nbd/client: Fix error messages during NBD_INFO_BLOCK_SIZE

A missing space makes for poor error messages, and sizes can't
go negative.  Also, we missed diagnosing a server that sends
a maximum block size less than the minimum.

Fixes: 081dd1fe
CC: qemu-stable@nongnu.org
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20180501154654.943782-1-eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

nbd/client.c

@@ -435,8 +435,8 @@ static int nbd_opt_go(QIOChannel *ioc, const char *wantname,
             }
             be32_to_cpus(&info->min_block);
             if (!is_power_of_2(info->min_block)) {
-                error_setg(errp, "server minimum block size %" PRId32
-                           "is not a power of two", info->min_block);
+                error_setg(errp, "server minimum block size %" PRIu32
+                           " is not a power of two", info->min_block);
                 nbd_send_opt_abort(ioc);
                 return -1;
             }
@@ -450,8 +450,8 @@ static int nbd_opt_go(QIOChannel *ioc, const char *wantname,
             be32_to_cpus(&info->opt_block);
             if (!is_power_of_2(info->opt_block) ||
                 info->opt_block < info->min_block) {
-                error_setg(errp, "server preferred block size %" PRId32
-                           "is not valid", info->opt_block);
+                error_setg(errp, "server preferred block size %" PRIu32
+                           " is not valid", info->opt_block);
                 nbd_send_opt_abort(ioc);
                 return -1;
             }
@@ -462,6 +462,12 @@ static int nbd_opt_go(QIOChannel *ioc, const char *wantname,
                 return -1;
             }
             be32_to_cpus(&info->max_block);
+            if (info->max_block < info->min_block) {
+                error_setg(errp, "server maximum block size %" PRIu32
+                           " is not valid", info->max_block);
+                nbd_send_opt_abort(ioc);
+                return -1;
+            }
             trace_nbd_opt_go_info_block_size(info->min_block, info->opt_block,
                                              info->max_block);
             break;