[PATCH 6/6] xl/libxl: implement QDISK libxl_device_disk_local_attach

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

- Spawn a QEMU instance at boot time to handle disk local attach
requests.

- Implement libxl_device_disk_local_attach for QDISKs in terms of a
regular disk attach with the frontend and backend running in the same
domain.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
---
 tools/hotplug/Linux/init.d/sysconfig.xencommons |    4 ++
 tools/hotplug/Linux/init.d/xencommons           |    4 ++
 tools/libxl/libxl.c                             |   46 +++++++++++++++++-----
 3 files changed, 43 insertions(+), 11 deletions(-)

diff --git a/tools/hotplug/Linux/init.d/sysconfig.xencommons b/tools/hotplug/Linux/init.d/sysconfig.xencommons
index 6543204..28cf2eb 100644
--- a/tools/hotplug/Linux/init.d/sysconfig.xencommons
+++ b/tools/hotplug/Linux/init.d/sysconfig.xencommons
@@ -12,3 +12,7 @@
 
 # Running xenbackendd in debug mode
 #XENBACKENDD_DEBUG=[yes|on|1]
+
+# qemu path and log file
+#QEMU_XEN=/usr/lib/xen/bin/qemu-system-i386
+#QEMU_XEN_LOG=/var/log/xen/qemu-dm-dom0.log
diff --git a/tools/hotplug/Linux/init.d/xencommons b/tools/hotplug/Linux/init.d/xencommons
index 6c72dd8..f328492 100644
--- a/tools/hotplug/Linux/init.d/xencommons
+++ b/tools/hotplug/Linux/init.d/xencommons
@@ -103,6 +103,10 @@ do_start () {
 	xenconsoled --pid-file=$XENCONSOLED_PIDFILE $XENCONSOLED_ARGS
 	test -z "$XENBACKENDD_DEBUG" || XENBACKENDD_ARGS="-d"
 	test "`uname`" != "NetBSD" || xenbackendd $XENBACKENDD_ARGS
+	echo Starting QEMU as disk backend for dom0
+	test -z "$QEMU_XEN" && QEMU_XEN=/usr/lib/xen/bin/qemu-system-i386
+	test -z "$QEMU_XEN_LOG" && QEMU_XEN_LOG=/var/log/xen/qemu-dm-dom0.log
+	$QEMU_XEN -xen-domid 0 -xen-attach -name dom0 -nographic -M xenpv -daemonize &>$QEMU_XEN_LOG
 }
 do_stop () {
         echo Stopping xenconsoled
diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index fa7898a..4c89a56 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -1767,13 +1767,30 @@ char * libxl_device_disk_local_attach(libxl_ctx *ctx, const libxl_device_disk *d
             break;
         case LIBXL_DISK_BACKEND_QDISK:
             if (tmpdisk->format != LIBXL_DISK_FORMAT_RAW) {
-                LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "cannot locally"
-                           " attach a qdisk image if the format is not raw");
-                break;
+                xs_transaction_t t;
+retry_transaction:
+                t = xs_transaction_start(ctx->xsh);
+                /* use 0 as the domid of the toolstack domain for now */
+                tmpdisk->vdev = libxl__alloc_vdev(gc, 0, t, tmpdisk);
+                if (tmpdisk->vdev == NULL) {
+                    LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "libxl__alloc_vdev failed\n");
+                    xs_transaction_end(ctx->xsh, t, 1);
+                    goto out;
+                }
+                if (libxl__device_disk_add_t(gc, 0, t, tmpdisk)) {
+                    LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "libxl_device_disk_add failed\n");
+                    xs_transaction_end(ctx->xsh, t, 1);
+                    goto out;
+                }
+                if (!xs_transaction_end(ctx->xsh, t, 0))
+                    if (errno == EAGAIN)
+                        goto retry_transaction;
+                dev = libxl__sprintf(gc, "/dev/%s", tmpdisk->vdev);
+            } else {
+                dev = tmpdisk->pdev_path;
             }
             LIBXL__LOG(ctx, LIBXL__LOG_DEBUG, "locally attaching qdisk %s\n",
-                       disk->pdev_path);
-            dev = tmpdisk->pdev_path;
+                       dev);
             break;
         default:
             LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "unrecognized disk backend "
@@ -1792,12 +1809,19 @@ char * libxl_device_disk_local_attach(libxl_ctx *ctx, const libxl_device_disk *d
 
 int libxl_device_disk_local_detach(libxl_ctx *ctx, libxl_device_disk *disk)
 {
-    /* Nothing to do for PHYSTYPE_PHY. */
-
-    /*
-     * For other device types assume that the blktap2 process is
-     * needed by the soon to be started domain and do nothing.
-     */
+    switch (disk->backend) {
+        case LIBXL_DISK_BACKEND_QDISK:
+            if (disk->format != LIBXL_DISK_FORMAT_RAW)
+                return libxl_device_disk_destroy(ctx, 0, disk);
+            break;
+        default:
+            /*
+             * Nothing to do for PHYSTYPE_PHY.
+             * For other device types assume that the blktap2 process is
+             * needed by the soon to be started domain and do nothing.
+             */
+            break;
+    }
 
     return 0;
 }
-- 
1.7.2.5