[Qemu-devel] [PATCH 53/55] nbd/client: Don't hard-disconnect on ESHUTDOWN from server

[Michael Roth <mdroth@linux.vnet.ibm.com>]

From: Eric Blake <eblake@redhat.com>

The NBD spec says that a server may fail any transmission request
with ESHUTDOWN when it is apparent that no further request from
the client can be successfully honored.  The client is supposed
to then initiate a soft shutdown (wait for all remaining in-flight
requests to be answered, then send NBD_CMD_DISC).  However, since
qemu's server never uses ESHUTDOWN errors, this code was mostly
untested since its introduction in commit b6f5d3b5.

More recently, I learned that nbdkit as the NBD server is able to
send ESHUTDOWN errors, so I finally tested this code, and noticed
that our client was special-casing ESHUTDOWN to cause a hard
shutdown (immediate disconnect, with no NBD_CMD_DISC), but only
if the server sends this error as a simple reply.  Further
investigation found that commit d2febedb introduced a regression
where structured replies behave differently than simple replies -
but that the structured reply behavior is more in line with the
spec (even if we still lack code in nbd-client.c to properly quit
sending further requests).  So this patch reverts the portion of
b6f5d3b5 that introduced an improper hard-disconnect special-case
at the lower level, and leaves the future enhancement of a nicer
soft-disconnect at the higher level for another day.

CC: qemu-stable@nongnu.org
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20171113194857.13933-1-eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
(cherry picked from commit 01b05c66a3616d5a4adc39fc90962e9efaf791d1)
 Conflicts:
	nbd/client.c
*drop dep on d2febedb
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
---
 nbd/client.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/nbd/client.c b/nbd/client.c
index 4caff77119..f04e95542f 100644
--- a/nbd/client.c
+++ b/nbd/client.c
@@ -945,12 +945,6 @@ ssize_t nbd_receive_reply(QIOChannel *ioc, NBDReply *reply, Error **errp)
     reply->handle = ldq_be_p(buf + 8);
 
     reply->error = nbd_errno_to_system_errno(reply->error);
-
-    if (reply->error == ESHUTDOWN) {
-        /* This works even on mingw which lacks a native ESHUTDOWN */
-        error_setg(errp, "server shutting down");
-        return -EINVAL;
-    }
     trace_nbd_receive_reply(magic, reply->error, reply->handle);
 
     if (magic != NBD_REPLY_MAGIC) {
-- 
2.11.0