On 8/30/19 1:07 PM, Vladimir Sementsov-Ogievskiy wrote:
> 23.08.2019 17:37, Eric Blake wrote:
>> Commit fe0480d6 and friends added BDRV_REQ_NO_FALLBACK as a way to
>> avoid wasting time on a preliminary write-zero request that will later
>> be rewritten by actual data, if it is known that the write-zero
>> request will use a slow fallback; but in doing so, could not optimize
>> for NBD.  The NBD specification is now considering an extension that
>> will allow passing on those semantics; this patch updates the new
>> protocol bits and 'qemu-nbd --list' output to recognize the bit, as
>> well as the new errno value possible when using the new flag; while
>> upcoming patches will improve the client to use the feature when
>> present, and the server to advertise support for it.
>>

>> +++ b/nbd/server.c
>> @@ -55,6 +55,8 @@ static int system_errno_to_nbd_errno(int err)
>>           return NBD_ENOSPC;
>>       case EOVERFLOW:
>>           return NBD_EOVERFLOW;
>> +    case ENOTSUP:
>> +        return NBD_ENOTSUP;
> 

I'm squashing this in:

diff --git i/nbd/server.c w/nbd/server.c
index b3bd08ef2953..4992148de1c4 100644
--- i/nbd/server.c
+++ w/nbd/server.c
@@ -56,6 +56,9 @@ static int system_errno_to_nbd_errno(int err)
     case EOVERFLOW:
         return NBD_EOVERFLOW;
     case ENOTSUP:
+#if ENOTSUP != EOPNOTSUPP
+    case EOPNOTSUPP:
+#endif
         return NBD_ENOTSUP;
     case ESHUTDOWN:
         return NBD_ESHUTDOWN;

It makes no difference on Linux, but may matter on other platforms
(since POSIX says the two may be equivalent, but may also be distinct).

> 

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