Re: [Qemu-devel] [PATCH] nbd: Don't inf-loop on early EOF

[Eric Blake <eblake@redhat.com>]

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On 11/07/2016 04:22 PM, Max Reitz wrote:
> On 07.11.2016 21:38, Eric Blake wrote:
>> Commit 7d3123e converted a single read_sync() into a while loop
>> that assumed that read_sync() would either make progress or give
>> an error. But when the server hangs up early, the client sees
>> EOF (a read_sync() of 0) and never makes progress, which in turn
>> caused qemu-iotest './check -nbd 83' to go into an infinite loop.
>>
>> Rework the loop to accomodate reads cut short by EOF.
>>
>> Reported-by: Max Reitz <mreitz@redhat.com>
>> Signed-off-by: Eric Blake <eblake@redhat.com>
>> ---
>>  nbd/client.c | 13 +++++++------
>>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> Reviewed-by: Max Reitz <mreitz@redhat.com>
> 
> But what about the server's nbd_negotiate_drop_sync()? It uses pretty
> much the same code, so it seems susceptible to the same issue (only that
> we don't have a test for that side).

If so, that's an older bug (pre-existing back to at least 2.6?), so it
should be a separate fix, if anything.

I guess it's time to figure out how to test the server against
ill-behaved clients...

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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