[PATCH v4 7/8] 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.


Changes on v4:
- improve error handling and exit paths in libxl__device_disk_local_attach.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
---
 tools/hotplug/Linux/init.d/sysconfig.xencommons |    3 +
 tools/hotplug/Linux/init.d/xencommons           |    3 +
 tools/libxl/libxl_internal.c                    |   63 +++++++++++++++++++----
 tools/libxl/libxl_internal.h                    |    2 +
 4 files changed, 60 insertions(+), 11 deletions(-)

diff --git a/tools/hotplug/Linux/init.d/sysconfig.xencommons b/tools/hotplug/Linux/init.d/sysconfig.xencommons
index 6543204..0f3b9ad 100644
--- a/tools/hotplug/Linux/init.d/sysconfig.xencommons
+++ b/tools/hotplug/Linux/init.d/sysconfig.xencommons
@@ -12,3 +12,6 @@
 
 # Running xenbackendd in debug mode
 #XENBACKENDD_DEBUG=[yes|on|1]
+
+# qemu path and log file
+#QEMU_XEN=/usr/lib/xen/bin/qemu-system-i386
diff --git a/tools/hotplug/Linux/init.d/xencommons b/tools/hotplug/Linux/init.d/xencommons
index 2f81ea2..9dda6e2 100644
--- a/tools/hotplug/Linux/init.d/xencommons
+++ b/tools/hotplug/Linux/init.d/xencommons
@@ -104,6 +104,9 @@ 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
+	$QEMU_XEN -xen-domid 0 -xen-attach -name dom0 -nographic -M xenpv -daemonize -monitor /dev/null
 }
 do_stop () {
         echo Stopping xenconsoled
diff --git a/tools/libxl/libxl_internal.c b/tools/libxl/libxl_internal.c
index ac73070..bb75491 100644
--- a/tools/libxl/libxl_internal.c
+++ b/tools/libxl/libxl_internal.c
@@ -510,6 +510,7 @@ _hidden char * libxl__device_disk_local_attach(libxl__gc *gc,
     libxl_ctx *ctx = gc->owner;
     char *dev = NULL;
     int rc;
+    xs_transaction_t t = XBT_NULL;
     libxl_device_disk *tmpdisk = libxl__zalloc(gc, sizeof(libxl_device_disk));
     if (tmpdisk == NULL) goto out;
 
@@ -554,13 +555,40 @@ _hidden char * libxl__device_disk_local_attach(libxl__gc *gc,
             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;
+                do {
+                    t = xs_transaction_start(ctx->xsh);
+                    if (t == XBT_NULL) {
+                        LIBXL__LOG(ctx, LIBXL__LOG_ERROR,
+                                "failed to start a xenstore transaction");
+                        goto out;
+                    }
+                    tmpdisk->vdev = libxl__alloc_vdev(gc,
+                            LIBXL_TOOLSTACK_DOMID, blkdev_start, t);
+                    if (tmpdisk->vdev == NULL) {
+                        LIBXL__LOG(ctx, LIBXL__LOG_ERROR,
+                                "libxl__alloc_vdev failed\n");
+                        goto out;
+                    }
+                    if (libxl__device_disk_add_t(gc, LIBXL_TOOLSTACK_DOMID,
+                                t, tmpdisk)) {
+                        LIBXL__LOG(ctx, LIBXL__LOG_ERROR,
+                                "libxl_device_disk_add failed\n");
+                        goto out;
+                    }
+                    rc = xs_transaction_end(ctx->xsh, t, 0);
+                } while (rc == 0 && errno == EAGAIN);
+                t = XBT_NULL;
+                if (rc == 0) {
+                    LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR,
+                            "xenstore transaction failed");
+                    goto out;
+                }
+                dev = GCSPRINTF("/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 "
@@ -569,17 +597,30 @@ _hidden char * libxl__device_disk_local_attach(libxl__gc *gc,
     }
 
  out:
+    if (t != XBT_NULL)
+        xs_transaction_end(ctx->xsh, t, 1);
     return dev;
 }
 
 _hidden int libxl__device_disk_local_detach(libxl__gc *gc, 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->vdev != NULL) {
+                libxl_device_disk_remove(gc->owner, LIBXL_TOOLSTACK_DOMID,
+                        disk, 0);
+                return libxl_device_disk_destroy(gc->owner,
+                        LIBXL_TOOLSTACK_DOMID, 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;
 }
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index ed145ab..dfd7b49 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -77,6 +77,8 @@
 #define LIBXL_PV_EXTRA_MEMORY 1024
 #define LIBXL_HVM_EXTRA_MEMORY 2048
 #define LIBXL_MIN_DOM0_MEM (128*1024)
+/* use 0 as the domid of the toolstack domain for now */
+#define LIBXL_TOOLSTACK_DOMID 0
 #define QEMU_SIGNATURE "DeviceModelRecord0002"
 #define STUBDOM_CONSOLE_LOGGING 0
 #define STUBDOM_CONSOLE_SAVE 1
-- 
1.7.2.5