nbd-client: fix handling of hungup connections

After the switch to reading replies in a coroutine, nothing is
reentering pending receive coroutines if the connection hangs.
Move nbd_recv_coroutines_enter_all to the reply read coroutine,
which is the place where hangups are detected.  nbd_teardown_connection
can simply wait for the reply read coroutine to detect the hangup
and clean up after itself.

This wouldn't be enough though because nbd_receive_reply returns 0
(rather than -EPIPE or similar) when reading from a hung connection.
Fix the return value check in nbd_read_reply_entry.

This fixes qemu-iotests 083.

Reported-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20170314111157.14464-1-pbonzini@redhat.com
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

block/nbd-client.c

@@ -33,17 +33,15 @@
 #define HANDLE_TO_INDEX(bs, handle) ((handle) ^ ((uint64_t)(intptr_t)bs))
 #define INDEX_TO_HANDLE(bs, index)  ((index)  ^ ((uint64_t)(intptr_t)bs))
 
-static void nbd_recv_coroutines_enter_all(BlockDriverState *bs)
+static void nbd_recv_coroutines_enter_all(NBDClientSession *s)
 {
-    NBDClientSession *s = nbd_get_client_session(bs);
     int i;
 
     for (i = 0; i < MAX_NBD_REQUESTS; i++) {
         if (s->recv_coroutine[i]) {
-            qemu_coroutine_enter(s->recv_coroutine[i]);
+            aio_co_wake(s->recv_coroutine[i]);
         }
     }
-    BDRV_POLL_WHILE(bs, s->read_reply_co);
 }
 
 static void nbd_teardown_connection(BlockDriverState *bs)
@@ -58,7 +56,7 @@ static void nbd_teardown_connection(BlockDriverState *bs)
     qio_channel_shutdown(client->ioc,
                          QIO_CHANNEL_SHUTDOWN_BOTH,
                          NULL);
-    nbd_recv_coroutines_enter_all(bs);
+    BDRV_POLL_WHILE(bs, client->read_reply_co);
 
     nbd_client_detach_aio_context(bs);
     object_unref(OBJECT(client->sioc));
@@ -76,7 +74,7 @@ static coroutine_fn void nbd_read_reply_entry(void *opaque)
     for (;;) {
         assert(s->reply.handle == 0);
         ret = nbd_receive_reply(s->ioc, &s->reply);
-        if (ret < 0) {
+        if (ret <= 0) {
             break;
         }
 
@@ -103,6 +101,8 @@ static coroutine_fn void nbd_read_reply_entry(void *opaque)
         aio_co_wake(s->recv_coroutine[i]);
         qemu_coroutine_yield();
     }
+
+    nbd_recv_coroutines_enter_all(s);
     s->read_reply_co = NULL;
 }
 

nbd/client.c

@@ -812,6 +812,6 @@ ssize_t nbd_receive_reply(QIOChannel *ioc, NBDReply *reply)
         LOG("invalid magic (got 0x%" PRIx32 ")", magic);
         return -EINVAL;
     }
-    return 0;
+    return sizeof(buf);
 }