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Re: [Qemu-trivial] [PATCH for-2.11] nbd/client: Don't hard-disconnect on
From: |
Vladimir Sementsov-Ogievskiy |
Subject: |
Re: [Qemu-trivial] [PATCH for-2.11] nbd/client: Don't hard-disconnect on ESHUTDOWN from server |
Date: |
Thu, 16 Nov 2017 10:33:49 +0300 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 |
13.11.2017 22:48, Eric Blake wrote:
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: address@hidden
Signed-off-by: Eric Blake <address@hidden>
Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>
---
nbd/client.c | 6 ------
1 file changed, 6 deletions(-)
diff --git a/nbd/client.c b/nbd/client.c
index 4e15fc484d..eea236ca06 100644
--- a/nbd/client.c
+++ b/nbd/client.c
@@ -996,15 +996,9 @@ int nbd_receive_reply(QIOChannel *ioc, NBDReply *reply,
Error **errp)
if (ret < 0) {
break;
}
-
trace_nbd_receive_simple_reply(reply->simple.error,
nbd_err_lookup(reply->simple.error),
reply->handle);
- if (reply->simple.error == NBD_ESHUTDOWN) {
- /* This works even on mingw which lacks a native ESHUTDOWN */
- error_setg(errp, "server shutting down");
- return -EINVAL;
- }
break;
case NBD_STRUCTURED_REPLY_MAGIC:
ret = nbd_receive_structured_reply_chunk(ioc, &reply->structured,
errp);
--
Best regards,
Vladimir