qemu-nbd: Permit --shared=0 for unlimited clients

This gives us better feature parity with QMP nbd-server-start, where
max-connections defaults to 0 for unlimited.

Signed-off-by: Eric Blake <[email protected]>
Message-Id: <[email protected]>
Reviewed-by: Daniel P. Berrangé <[email protected]>

Author: ebblake

docs/tools/qemu-nbd.rst

@@ -136,8 +136,8 @@ driver options if ``--image-opts`` is specified.
 .. option:: -e, --shared=NUM
 
   Allow up to *NUM* clients to share the device (default
-  ``1``). Safe for readers, but for now, consistency is not
-  guaranteed between multiple writers.
+  ``1``), 0 for unlimited. Safe for readers, but for now,
+  consistency is not guaranteed between multiple writers.
 
 .. option:: -t, --persistent
 

qemu-nbd.c

@@ -328,7 +328,7 @@ static void *nbd_client_thread(void *arg)
 
 static int nbd_can_accept(void)
 {
-    return state == RUNNING && nb_fds < shared;
+    return state == RUNNING && (shared == 0 || nb_fds < shared);
 }
 
 static void nbd_update_server_watch(void);
@@ -707,7 +707,7 @@ int main(int argc, char **argv)
             break;
         case 'e':
             if (qemu_strtoi(optarg, NULL, 0, &shared) < 0 ||
-                shared < 1) {
+                shared < 0) {
                 error_report("Invalid shared device number '%s'", optarg);
                 exit(EXIT_FAILURE);
             }
@@ -966,7 +966,7 @@ int main(int argc, char **argv)
     if (socket_activation == 0) {
         int backlog;
 
-        if (persistent) {
+        if (persistent || shared == 0) {
             backlog = SOMAXCONN;
         } else {
             backlog = MIN(shared, SOMAXCONN);