[Qemu-devel] [PATCH 71/97] nbd/client: Send NBD_CMD_DISC if open fails after connect

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

From: Eric Blake <eblake@redhat.com>

If nbd_client_init() fails after we are already connected,
then the server will spam logs with:

Disconnect client, due to: Unexpected end-of-file before all bytes were read

unless we gracefully disconnect before closing the connection.

Ways to trigger this:

$ opts=driver=nbd,export=foo,server.type=inet,server.host=localhost,server.port=10809
$  qemu-img map --output=json --image-opts $opts,read-only=off
$  qemu-img map --output=json --image-opts $opts,x-dirty-bitmap=nosuch:

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20181130023232.3079982-4-eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
(cherry picked from commit c688e6ca7b41a105241054853d250df64addbf8f)
*drop functional dep. on 6c2e581d4d7
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
---
 block/nbd-client.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/block/nbd-client.c b/block/nbd-client.c
index f8c42a6996..1b7b5b0a88 100644
--- a/block/nbd-client.c
+++ b/block/nbd-client.c
@@ -995,13 +995,15 @@ int nbd_client_init(BlockDriverState *bs,
     if (x_dirty_bitmap && !client->info.base_allocation) {
         error_setg(errp, "requested x-dirty-bitmap %s not found",
                    x_dirty_bitmap);
-        return -EINVAL;
+        ret = -EINVAL;
+        goto fail;
     }
     if (client->info.flags & NBD_FLAG_READ_ONLY &&
         !bdrv_is_read_only(bs)) {
         error_setg(errp,
                    "request for write access conflicts with read-only export");
-        return -EACCES;
+        ret = -EACCES;
+        goto fail;
     }
     if (client->info.flags & NBD_FLAG_SEND_FUA) {
         bs->supported_write_flags = BDRV_REQ_FUA;
@@ -1029,4 +1031,17 @@ int nbd_client_init(BlockDriverState *bs,
 
     logout("Established connection with NBD server\n");
     return 0;
+
+ fail:
+    /*
+     * We have connected, but must fail for other reasons. The
+     * connection is still blocking; send NBD_CMD_DISC as a courtesy
+     * to the server.
+     */
+    {
+        NBDRequest request = { .type = NBD_CMD_DISC };
+
+        nbd_send_request(client->ioc ?: QIO_CHANNEL(sioc), &request);
+        return ret;
+    }
 }
-- 
2.17.1