Re: [PATCH] xfs/194: fix the exception when run on 4k sector drives

[Zirong Lang <zlang@redhat.com>]

----- 原始邮件 -----
> 发件人: "Eric Sandeen" <sandeen@sandeen.net>
> 收件人: "Dave Chinner" <david@fromorbit.com>, "Eric Sandeen" <sandeen@redhat.com>
> 抄送: "Zorro Lang" <zlang@redhat.com>, fstests@vger.kernel.org
> 发送时间: 星期三, 2015年 8 月 19日 上午 7:03:45
> 主题: Re: [PATCH] xfs/194: fix the exception when run on 4k sector drives
> 
> On 8/18/15 5:43 PM, Dave Chinner wrote:
> > On Tue, Aug 18, 2015 at 05:33:05PM -0500, Eric Sandeen wrote:
> >> On 8/18/15 5:28 PM, Dave Chinner wrote:
> >>> On Wed, Aug 19, 2015 at 01:21:51AM +0800, Zorro Lang wrote:
> >>>> @@ -50,6 +50,16 @@ rm -f $seqres.full
> >>>>  # For this test we use block size = 1/8 page size
> >>>>  pgsize=`$here/src/feature -s`
> >>>>  blksize=`expr $pgsize / 8`
> >>>> +secsize=`_min_dio_alignment $SCRATCH_DEV`
> >>>> +
> >>>> +# The minimal blksize can't less than sector size, So if
> >>>> +# blksize < secsize, we should adjust blksize and pgsize number.
> >>>> +# Of course, if we adjust pgsize, pgsize won't equal to the
> >>>> +# real page size of system.
> >>>> +if [ $blksize -lt $secsize ];then
> >>>> +        blksize=$secsize
> >>>> +        pgsize=`expr $blksize \* 8`
> >>>> +fi
> >>>
> >>> No, this is wrong. the page size stays fixed at the machine page
> >>> size. We are testing *sub-page block sizes* here and the sector size
> >>> must be <= page size. Increasing the "page size" to larger than the
> >>> machine page size does not make the kernel use larger page sizes.
> >>>
> >>> IOWs, if you've got sector size = page size (e.g. 4k sector device)
> >>> then no matter what you say $pgsize is, the kernel will see a block
> >>> size = page size test.

Yes, I know I can't change page size. So I said "for sure the consistency
of test result, I repair pgsize(already not real page size) number according
to the new blksize." in git commit message.

Eric said in xfs/194 "Test mapping around/over holes for sub-page blocks",
If the sector size = page size, I have no idea how to make sub-page blocks.
So in this situation, I set pgsize=`expr $blksize \* 8` just for the test
output suit for 194.out.

Or we don't care pgsize, just set blksize=`_min_dio_alignment $SCRATCH_DEV`,
and then replace all $pgsize to `expr $blksize \* 8`. If page size > blksize,
that's good. If not, we can't do more things about that, so just make it run pass.

> >>>
> >>> This whole chunk of code can simply be replaced with:
> >>>
> >>> blksize=`_min_dio_alignment $SCRATCH_DEV`
> >>>
> >>> Because that's what we actually need to test...
> >>
> >> That won't work either, because we could easily get 512 from that.
> > 
> > If 'blockdev --getss $dev' returns 512, then the device supports 512
> > byte IOs and so it is fine to do 512 byte IOs in the test.
> > 
> >> and then this test:
> >>
> >> # Now try the same thing but write a sector in the middle of that hole
> >> # If things go badly stale data will be exposed either side.
> >> # This is most interesting for block size > 512 (page size > 4096)
> >>
> >> # We *should* get:
> >> # |1100|HHHH|33HH|HHHH|2222|----|----|----|
> >>
> >> echo "== Test 4 =="
> >> xfs_io \
> >> -c "pwrite -S 0x11 -b $pgsize 0 $pgsize" \
> >> -c "mmap -r 0 $blksize" -c "mread 0 $blksize" -c "munmap" \
> >> -c "truncate `expr $blksize / 2`" \
> >> -c "truncate `expr $blksize + 1`" \
> >> -c "pwrite -S 0x22 -b $blksize `expr $pgsize / 2` $blksize" \
> >> -c "pwrite -S 0x33 -b 512 `expr $blksize \* 2` 512" \
> >> -t -d -f $SCRATCH_MNT/testfile4 >> $seqres.full
> >>
> >> will be impossible.
> >>
> >> AFAICT everything works except for that explicit 512-byte IO.
> > 
> > Right. That hard coded 512 needs to change to $blksize, because
> > blksize is now equal to the sector size. I thought this would be
> > obvious to the reader, so I didn't comment on it.
> 
> if that last IO is $blksize, and blocksize == sector size, then the
> test won't be testing what it's designed to test here, i.e. a
> sub-block direct IO write.

What do you think about loop device? If page size(4k) = sector size(4k), how
about use loop device? I think it will be 512 sector size as default?

Thanks,
Zorro

> 
> # We *should* get:
> # |1100|HHHH|33HH|HHHH|2222|----|----|----|
>              ^^
>              this
> 
> -Eric
> 
>