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Re: [Qemu-block] Failing QEMU iotest 175

From: Eric Blake
Subject: Re: [Qemu-block] Failing QEMU iotest 175
Date: Fri, 3 May 2019 15:21:06 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1

On 5/2/19 11:37 PM, Thomas Huth wrote:
> On 02/05/2019 23.56, Eric Blake wrote:
>> On 4/28/19 10:18 AM, Thomas Huth wrote:
>>> QEMU iotest 175 is failing for me when I run it with -raw:
>>>  == creating image with default preallocation ==
>>>  Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576
>>> -size=1048576, blocks=0
>>> +size=1048576, blocks=2
>> What filesystem?
> ext4

Hmm, it's passing for me on ext4, but that probably means we have
different configuration parameters. I'm not sure how to easily show what
parameters a particular ext4 partition uses to compare the differences
between your setup and mine (mine is tuned to whatever defaults Fedora's
installer chose on my behalf), so maybe someone else can chime in.

>> It should be fairly obvious that 'stat -c blocks=%b' is
>> file-system dependent (some allocate slightly more or less space, based
>> on granularities and on predictions of future use), so we may need to
>> update the test to apply a filter or otherwise allow a bit of fuzz in
>> the answer. But 0/2 is definitely different than...
>>>  == creating image with preallocation off ==
>>>  Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 preallocation=off
>>> -size=1048576, blocks=0
>>> +size=1048576, blocks=2
>>>  == creating image with preallocation full ==
>>>  Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 preallocation=full
>>> -size=1048576, blocks=2048
>>> +size=1048576, blocks=2050
>> 2048/2050, so we DO have some indication of whether the file is sparse
>> or fully allocated.
> Maybe we could check that the value after "blocks=" is a single digit in
> the first case, and matches "blocks=20.." in the second case?

I wonder if 'qemu-img map --output=json $TEST_IMG' might be any more
reliable (at least for ignoring any extra block allocations associated
with the file, if it is some journaling option or xattr or other reason
why your files seem to occupy more disk sectors than just the size of
the file would imply).

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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