[Xen-changelog] [qemu-xen stable-4.10] nbd/client: Don't hard-disconnect on ESHUTDOWN from server

[patchbot@xxxxxxx]

commit b81833fe7d0dd56bec6f4066adec5859af01fdd6
Author:     Eric Blake <eblake@xxxxxxxxxx>
AuthorDate: Mon Nov 13 13:48:57 2017 -0600
Commit:     Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
CommitDate: Wed Dec 6 12:33:46 2017 -0600

    nbd/client: Don't hard-disconnect on ESHUTDOWN from server
    
    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@xxxxxxxxxx
    Signed-off-by: Eric Blake <eblake@xxxxxxxxxx>
    Message-Id: <20171113194857.13933-1-eblake@xxxxxxxxxx>
    Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@xxxxxxxxxxxxx>
    (cherry picked from commit 01b05c66a3616d5a4adc39fc90962e9efaf791d1)
     Conflicts:
        nbd/client.c
    *drop dep on d2febedb
    Signed-off-by: Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
---
 nbd/client.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/nbd/client.c b/nbd/client.c
index 4caff77..f04e955 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) {
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#stable-4.10

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