qemu: configurable remote display port boundaries

The defines QEMU_REMOTE_PORT_MIN and QEMU_REMOTE_PORT_MAX were used to
find free port when starting domains. As this was hard-coded to the
same ports as default VNC servers, there were races with these other
programs. This patch includes the possibility to change the default
starting port as well as the maximum port (mostly for completeness) in
qemu config file.

Support for two new config options in qemu.conf is added:
 - remote_port_min (defaults to QEMU_REMOTE_PORT_MIN and
   must be >= than this value)
 - remote_port_max (defaults to QEMU_REMOTE_PORT_MAX and
   must be <= than this value)

src/qemu/libvirtd_qemu.aug

@@ -39,6 +39,9 @@ module Libvirtd_qemu =
                  | str_entry  "spice_tls_x509_cert_dir"
                  | str_entry "spice_password"
 
+   let remote_display_entry = int_entry "remote_display_port_min"
+                 | int_entry "remote_display_port_max"
+
    let security_entry = str_entry "security_driver"
                  | bool_entry "security_default_confined"
                  | bool_entry "security_require_confined"
@@ -72,6 +75,7 @@ module Libvirtd_qemu =
    (* Each enty in the config is one of the following three ... *)
    let entry = vnc_entry
              | spice_entry
+             | remote_display_entry
              | security_entry
              | save_entry
              | process_entry

src/qemu/qemu.conf

@@ -140,6 +140,20 @@
 #spice_password = "XYZ12345"
 
 
+# Override the port for creating both VNC and SPICE sessions (min).
+# This defaults to 5900 and increases for consecutive sessions
+# or when ports are occupied, until it hits the maximum.
+#
+# Minimum must be greater than or equal to 5900 as lower number would
+# result into negative vnc display number.
+#
+# Maximum must be less than 65536, because higher numbers do not make
+# sense as a port number.
+#
+#remote_display_port_min = 5900
+#remote_display_port_max = 65535
+
+
 # The default security driver is SELinux. If SELinux is disabled
 # on the host, then the security driver will automatically disable
 # itself. If you wish to disable QEMU SELinux security driver while

src/qemu/qemu_command.h

@@ -37,6 +37,13 @@
 # define QEMU_VIRTIO_SERIAL_PREFIX "virtio-serial"
 # define QEMU_FSDEV_HOST_PREFIX "fsdev-"
 
+/* These are only defaults, they can be changed now in qemu.conf and
+ * explicitely specified port is checked against these two (makes
+ * sense to limit the values).
+ *
+ * This limitation is mentioned in qemu.conf, so bear in mind that the
+ * configuration file should reflect any changes made to these values.
+ */
 # define QEMU_REMOTE_PORT_MIN  5900
 # define QEMU_REMOTE_PORT_MAX  65535
 

src/qemu/qemu_conf.c

 /*
  * qemu_conf.c: QEMU configuration management
  *
- * Copyright (C) 2006-2011 Red Hat, Inc.
+ * Copyright (C) 2006-2012 Red Hat, Inc.
  * Copyright (C) 2006 Daniel P. Berrange
  *
  * This library is free software; you can redistribute it and/or
@@ -38,6 +38,7 @@
 
 #include "virterror_internal.h"
 #include "qemu_conf.h"
+#include "qemu_command.h"
 #include "qemu_capabilities.h"
 #include "qemu_bridge_filter.h"
 #include "uuid.h"
@@ -89,6 +90,10 @@ int qemudLoadDriverConfig(struct qemud_driver *driver,
         virReportOOMError();
         return -1;
     }
+
+    driver->remotePortMin = QEMU_REMOTE_PORT_MIN;
+    driver->remotePortMax = QEMU_REMOTE_PORT_MAX;
+
     if (!(driver->vncTLSx509certdir = strdup(SYSCONFDIR "/pki/libvirt-vnc"))) {
         virReportOOMError();
         return -1;
@@ -295,6 +300,47 @@ int qemudLoadDriverConfig(struct qemud_driver *driver,
         }
     }
 
+    p = virConfGetValue (conf, "remote_display_port_min");
+    CHECK_TYPE ("remote_display_port_min", VIR_CONF_LONG);
+    if (p) {
+        if (p->l < QEMU_REMOTE_PORT_MIN) {
+            /* if the port is too low, we can't get the display name
+             * to tell to vnc (usually subtract 5900, e.g. localhost:1
+             * for port 5901) */
+            virReportError(VIR_ERR_INTERNAL_ERROR,
+                           _("%s: remote_display_port_min: port must be greater than or equal to %d"),
+                            filename, QEMU_REMOTE_PORT_MIN);
+            virConfFree(conf);
+            return -1;
+        }
+        driver->remotePortMin = p->l;
+    }
+
+    p = virConfGetValue (conf, "remote_display_port_max");
+    CHECK_TYPE ("remote_display_port_max", VIR_CONF_LONG);
+    if (p) {
+        if (p->l > QEMU_REMOTE_PORT_MAX ||
+            p->l < driver->remotePortMin) {
+            virReportError(VIR_ERR_INTERNAL_ERROR,
+                            _("%s: remote_display_port_max: port must be between the minimal port and %d"),
+                            filename, QEMU_REMOTE_PORT_MAX);
+            virConfFree(conf);
+            return -1;
+        }
+        /* increasing the value by 1 makes all the loops going through
+        the bitmap (i = remotePortMin; i < remotePortMax; i++), work as
+        expected. */
+        driver->remotePortMax = p->l + 1;
+    }
+
+    if (driver->remotePortMin > driver->remotePortMax) {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                        _("%s: remote_display_port_min: min port must not be greater than max port"),
+                        filename);
+        virConfFree(conf);
+        return -1;
+    }
+
     p = virConfGetValue (conf, "user");
     CHECK_TYPE ("user", VIR_CONF_STRING);
     if (!(user = strdup(p && p->str ? p->str : QEMU_USER))) {

src/qemu/qemu_conf.h

@@ -95,6 +95,8 @@ struct qemud_driver {
     char *spiceTLSx509certdir;
     char *spiceListen;
     char *spicePassword;
+    int remotePortMin;
+    int remotePortMax;
     char *hugetlbfs_mount;
     char *hugepage_path;
 

src/qemu/qemu_driver.c

@@ -590,11 +590,6 @@ qemudStartup(int privileged) {
     if (!qemu_driver->domainEventState)
         goto error;
 
-    /* Allocate bitmap for vnc port reservation */
-    if ((qemu_driver->reservedRemotePorts =
-         virBitmapAlloc(QEMU_REMOTE_PORT_MAX - QEMU_REMOTE_PORT_MIN)) == NULL)
-        goto out_of_memory;
-
     /* read the host sysinfo */
     if (privileged)
         qemu_driver->hostsysinfo = virSysinfoRead();
@@ -720,6 +715,13 @@ qemudStartup(int privileged) {
     }
     VIR_FREE(driverConf);
 
+    /* Allocate bitmap for remote display port reservations. We cannot
+     * do this before the config is loaded properly, since the port
+     * numbers are configurable now */
+    if ((qemu_driver->reservedRemotePorts =
+         virBitmapAlloc(qemu_driver->remotePortMax - qemu_driver->remotePortMin)) == NULL)
+        goto out_of_memory;
+
     /* We should always at least have the 'nop' manager, so
      * NULLs here are a fatal error
      */

src/qemu/qemu_process.c

@@ -2454,15 +2454,15 @@ static int qemuProcessNextFreePort(struct qemud_driver *driver,
 {
     int i;
 
-    for (i = startPort ; i < QEMU_REMOTE_PORT_MAX; i++) {
+    for (i = startPort ; i < driver->remotePortMax; i++) {
         int fd;
         int reuse = 1;
         struct sockaddr_in addr;
         bool used = false;
 
         if (virBitmapGetBit(driver->reservedRemotePorts,
-                            i - QEMU_REMOTE_PORT_MIN, &used) < 0)
-            VIR_DEBUG("virBitmapGetBit failed on bit %d", i - QEMU_REMOTE_PORT_MIN);
+                            i - driver->remotePortMin, &used) < 0)
+            VIR_DEBUG("virBitmapGetBit failed on bit %d", i - driver->remotePortMin);
 
         if (used)
             continue;
@@ -2484,9 +2484,9 @@ static int qemuProcessNextFreePort(struct qemud_driver *driver,
             VIR_FORCE_CLOSE(fd);
             /* Add port to bitmap of reserved ports */
             if (virBitmapSetBit(driver->reservedRemotePorts,
-                                i - QEMU_REMOTE_PORT_MIN) < 0) {
+                                i - driver->remotePortMin) < 0) {
                 VIR_DEBUG("virBitmapSetBit failed on bit %d",
-                          i - QEMU_REMOTE_PORT_MIN);
+                          i - driver->remotePortMin);
             }
             return i;
         }
@@ -2507,11 +2507,11 @@ static void
 qemuProcessReturnPort(struct qemud_driver *driver,
                       int port)
 {
-    if (port < QEMU_REMOTE_PORT_MIN)
+    if (port < driver->remotePortMin)
         return;
 
     if (virBitmapClearBit(driver->reservedRemotePorts,
-                          port - QEMU_REMOTE_PORT_MIN) < 0)
+                          port - driver->remotePortMin) < 0)
         VIR_DEBUG("Could not mark port %d as unused", port);
 }
 

src/qemu/test_libvirtd_qemu.aug.in

@@ -15,6 +15,8 @@ module Test_libvirtd_qemu =
 { "spice_tls" = "1" }
 { "spice_tls_x509_cert_dir" = "/etc/pki/libvirt-spice" }
 { "spice_password" = "XYZ12345" }
+{ "remote_display_port_min" = "5900" }
+{ "remote_display_port_max" = "65535" }
 { "security_driver" = "selinux" }
 { "security_default_confined" = "1" }
 { "security_require_confined" = "1" }