On 11/09/2017 03:20 AM, Vladimir Sementsov-Ogievskiy wrote: > 09.11.2017 00:57, Eric Blake wrote: >> The NBD spec was recently clarified to state that clients should >> not send 0-length requests to the server, as the server behavior >> is undefined [1]. We know that qemu-nbd's behavior is a successful >> no-op (once it has filtered for read-only exports), but other NBD >> implementations might return an error. To avoid any questionable >> server implementations, it is better to just short-circuit such >> requests on the client side (we are relying on the block layer to >> already filter out requests such as invalid offset, write to a >> read-only volume, and so forth). >> >> [1] https://github.com/NetworkBlockDevice/nbd/commit/ee926037 >> >> Signed-off-by: Eric Blake <ebl...@redhat.com> > > Reviewed-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> >
>> @@ -705,6 +708,9 @@ int nbd_client_co_pwritev(BlockDriverState *bs,
>> uint64_t offset,
>>
>> assert(bytes <= NBD_MAX_BUFFER_SIZE);
>>
>> + if (!bytes) {
>> + return 0;
>> + }
>
> we don't do this check before flags manipulation to do not miss possible
> asserts...
>
>> return nbd_co_request(bs, &request, qiov);
Correct - I put the short-circuit as late as possible to ensure that
preconditions are still being met. I can tweak the commit message to
make that more obvious, if desired.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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