[Libguestfs] [nbdkit PATCH 3/4] truncate: Test for safe multi-connect size handling

[Eric Blake]

On 4/29/19 7:29 AM, Richard W.M. Jones wrote:
> On Sat, Apr 27, 2019 at 04:26:45PM -0500, Eric Blake wrote:
>> Test the just-fixed bug in the truncate filter. Although it is in
>> general unsafe to shrink an image being served by the file plugin, the
>> test is careful to only issue operations on connection A after the
>> file has been resized back to its original length, in order to prove
>> whether the smaller size observed during the short-lived connection B
>> bleeds over into the pread results seen by connection A.  If this test
>> is applied without the previous patch, the second read from A sees all
>> zeroes instead of the desired pattern 2.
>>
>> Signed-off-by: Eric Blake <eblake at redhat.com>

> I guess this test will break in future if we implement and return
> ‘can_resize = true’ in the file plugin?  Or will the (also updated)
> truncate filter be able to cope?

If nothing else, this test will remind us of things to test as we
implement resize support :)

> 
> Anyway since we can adjust or remove the test if necessary later,
> 
> ACK

Thanks for the review; you were right that <pthread.h> is not needed in
patch 2, so with that fix, I'm pushing 1-3. I'll decide if I want to try
a different wording for patch 4, since you were hesitant about the
initial wording attempt.

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

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