require_scratch
>> +	_require_fiemap
>> +	_require_scratch_reflink
>> +	_require_xfs_io_command "reflink"
>> +	local nr_extents
>> +
>> +	_scratch_mkfs > /dev/null
>> +	_scratch_mount
>> +
>> +	_pwrite_byte 0x61 0 128k $SCRATCH_MNT/file1
>> +	_reflink_range $SCRATCH_MNT/file1 0 $SCRATCH_MNT/file2 0 64k
>> +
>> +	_scratch_cycle_mount
>> +
>> +	nr_extents=$(_count_extents $SCRATCH_MNT/file1)
>> +	if [ $nr_extents -eq 1 ]; then
>> +		_notrun "Explicit SHARED flag reporting not support by filesystem type: $FSTYP"
>> +	fi
>> +	_scratch_unmount
>> +}
>> +
>>  # this test requires the test fs support dedupe...
>>  _require_test_dedupe()
>>  {
>> diff --git a/tests/generic/372 b/tests/generic/372
>> index 31dff20..51a3eca 100755
>> --- a/tests/generic/372
>> +++ b/tests/generic/372
>> @@ -47,6 +47,7 @@ _supported_os Linux
>>  _supported_fs generic
>>  _require_scratch_reflink
>>  _require_fiemap
>> +_require_scratch_explicit_shared_extents
>>
>>  echo "Format and mount"
>>  _scratch_mkfs > $seqres.full 2>&1
>> --
>> 2.7.4
>>
>>
>>
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