[PATCH v2 for 8.0?] nbd/server: Request TCP_NODELAY

[Eric Blake <eblake@redhat.com>]

Nagle's algorithm adds latency in order to reduce network packet
overhead on small packets.  But when we are already using corking to
merge smaller packets into transactional requests, the extra delay
from TCP defaults just gets in the way (see recent commit bd2cd4a4).

For reference, qemu as an NBD client already requests TCP_NODELAY (see
nbd_connect() in nbd/client-connection.c); as does libnbd as a client
[1], and nbdkit as a server [2].  Furthermore, the NBD spec recommends
the use of TCP_NODELAY [3].

[1] https://gitlab.com/nbdkit/libnbd/-/blob/a48a1142/generator/states-connect.c#L39
[2] https://gitlab.com/nbdkit/nbdkit/-/blob/45b72f5b/server/sockets.c#L430
[3] https://github.com/NetworkBlockDevice/nbd/blob/master/doc/proto.md#protocol-phases

CC: Florian Westphal <fw@strlen.de>
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20230327192947.1324372-1-eblake@redhat.com>
---

v2 fix typo, enhance commit message

Given that corking made it in through Kevin's tree for 8.0-rc2 but
this one did not, but I didn't get any R-b, is there any objection to
me doing a pull request to get this into 8.0-rc3?

 nbd/server.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/nbd/server.c b/nbd/server.c
index 848836d4140..3d8d0d81df2 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -2758,6 +2758,7 @@ void nbd_client_new(QIOChannelSocket *sioc,
     }
     client->tlsauthz = g_strdup(tlsauthz);
     client->sioc = sioc;
+    qio_channel_set_delay(QIO_CHANNEL(sioc), false);
     object_ref(OBJECT(client->sioc));
     client->ioc = QIO_CHANNEL(sioc);
     object_ref(OBJECT(client->ioc));

base-commit: efcd0ec14b0fe9ee0ee70277763b2d538d19238d
-- 
2.39.2