Add support for file descriptor sets by converting some of the 
command line parameters to use /dev/fdset/%d if -add-fd is found
to be supported by QEMU. For those devices libvirt now open()s
the device to obtain the file descriptor and 'transfers' the 
fd using virCommand.

For the following fragments of domain XML


    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file='/var/lib/libvirt/images/fc14-x86_64.img'/>
      <target dev='hda' bus='ide'/>
      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
    </disk>

   <serial type='dev'>
      <source path='/dev/ttyS0'/>
      <target port='0'/>
    </serial>
    <serial type='pipe'>
      <source path='/tmp/testpipe'/>
      <target port='1'/>
    </serial>

libvirt now creates the following parts for the QEMU command line:

old: -drive file=/var/lib/libvirt/images/fc14-x86_64.img,if=none,id=drive-ide0-0-0,format=raw
new: -add-fd set=1,fd=23,opaque=RDONLY:/var/lib/libvirt/images/fc14-x86_64.img
     -add-fd set=1,fd=24,opaque=RDWR:/var/lib/libvirt/images/fc14-x86_64.img
     -drive file=/dev/fdset/1,if=none,id=drive-ide0-0-0,format=raw

old: -chardev tty,id=charserial0,path=/dev/ttyS0
new: -add-fd set=1,fd=30,opaque=/dev/ttyS0
     -chardev tty,id=charserial0,path=/dev/fdset/1

old: -chardev pipe,id=charserial1,path=/tmp/testpipe
new: -add-fd set=2,fd=32,opaque=/tmp/testpipe
     -chardev pipe,id=charserial1,path=/dev/fdset/2

Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>

---

v1->v2:
   - Addressed many of Eric's comment; many changes, though
   - virBitmap holds used file descriptor sets; it's attached to
     QEMU private domain structure
   - persisting and parsing the fdset in the virDomainDeviceInfo XML
   - rebuilding the fdset bitmap upon libvirt start and after parsing
     the virDomainDeviceInfo XML

---
 src/conf/capabilities.h  |    5 
 src/conf/domain_conf.c   |   20 +++
 src/conf/domain_conf.h   |    1 
 src/lxc/lxc_domain.c     |    3 
 src/qemu/qemu_command.c  |  239 ++++++++++++++++++++++++++++++++++++++---------
 src/qemu/qemu_command.h  |   15 ++
 src/qemu/qemu_domain.c   |   26 ++++-
 src/qemu/qemu_driver.c   |    5 
 src/qemu/qemu_driver.h   |    4 
 src/qemu/qemu_hotplug.c  |    9 +
 src/qemu/qemu_process.c  |    3 
 tests/qemuxml2argvtest.c |    4 
 tests/qemuxmlnstest.c    |    9 +
 13 files changed, 281 insertions(+), 62 deletions(-)

Index: libvirt/src/qemu/qemu_command.c
===================================================================
--- libvirt.orig/src/qemu/qemu_command.c
+++ libvirt/src/qemu/qemu_command.c
@@ -46,6 +46,7 @@
 #include "base64.h"
 #include "device_conf.h"
 #include "virstoragefile.h"
+#include "qemu_driver.h"
 
 #include <sys/stat.h>
 #include <fcntl.h>
@@ -133,6 +134,70 @@ VIR_ENUM_IMPL(qemuDomainFSDriver, VIR_DO
 
 
 /**
+ * qemuCommandPrintFDSet:
+ * @fdset: the number of the file descriptor set to which @fd belongs
+ * @fd: fd that will be assigned to QEMU
+ * @open_flags: the flags used for opening the fd; of interest are only
+ *               O_RDONLY, O_WRONLY, O_RDWR
+ * @name: optional name of the file
+ *
+ * Write the parameters for the QEMU -add-fd command line option
+ * for the given file descriptor and return the string.
+ * This function for example returns "set=10,fd=20,opaque=RDWR:/foo/bar".
+ */
+static char *
+qemuCommandPrintFDSet(int fdset, int fd, int open_flags, const char *name)
+{
+    const char *mode = "";
+    virBuffer buf = VIR_BUFFER_INITIALIZER;
+
+    if (name) {
+        switch ((open_flags & O_ACCMODE)) {
+        case O_RDONLY:
+            mode = "RDONLY:";
+            break;
+        case O_WRONLY:
+            mode = "WRONLY:";
+            break;
+        case O_RDWR:
+            mode = "RDWR:";
+            break;
+        }
+    }
+
+    virBufferAsprintf(&buf, "set=%d,fd=%d%s%s", fdset, fd,
+                      (name) ? ",opaque=" : "",
+                      mode);
+    if (name)
+        virBufferEscape(&buf, ',', ",", "%s", name);
+
+    if (virBufferError(&buf)) {
+        virReportOOMError();
+        virBufferFreeAndReset(&buf);
+        return NULL;
+    }
+
+    return virBufferContentAndReset(&buf);
+}
+
+/**
+ * qemuCommandPrintDevSet:
+ * @buf: buffer to write the file descriptor set string
+ * @fdset: the file descriptor set
+ *
+ * Get the parameters for the QEMU path= parameter where a file
+ * descriptor is accessed via a file descriptor set, for example
+ * /dev/fdset/10. The file descriptor must previously have been
+ * 'transferred' in a virCommandTransfer() call.
+ */
+static void
+qemuCommandPrintDevSet(virBufferPtr buf, int fdset)
+{
+    virBufferAsprintf(buf, "/dev/fdset/%d", fdset);
+}
+
+
+/**
  * qemuPhysIfaceConnect:
  * @def: the definition of the VM (needed by 802.1Qbh and audit)
  * @driver: pointer to the driver instance
@@ -2223,11 +2288,72 @@ no_memory:
     goto cleanup;
 }
 
+static void
+qemuCreatePathForFilePath(virQEMUDriverPtr driver, virBufferPtr buf,
+                          const char *prefix, const char *path,
+                          const int *open_flags,
+                          virCommandPtr cmd, virBitmapPtr fdset,
+                          unsigned int *fdsetnum,
+                          qemuCapsPtr caps)
+{
+    char *fdsetstr = NULL;
+    int i;
+
+    virBufferAdd(buf, prefix, -1);
+    /*
+     * cmd == NULL hints at hotplugging; use old way of doing things
+     * fdset == NULL hints at a call path where we should not open files
+     *               In this case we fall back to the old command line
+     *               (at least for now)
+     */
+    if (!cmd || !fdset || !qemuCapsGet(caps, QEMU_CAPS_ADD_FD)) {
+        virBufferEscape(buf, ',', ",", "%s", path);
+    } else {
+        ssize_t nextfdset;
+
+        nextfdset = virBitmapSetNextBit(fdset, 0);
+        if (nextfdset < 0) {
+            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                           _("File descriptor set is full"));
+            goto error;
+        }
+        *fdsetnum = nextfdset;
+
+        qemuCommandPrintDevSet(buf, *fdsetnum);
+
+        i = 0;
+        while (open_flags[i] != -1) {
+            int fd = qemuOpenFile(driver, path, open_flags[i], NULL, NULL);
+            if (fd < 0) {
+                virReportError(VIR_ERR_INTERNAL_ERROR,
+                               _("Could not open %s"), path);
+                goto error;
+            }
+            virCommandTransferFD(cmd, fd);
+
+            fdsetstr = qemuCommandPrintFDSet(*fdsetnum, fd, open_flags[i],
+                                             path);
+            if (!fdsetstr)
+                goto error;
+            virCommandAddArgList(cmd, "-add-fd", fdsetstr, NULL);
+            VIR_FREE(fdsetstr);
+
+            i++;
+        }
+    }
+
+error:
+    return;
+}
+
 char *
 qemuBuildDriveStr(virConnectPtr conn ATTRIBUTE_UNUSED,
                   virDomainDiskDefPtr disk,
                   bool bootable,
-                  qemuCapsPtr caps)
+                  qemuCapsPtr caps,
+                  virCommandPtr cmd,
+                  virQEMUDriverPtr driver,
+                  virBitmapPtr fdset)
 {
     virBuffer opt = VIR_BUFFER_INITIALIZER;
     const char *bus = virDomainDiskQEMUBusTypeToString(disk->bus);
@@ -2389,7 +2515,12 @@ qemuBuildDriveStr(virConnectPtr conn ATT
                                  "block type disk"));
                 goto error;
             }
-            virBufferEscape(&opt, ',', ",", "file=%s,", disk->src);
+            qemuCreatePathForFilePath(driver, &opt,
+                                      "file=", disk->src,
+                                      (int[]){O_RDONLY, O_RDWR, -1},
+                                      cmd, fdset, &disk->info.fdset,
+                                      caps);
+            virBufferAddChar(&opt, ',');
         }
     }
     if (qemuCapsGet(caps, QEMU_CAPS_DEVICE))
@@ -2886,7 +3017,10 @@ error:
 
 
 char *qemuBuildFSStr(virDomainFSDefPtr fs,
-                     qemuCapsPtr caps ATTRIBUTE_UNUSED)
+                     qemuCapsPtr caps ATTRIBUTE_UNUSED,
+                     virCommandPtr cmd,
+                     virQEMUDriverPtr qemu_driver,
+                     virBitmapPtr fdset)
 {
     virBuffer opt = VIR_BUFFER_INITIALIZER;
     const char *driver = qemuDomainFSDriverTypeToString(fs->fsdriver);
@@ -2935,7 +3069,9 @@ char *qemuBuildFSStr(virDomainFSDefPtr f
     }
 
     virBufferAsprintf(&opt, ",id=%s%s", QEMU_FSDEV_HOST_PREFIX, fs->info.alias);
-    virBufferAsprintf(&opt, ",path=%s", fs->src);
+    qemuCreatePathForFilePath(qemu_driver, &opt,
+                              ",path=", fs->src, (int[]){O_RDWR, -1},
+                              cmd, fdset, &fs->info.fdset, caps);
 
     if (fs->readonly) {
         if (qemuCapsGet(caps, QEMU_CAPS_FSDEV_READONLY)) {
@@ -3884,12 +4020,13 @@ qemuBuildUSBHostdevUsbDevStr(virDomainHo
 }
 
 
-
 /* This function outputs a -chardev command line option which describes only the
  * host side of the character device */
 static char *
 qemuBuildChrChardevStr(virDomainChrSourceDefPtr dev, const char *alias,
-                       qemuCapsPtr caps)
+                       qemuCapsPtr caps, virCommandPtr cmd,
+                       virQEMUDriverPtr driver,
+                       virBitmapPtr fdset, unsigned int *fdsetnum)
 {
     virBuffer buf = VIR_BUFFER_INITIALIZER;
     bool telnet;
@@ -3908,19 +4045,29 @@ qemuBuildChrChardevStr(virDomainChrSourc
         break;
 
     case VIR_DOMAIN_CHR_TYPE_DEV:
-        virBufferAsprintf(&buf, "%s,id=char%s,path=%s",
+        virBufferAsprintf(&buf, "%s,id=char%s",
                           STRPREFIX(alias, "parallel") ? "parport" : "tty",
-                          alias, dev->data.file.path);
+                          alias);
+        qemuCreatePathForFilePath(driver, &buf,
+                                  ",path=", dev->data.file.path,
+                                   (int[]){O_RDWR, -1}, cmd, fdset,
+                                   fdsetnum, caps);
         break;
 
     case VIR_DOMAIN_CHR_TYPE_FILE:
-        virBufferAsprintf(&buf, "file,id=char%s,path=%s", alias,
-                          dev->data.file.path);
+        virBufferAsprintf(&buf, "file,id=char%s", alias);
+        qemuCreatePathForFilePath(driver, &buf,
+                                  ",path=", dev->data.file.path,
+                                  (int[]){O_RDWR, -1}, cmd, fdset, fdsetnum,
+                                  caps);
         break;
 
     case VIR_DOMAIN_CHR_TYPE_PIPE:
-        virBufferAsprintf(&buf, "pipe,id=char%s,path=%s", alias,
-                          dev->data.file.path);
+        virBufferAsprintf(&buf, "pipe,id=char%s",alias);
+        qemuCreatePathForFilePath(driver, &buf,
+                                  ",path=", dev->data.file.path,
+                                  (int[]){O_RDWR, -1}, cmd, fdset, fdsetnum,
+                                  caps);
         break;
 
     case VIR_DOMAIN_CHR_TYPE_STDIO:
@@ -5056,7 +5203,8 @@ qemuBuildCommandLine(virConnectPtr conn,
                      const char *migrateFrom,
                      int migrateFd,
                      virDomainSnapshotObjPtr snapshot,
-                     enum virNetDevVPortProfileOp vmop)
+                     enum virNetDevVPortProfileOp vmop,
+                     virBitmapPtr fdset)
 {
     int i, j;
     int disableKQEMU = 0;
@@ -5350,11 +5498,11 @@ qemuBuildCommandLine(virConnectPtr conn,
         /* Use -chardev if it's available */
         if (qemuCapsGet(caps, QEMU_CAPS_CHARDEV)) {
 
-            virCommandAddArg(cmd, "-chardev");
             if (!(chrdev = qemuBuildChrChardevStr(monitor_chr, "monitor",
-                                                  caps)))
+                                                  caps, cmd, driver, fdset,
+                                                  NULL)))
                 goto error;
-            virCommandAddArg(cmd, chrdev);
+            virCommandAddArgList(cmd, "-chardev", chrdev, NULL);
             VIR_FREE(chrdev);
 
             virCommandAddArg(cmd, "-mon");
@@ -5797,8 +5945,6 @@ qemuBuildCommandLine(virConnectPtr conn,
                 break;
             }
 
-            virCommandAddArg(cmd, "-drive");
-
             /* Unfortunately it is not possible to use
                -device for floppies, or Xen paravirt
                devices. Fortunately, those don't need
@@ -5814,12 +5960,12 @@ qemuBuildCommandLine(virConnectPtr conn,
             }
             optstr = qemuBuildDriveStr(conn, disk,
                                        emitBootindex ? false : !!bootindex,
-                                       caps);
+                                       caps, cmd, driver, fdset);
             if (deviceFlagMasked)
                 qemuCapsSet(caps, QEMU_CAPS_DEVICE);
             if (!optstr)
                 goto error;
-            virCommandAddArg(cmd, optstr);
+            virCommandAddArgList(cmd, "-drive", optstr, NULL);
             VIR_FREE(optstr);
 
             if (!emitBootindex)
@@ -5995,7 +6141,7 @@ qemuBuildCommandLine(virConnectPtr conn,
             virDomainFSDefPtr fs = def->fss[i];
 
             virCommandAddArg(cmd, "-fsdev");
-            if (!(optstr = qemuBuildFSStr(fs, caps)))
+            if (!(optstr = qemuBuildFSStr(fs, caps, cmd, driver, fdset)))
                 goto error;
             virCommandAddArg(cmd, optstr);
             VIR_FREE(optstr);
@@ -6275,14 +6421,14 @@ qemuBuildCommandLine(virConnectPtr conn,
                 goto error;
             }
 
-            virCommandAddArg(cmd, "-chardev");
             if (!(devstr = qemuBuildChrChardevStr(&smartcard->data.passthru,
                                                   smartcard->info.alias,
-                                                  caps))) {
+                                                  caps, cmd, driver, fdset,
+                                                  &smartcard->info.fdset))) {
                 virBufferFreeAndReset(&opt);
                 goto error;
             }
-            virCommandAddArg(cmd, devstr);
+            virCommandAddArgList(cmd, "-chardev", devstr, NULL);
             VIR_FREE(devstr);
 
             virBufferAsprintf(&opt, "ccid-card-passthru,chardev=char%s",
@@ -6313,12 +6459,13 @@ qemuBuildCommandLine(virConnectPtr conn,
             /* Use -chardev with -device if they are available */
             if (qemuCapsGet(caps, QEMU_CAPS_CHARDEV) &&
                 qemuCapsGet(caps, QEMU_CAPS_DEVICE)) {
-                virCommandAddArg(cmd, "-chardev");
                 if (!(devstr = qemuBuildChrChardevStr(&serial->source,
                                                       serial->info.alias,
-                                                      caps)))
+                                                      caps, cmd, driver,
+                                                      fdset,
+                                                      &serial->info.fdset)))
                     goto error;
-                virCommandAddArg(cmd, devstr);
+                virCommandAddArgList(cmd, "-chardev", devstr, NULL);
                 VIR_FREE(devstr);
 
                 virCommandAddArg(cmd, "-device");
@@ -6350,12 +6497,13 @@ qemuBuildCommandLine(virConnectPtr conn,
             /* Use -chardev with -device if they are available */
             if (qemuCapsGet(caps, QEMU_CAPS_CHARDEV) &&
                 qemuCapsGet(caps, QEMU_CAPS_DEVICE)) {
-                virCommandAddArg(cmd, "-chardev");
                 if (!(devstr = qemuBuildChrChardevStr(&parallel->source,
                                                       parallel->info.alias,
-                                                      caps)))
+                                                      caps, cmd, driver,
+                                                      fdset,
+                                                      &parallel->info.fdset)))
                     goto error;
-                virCommandAddArg(cmd, devstr);
+                virCommandAddArgList(cmd, "-chardev", devstr, NULL);
                 VIR_FREE(devstr);
 
                 virCommandAddArg(cmd, "-device");
@@ -6387,12 +6535,12 @@ qemuBuildCommandLine(virConnectPtr conn,
                 goto error;
             }
 
-            virCommandAddArg(cmd, "-chardev");
             if (!(devstr = qemuBuildChrChardevStr(&channel->source,
                                                   channel->info.alias,
-                                                  caps)))
+                                                  caps, cmd, driver, fdset,
+                                                  &channel->info.fdset)))
                 goto error;
-            virCommandAddArg(cmd, devstr);
+            virCommandAddArgList(cmd, "-chardev", devstr, NULL);
             VIR_FREE(devstr);
 
             addr = virSocketAddrFormat(channel->target.addr);
@@ -6422,12 +6570,13 @@ qemuBuildCommandLine(virConnectPtr conn,
                  * the newer -chardev interface.  */
                 ;
             } else {
-                virCommandAddArg(cmd, "-chardev");
                 if (!(devstr = qemuBuildChrChardevStr(&channel->source,
                                                       channel->info.alias,
-                                                      caps)))
+                                                      caps, cmd, driver,
+                                                      fdset,
+                                                      &channel->info.fdset)))
                     goto error;
-                virCommandAddArg(cmd, devstr);
+                virCommandAddArgList(cmd, "-chardev", devstr, NULL);
                 VIR_FREE(devstr);
             }
 
@@ -6460,12 +6609,12 @@ qemuBuildCommandLine(virConnectPtr conn,
                 goto error;
             }
 
-            virCommandAddArg(cmd, "-chardev");
             if (!(devstr = qemuBuildChrChardevStr(&console->source,
                                                   console->info.alias,
-                                                  caps)))
+                                                  caps, cmd, driver, fdset,
+                                                  &console->info.fdset)))
                 goto error;
-            virCommandAddArg(cmd, devstr);
+            virCommandAddArgList(cmd, "-chardev", devstr, NULL);
             VIR_FREE(devstr);
 
             virCommandAddArg(cmd, "-device");
@@ -6482,12 +6631,12 @@ qemuBuildCommandLine(virConnectPtr conn,
                 goto error;
             }
 
-            virCommandAddArg(cmd, "-chardev");
             if (!(devstr = qemuBuildChrChardevStr(&console->source,
                                                   console->info.alias,
-                                                  caps)))
+                                                  caps, cmd, driver, fdset,
+                                                  &console->info.fdset)))
                 goto error;
-            virCommandAddArg(cmd, devstr);
+            virCommandAddArgList(cmd, "-chardev", devstr, NULL);
             VIR_FREE(devstr);
 
             virCommandAddArg(cmd, "-device");
@@ -6824,14 +6973,14 @@ qemuBuildCommandLine(virConnectPtr conn,
         virDomainRedirdevDefPtr redirdev = def->redirdevs[i];
         char *devstr;
 
-        virCommandAddArg(cmd, "-chardev");
         if (!(devstr = qemuBuildChrChardevStr(&redirdev->source.chr,
                                               redirdev->info.alias,
-                                              caps))) {
+                                              caps, cmd, driver, fdset,
+                                              &redirdev->info.fdset))) {
             goto error;
         }
 
-        virCommandAddArg(cmd, devstr);
+        virCommandAddArgList(cmd, "-chardev", devstr, NULL);
         VIR_FREE(devstr);
 
         if (!qemuCapsGet(caps, QEMU_CAPS_DEVICE))
Index: libvirt/src/qemu/qemu_command.h
===================================================================
--- libvirt.orig/src/qemu/qemu_command.h
+++ libvirt/src/qemu/qemu_command.h
@@ -30,6 +30,7 @@
 # include "qemu_conf.h"
 # include "qemu_domain.h"
 # include "qemu_capabilities.h"
+# include "virbitmap.h"
 
 /* Config type for XML import/export conversions */
 # define QEMU_CONFIG_FORMAT_ARGV "qemu-argv"
@@ -58,7 +59,8 @@ virCommandPtr qemuBuildCommandLine(virCo
                                    const char *migrateFrom,
                                    int migrateFd,
                                    virDomainSnapshotObjPtr current_snapshot,
-                                   enum virNetDevVPortProfileOp vmop)
+                                   enum virNetDevVPortProfileOp vmop,
+                                   virBitmapPtr fdset)
     ATTRIBUTE_NONNULL(1);
 
 /* Generate string for arch-specific '-device' parameter */
@@ -95,9 +97,16 @@ char *qemuDeviceDriveHostAlias(virDomain
 char *qemuBuildDriveStr(virConnectPtr conn,
                         virDomainDiskDefPtr disk,
                         bool bootable,
-                        qemuCapsPtr caps);
+                        qemuCapsPtr caps,
+                        virCommandPtr cmd,
+                        virQEMUDriverPtr driver,
+                        virBitmapPtr fdset);
+
 char *qemuBuildFSStr(virDomainFSDefPtr fs,
-                     qemuCapsPtr caps);
+                     qemuCapsPtr caps,
+                     virCommandPtr cmd,
+                     virQEMUDriverPtr driver,
+                     virBitmapPtr fdset);
 
 /* Current, best practice */
 char * qemuBuildDriveDevStr(virDomainDefPtr def,
Index: libvirt/src/qemu/qemu_driver.c
===================================================================
--- libvirt.orig/src/qemu/qemu_driver.c
+++ libvirt/src/qemu/qemu_driver.c
@@ -2679,7 +2679,7 @@ qemuCompressProgramName(int compress)
 
 /* Internal function to properly create or open existing files, with
  * ownership affected by qemu driver setup.  */
-static int
+int
 qemuOpenFile(virQEMUDriverPtr driver, const char *path, int oflags,
              bool *needUnlink, bool *bypassSecurityDriver)
 {
@@ -5437,7 +5437,8 @@ static char *qemuDomainXMLToNative(virCo
 
     if (!(cmd = qemuBuildCommandLine(conn, driver, def,
                                      &monConfig, monitor_json, caps,
-                                     NULL, -1, NULL, VIR_NETDEV_VPORT_PROFILE_OP_NO_OP)))
+                                     NULL, -1, NULL, VIR_NETDEV_VPORT_PROFILE_OP_NO_OP,
+                                     NULL)))
         goto cleanup;
 
     ret = virCommandToString(cmd);
Index: libvirt/src/qemu/qemu_hotplug.c
===================================================================
--- libvirt.orig/src/qemu/qemu_hotplug.c
+++ libvirt/src/qemu/qemu_hotplug.c
@@ -262,7 +262,8 @@ int qemuDomainAttachPciDiskDevice(virCon
         if (qemuAssignDeviceDiskAlias(vm->def, disk, priv->caps) < 0)
             goto error;
 
-        if (!(drivestr = qemuBuildDriveStr(conn, disk, false, priv->caps)))
+        if (!(drivestr = qemuBuildDriveStr(conn, disk, false, priv->caps,
+                                           NULL, driver, priv->fdset)))
             goto error;
 
         if (!(devstr = qemuBuildDriveDevStr(NULL, disk, 0, priv->caps)))
@@ -503,7 +504,8 @@ int qemuDomainAttachSCSIDisk(virConnectP
             goto error;
     }
 
-    if (!(drivestr = qemuBuildDriveStr(conn, disk, false, priv->caps)))
+    if (!(drivestr = qemuBuildDriveStr(conn, disk, false, priv->caps, NULL,
+                                       driver, priv->fdset)))
         goto error;
 
     for (i = 0 ; i <= disk->info.addr.drive.controller ; i++) {
@@ -622,7 +624,8 @@ int qemuDomainAttachUsbMassstorageDevice
     if (qemuCapsGet(priv->caps, QEMU_CAPS_DEVICE)) {
         if (qemuAssignDeviceDiskAlias(vm->def, disk, priv->caps) < 0)
             goto error;
-        if (!(drivestr = qemuBuildDriveStr(conn, disk, false, priv->caps)))
+        if (!(drivestr = qemuBuildDriveStr(conn, disk, false, priv->caps,
+                                           NULL, driver, priv->fdset)))
             goto error;
         if (!(devstr = qemuBuildDriveDevStr(NULL, disk, 0, priv->caps)))
             goto error;
Index: libvirt/src/qemu/qemu_process.c
===================================================================
--- libvirt.orig/src/qemu/qemu_process.c
+++ libvirt/src/qemu/qemu_process.c
@@ -3779,7 +3779,8 @@ int qemuProcessStart(virConnectPtr conn,
     VIR_DEBUG("Building emulator command line");
     if (!(cmd = qemuBuildCommandLine(conn, driver, vm->def, priv->monConfig,
                                      priv->monJSON != 0, priv->caps,
-                                     migrateFrom, stdin_fd, snapshot, vmop)))
+                                     migrateFrom, stdin_fd, snapshot, vmop,
+                                     priv->fdset)))
         goto cleanup;
 
     /* now that we know it is about to start call the hook if present */
Index: libvirt/tests/qemuxml2argvtest.c
===================================================================
--- libvirt.orig/tests/qemuxml2argvtest.c
+++ libvirt/tests/qemuxml2argvtest.c
@@ -18,6 +18,7 @@
 # include "qemu/qemu_domain.h"
 # include "datatypes.h"
 # include "cpu/cpu_map.h"
+# include "virbitmap.h"
 
 # include "testutilsqemu.h"
 
@@ -151,7 +152,8 @@ static int testCompareXMLToArgvFiles(con
     if (!(cmd = qemuBuildCommandLine(conn, &driver, vmdef, &monitor_chr,
                                      (flags & FLAG_JSON), extraFlags,
                                      migrateFrom, migrateFd, NULL,
-                                     VIR_NETDEV_VPORT_PROFILE_OP_NO_OP))) {
+                                     VIR_NETDEV_VPORT_PROFILE_OP_NO_OP,
+                                     NULL))) {
         if (flags & FLAG_EXPECT_FAILURE) {
             ret = 0;
             virResetLastError();
Index: libvirt/tests/qemuxmlnstest.c
===================================================================
--- libvirt.orig/tests/qemuxmlnstest.c
+++ libvirt/tests/qemuxmlnstest.c
@@ -17,6 +17,7 @@
 # include "qemu/qemu_domain.h"
 # include "datatypes.h"
 # include "cpu/cpu_map.h"
+# include "virbitmap.h"
 
 # include "testutilsqemu.h"
 
@@ -41,10 +42,14 @@ static int testCompareXMLToArgvFiles(con
     char *log = NULL;
     char *emulator = NULL;
     virCommandPtr cmd = NULL;
+    virBitmapPtr fdset;
 
     if (!(conn = virGetConnect()))
         goto fail;
 
+    if (!(fdset = virBitmapNew(4096)))
+        goto fail;
+
     len = virtTestLoadFile(cmdline, &expectargv);
     if (len < 0)
         goto fail;
@@ -110,7 +115,8 @@ static int testCompareXMLToArgvFiles(con
     if (!(cmd = qemuBuildCommandLine(conn, &driver,
                                      vmdef, &monitor_chr, json, extraFlags,
                                      migrateFrom, migrateFd, NULL,
-                                     VIR_NETDEV_VPORT_PROFILE_OP_NO_OP)))
+                                     VIR_NETDEV_VPORT_PROFILE_OP_NO_OP,
+                                     fdset)))
         goto fail;
 
     if (!!virGetLastError() != expectError) {
@@ -151,6 +157,7 @@ static int testCompareXMLToArgvFiles(con
     virCommandFree(cmd);
     virDomainDefFree(vmdef);
     virObjectUnref(conn);
+    virBitmapFree(fdset);
     return ret;
 }
 
Index: libvirt/src/qemu/qemu_driver.h
===================================================================
--- libvirt.orig/src/qemu/qemu_driver.h
+++ libvirt/src/qemu/qemu_driver.h
@@ -24,6 +24,10 @@
 #ifndef __QEMU_DRIVER_H__
 # define __QEMU_DRIVER_H__
 
+# include "qemu_conf.h"
+
 int qemuRegister(void);
+int qemuOpenFile(virQEMUDriverPtr driver, const char *path, int oflags,
+                 bool *needUnlink, bool *bypassSecurityDriver);
 
 #endif /* __QEMU_DRIVER_H__ */
Index: libvirt/src/conf/domain_conf.h
===================================================================
--- libvirt.orig/src/conf/domain_conf.h
+++ libvirt/src/conf/domain_conf.h
@@ -262,6 +262,7 @@ struct _virDomainDeviceInfo {
      * to consider the new fields
      */
     char *alias;
+    unsigned int fdset; /* > 0; "-add-fd set=%u,fd=123", fdsetnum */
     int type;
     union {
         virDevicePCIAddress pci;
Index: libvirt/src/conf/domain_conf.c
===================================================================
--- libvirt.orig/src/conf/domain_conf.c
+++ libvirt/src/conf/domain_conf.c
@@ -2219,7 +2219,10 @@ virDomainDeviceInfoFormat(virBufferPtr b
 
     if (info->alias &&
         !(flags & VIR_DOMAIN_XML_INACTIVE)) {
-        virBufferAsprintf(buf, "      <alias name='%s'/>\n", info->alias);
+        virBufferAsprintf(buf, "      <alias name='%s'", info->alias);
+        if (info->fdset > 0)
+            virBufferAsprintf(buf, " fdset='%u'", info->fdset);
+        virBufferAddLit(buf, "/>\n");
     }
 
     if (info->mastertype == VIR_DOMAIN_CONTROLLER_MASTER_USB) {
@@ -2597,6 +2600,7 @@ virDomainDeviceInfoParseXML(xmlNodePtr n
     xmlNodePtr boot = NULL;
     xmlNodePtr rom = NULL;
     char *type = NULL;
+    char *fdset = NULL;
     int ret = -1;
 
     virDomainDeviceInfoClear(info);
@@ -2627,9 +2631,18 @@ virDomainDeviceInfoParseXML(xmlNodePtr n
         cur = cur->next;
     }
 
-    if (alias)
+    if (alias) {
         info->alias = virXMLPropString(alias, "name");
 
+        fdset = virXMLPropString(alias, "fdset");
+        if (fdset && virStrToLong_ui(fdset, NULL, 10, &info->fdset) < 0) {
+            virReportError(VIR_ERR_INTERNAL_ERROR,
+                           _("incorrect fdset '%s', expecting positive integer"),
+                           fdset);
+            goto cleanup;
+        }
+    }
+
     if (master) {
         info->mastertype = VIR_DOMAIN_CONTROLLER_MASTER_USB;
         if (virDomainDeviceUSBMasterParseXML(master, &info->master.usb) < 0)
@@ -2716,6 +2729,7 @@ cleanup:
     if (ret == -1)
         VIR_FREE(info->alias);
     VIR_FREE(type);
+    VIR_FREE(fdset);
     return ret;
 }
 
@@ -10563,7 +10577,7 @@ static virDomainObjPtr virDomainObjParse
     VIR_FREE(nodes);
 
     if (caps->privateDataXMLParse &&
-        ((caps->privateDataXMLParse)(ctxt, obj->privateData)) < 0)
+        ((caps->privateDataXMLParse)(ctxt, obj->privateData, obj->def)) < 0)
         goto error;
 
     return obj;
Index: libvirt/src/conf/capabilities.h
===================================================================
--- libvirt.orig/src/conf/capabilities.h
+++ libvirt/src/conf/capabilities.h
@@ -149,6 +149,9 @@ struct _virDomainXMLNamespace {
     virDomainDefNamespaceHref href;
 };
 
+typedef struct _virDomainDef virDomainDef;
+typedef virDomainDef *virDomainDefPtr;
+
 typedef struct _virCaps virCaps;
 typedef virCaps* virCapsPtr;
 struct _virCaps {
@@ -164,7 +167,7 @@ struct _virCaps {
     void *(*privateDataAllocFunc)(void);
     void (*privateDataFreeFunc)(void *);
     int (*privateDataXMLFormat)(virBufferPtr, void *);
-    int (*privateDataXMLParse)(xmlXPathContextPtr, void *);
+    int (*privateDataXMLParse)(xmlXPathContextPtr, void *, virDomainDefPtr);
     bool hasWideScsiBus;
     const char *defaultInitPath;
 
Index: libvirt/src/lxc/lxc_domain.c
===================================================================
--- libvirt.orig/src/lxc/lxc_domain.c
+++ libvirt/src/lxc/lxc_domain.c
@@ -57,7 +57,8 @@ static int virLXCDomainObjPrivateXMLForm
     return 0;
 }
 
-static int virLXCDomainObjPrivateXMLParse(xmlXPathContextPtr ctxt, void *data)
+static int virLXCDomainObjPrivateXMLParse(xmlXPathContextPtr ctxt, void *data,
+                                          virDomainDefPtr def ATTRIBUTE_UNUSED)
 {
     virLXCDomainObjPrivatePtr priv = data;
     unsigned long long thepid;
Index: libvirt/src/qemu/qemu_domain.c
===================================================================
--- libvirt.orig/src/qemu/qemu_domain.c
+++ libvirt/src/qemu/qemu_domain.c
@@ -336,7 +336,29 @@ static int qemuDomainObjPrivateXMLFormat
     return 0;
 }
 
-static int qemuDomainObjPrivateXMLParse(xmlXPathContextPtr ctxt, void *data)
+static int qemuDomainRebuildFDSet(virDomainDefPtr def ATTRIBUTE_UNUSED,
+                                  virDomainDeviceDefPtr dev ATTRIBUTE_UNUSED,
+                                  virDomainDeviceInfoPtr info,
+                                  void *opaque)
+{
+    virBitmapPtr fdset = opaque;
+
+    if (info->fdset > 0) {
+        VIR_DEBUG("Found fdset %u from domain '%s'",
+                  info->fdset, def->name);
+        if (virBitmapSetBit(fdset, info->fdset)) {
+            virReportError(VIR_ERR_INTERNAL_ERROR,
+                           _("File descriptor set cannot set bit %u"),
+                           info->fdset);
+            return -1;
+        }
+    }
+
+    return 0;
+}
+
+static int qemuDomainObjPrivateXMLParse(xmlXPathContextPtr ctxt, void *data,
+                                        virDomainDefPtr def)
 {
     qemuDomainObjPrivatePtr priv = data;
     char *monitorpath;
@@ -478,6 +500,8 @@ static int qemuDomainObjPrivateXMLParse(
 
     priv->fakeReboot = virXPathBoolean("boolean(./fakereboot)", ctxt) == 1;
 
+    virDomainDeviceInfoIterate(def, qemuDomainRebuildFDSet, priv->fdset);
+
     return 0;
 
 error: