Re: [PATCH v2] geceric/362: check truncate can update file size correctly when truncate fails

[Wang Xiaoguang <wangxg.fnst@cn.fujitsu.com>]

hello,

On 07/01/2016 10:55 AM, Eryu Guan wrote:
> On Fri, Jul 01, 2016 at 10:28:28AM +0800, Wang Xiaoguang wrote:
>> hello,
>>
>> On 06/30/2016 09:52 PM, Eryu Guan wrote:
>>> On Thu, Jun 30, 2016 at 04:25:49PM +0800, Wang Xiaoguang wrote:
>>>> In btrfs, when truncate operation fails for enospc reason, file may still
>>>> have some disk blocks, but it will fail to update filesize accordingly.
>>>>
>>>> Kernel commit c0d2f61 has fixed this bug for btrfs:
>>>>       btrfs: fix disk_i_size update bug when ftruncate() fails
>>>>
>>>> Signed-off-by: Wang Xiaoguang <wangxg.fnst@cn.fujitsu.com>
>>>> ---
>>>> v2: move this test to generic test and add comments why testcase
>>>> use reflink.
>>> Thanks for the updated version. Did it fail for you when testing on
>>> unpatched kernel? I ran the test more than 10 times on 4.6 kernel (which
>>> doesn't have the fix) and all passed, as well as RHEL7 kernel.
>>>
>>> Can you please confirm?
>> I tested this case in v4.6-rc7-162-g415b35a and it failed as expected,
>> but I used the newest version btrfs-progs.
>> In RHEL7.2ga, its btrfs-progs version is btrfs-progs-3.19.1-1.el7.x86_64,
>> which is somewhat old. For small fs, it'll enable mixed mode for data and
>> metadata default, so the reflink operation in this test case does not
>> consume
>> enough metadata, truncate operation can still succeed, then test will always
>> pass. I can create a big fs to have test, but then this fs will have more
>> metadata, which then need more reflink operations to consume metadata and
>> increase the test time greatly.
>>
>> In mkfs.btrfs manpage, there is such description：
>>       versions up to 4.2.x forced the mixed mode for devices smaller
>>       than 1GiB. This has been removed in 4.3+ as it caused some
>>       usability issues.
> I also tested on 4.6 kernel with v4.6 btrfs-progs, it passed 10+ times
> without a fail. I was testing on a 4vcpu kvm guest with 8G memory,
> TEST_DEV and SCRATCH_DEV are all 15G in size, not sure if that matters.
Sorry, I run this test case in v4.6, it still failed.
Would you please give me your kernel version and btrfs-progs version,
like this format: v4.6-rc7-162-g415b35a, which is generated by "describe",
then I can do some further investigation, thanks.

Regards,
Xiaoguang Wang
>
> Thanks,
> Eryu
>
>