On 8/30/19 6:32 PM, Eric Blake wrote:
>>>> @@ -458,10 +458,13 @@ static int
>>>> nbd_negotiate_handle_export_name(NBDClient *client,
>>>> return -EINVAL;
>>>> }
>>>>
>>>> - trace_nbd_negotiate_new_style_size_flags(client->exp->size,
>>>> - client->exp->nbdflags |
>>>> myflags);
>>>> + myflags = client->exp->nbdflags;
>>>> + if (client->structured_reply) {
>>>> + myflags |= NBD_FLAG_SEND_DF;
>>>> + }
>>>
>>>
>>> why we cant do just
>>> client->exp->nbdflags |= NBD_FLAG_SEND_DF ?
>>
>> Because myflags is the runtime flags for _this_ client, while
>> client->exp->nbdflags are the base flags shared by _all_ clients. If
>> client A requests structured reply, but client B does not, then we don't
>> want to advertise DF to client B; but amending client->exp->nbdflags
>> would have that effect.
>
> I stand corrected - it looks like a fresh client->exp is created per
> client, as evidenced by:
I need to quit replying to myself, but my test was flawed. Modern
clients don't go through NBD_OPT_EXPORT_NAME, so my added line...
> +++ w/nbd/server.c
> @@ -457,6 +457,7 @@ static int
> nbd_negotiate_handle_export_name(NBDClient *client, bool no_zeroes,
> myflags = client->exp->nbdflags;
> if (client->structured_reply) {
> myflags |= NBD_FLAG_SEND_DF;
> + client->exp->nbdflags |= NBD_FLAG_SEND_DF;
> }
...was not getting reached. If I instead tweak NBD_OPT_GO:
diff --git i/nbd/server.c w/nbd/server.c
index 6f3a83704fb3..da1ef793f6df 100644
--- i/nbd/server.c
+++ w/nbd/server.c
@@ -640,6 +640,7 @@ static int nbd_negotiate_handle_info(NBDClient
*client, Error **errp)
myflags = exp->nbdflags;
if (client->structured_reply) {
myflags |= NBD_FLAG_SEND_DF;
+ exp->nbdflags |= NBD_FLAG_SEND_DF;
}
trace_nbd_negotiate_new_style_size_flags(exp->size, myflags);
stq_be_p(buf, exp->size);
> $ ./qemu-nbd -r -f raw file -t &
>
> $ ~/qemu/qemu-io -r -f raw --trace=nbd_\*size_flags
> nbd://localhost:10809 -c quit
> 32145@1567207628.519883:nbd_receive_negotiate_size_flags Size is
> 1049088, export flags 0x48f
>
> $ MY_HACK=1 ~/qemu/qemu-io -r -f raw --trace=nbd_\*size_flags
> nbd://localhost:10809 -c quit
> 32156@1567207630.417815:nbd_receive_negotiate_size_flags Size is
> 1049088, export flags 0x40f
>
Then this reports 0x48f, proving that my initial reaction was correct:
client->exp is a shared resource across multiple connections, but
advertising DF must be a per-connection decision.
> $ ~/qemu/qemu-io -r -f raw --trace=nbd_\*size_flags
> nbd://localhost:10809 -c quit
> 32167@1567207635.202940:nbd_receive_negotiate_size_flags Size is
> 1049088, export flags 0x48f
>
> The export flags change per client, so I _can_ store into
> client->exp->nbdflags. Will do that for v2.
I see nothing to change for v2, so I'm inclined to take this patch as is.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
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