[PATCH 11/12] hw/xen: automatically assign device index to block devices

[David Woodhouse <dwmw2@infradead.org>]

From: David Woodhouse <dwmw@amazon.co.uk>

There's no need to force the user to assign a vdev. We can automatically
assign one, starting at xvda and searching until we find the first disk
name that's unused.

This means we can now allow '-drive if=xen,file=xxx' to work without an
explicit separate -driver argument, just like if=virtio.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 blockdev.c           | 15 ++++++++++++---
 hw/block/xen-block.c | 25 +++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index 325b7a3bef..9dec4c9c74 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -255,13 +255,13 @@ void drive_check_orphaned(void)
          * Ignore default drives, because we create certain default
          * drives unconditionally, then leave them unclaimed.  Not the
          * users fault.
-         * Ignore IF_VIRTIO, because it gets desugared into -device,
-         * so we can leave failing to -device.
+         * Ignore IF_VIRTIO or IF_XEN, because it gets desugared into
+         * -device, so we can leave failing to -device.
          * Ignore IF_NONE, because leaving unclaimed IF_NONE remains
          * available for device_add is a feature.
          */
         if (dinfo->is_default || dinfo->type == IF_VIRTIO
-            || dinfo->type == IF_NONE) {
+            || dinfo->type == IF_XEN || dinfo->type == IF_NONE) {
             continue;
         }
         if (!blk_get_attached_dev(blk)) {
@@ -977,6 +977,15 @@ DriveInfo *drive_new(QemuOpts *all_opts, BlockInterfaceType block_default_type,
         qemu_opt_set(devopts, "driver", "virtio-blk", &error_abort);
         qemu_opt_set(devopts, "drive", qdict_get_str(bs_opts, "id"),
                      &error_abort);
+    } else if (type == IF_XEN) {
+        QemuOpts *devopts;
+        devopts = qemu_opts_create(qemu_find_opts("device"), NULL, 0,
+                                   &error_abort);
+        qemu_opt_set(devopts, "driver",
+                     (media == MEDIA_CDROM) ? "xen-cdrom" : "xen-disk",
+                     &error_abort);
+        qemu_opt_set(devopts, "drive", qdict_get_str(bs_opts, "id"),
+                     &error_abort);
     }
 
     filename = qemu_opt_get(legacy_opts, "file");
diff --git a/hw/block/xen-block.c b/hw/block/xen-block.c
index 9262338535..20fa783cbe 100644
--- a/hw/block/xen-block.c
+++ b/hw/block/xen-block.c
@@ -34,6 +34,31 @@ static char *xen_block_get_name(XenDevice *xendev, Error **errp)
     XenBlockDevice *blockdev = XEN_BLOCK_DEVICE(xendev);
     XenBlockVdev *vdev = &blockdev->props.vdev;
 
+    if (blockdev->props.vdev.type == XEN_BLOCK_VDEV_TYPE_INVALID) {
+        char name[11];
+        int disk = 0;
+        unsigned long idx;
+
+        /* Find an unoccupied device name */
+        while (disk < (1 << 20)) {
+            if (disk < (1 << 4)) {
+                idx = (202 << 8) | (disk << 4);
+            } else {
+                idx = (1 << 28) | (disk << 8);
+            }
+            snprintf(name, sizeof(name), "%lu", idx);
+            if (!xen_backend_exists("qdisk", name)) {
+                vdev->type = XEN_BLOCK_VDEV_TYPE_XVD;
+                vdev->partition = 0;
+                vdev->disk = disk;
+                vdev->number = idx;
+                return g_strdup(name);
+            }
+            disk++;
+        }
+        error_setg(errp, "cannot find device vdev for block device");
+        return NULL;
+    }
     return g_strdup_printf("%lu", vdev->number);
 }
 
-- 
2.40.1