launch: direct: Calculate appliance root correctly when iface drives are added (RHBZ#975797).

This also changes guestfs___appliance_command_line to allow
appliance_dev parameter to be NULL.  Previously a bogus root=
parameter could be passed.

src/launch-direct.c

@@ -76,6 +76,7 @@ free_regexps (void)
 }
 
 static int is_openable (guestfs_h *g, const char *path, int flags);
+static char *make_appliance_dev (guestfs_h *g, int virtio_scsi);
 static void print_qemu_command_line (guestfs_h *g, char **argv);
 static int qemu_supports (guestfs_h *g, const char *option);
 static int qemu_supports_device (guestfs_h *g, const char *device_name);
@@ -175,6 +176,7 @@ launch_direct (guestfs_h *g, const char *arg)
   struct sockaddr_un addr;
   CLEANUP_FREE char *kernel = NULL, *initrd = NULL, *appliance = NULL;
   int has_appliance_drive;
+  CLEANUP_FREE char *appliance_dev = NULL;
   uint32_t size;
   CLEANUP_FREE void *buf = NULL;
 
@@ -313,8 +315,6 @@ launch_direct (guestfs_h *g, const char *arg)
       }
     }
 
-    char appliance_dev[64] = "/dev/Xd";
-
     /* Add the ext2 appliance drive (after all the drives). */
     if (has_appliance_drive) {
       const char *cachemode = "";
@@ -337,8 +337,7 @@ launch_direct (guestfs_h *g, const char *arg)
         add_cmdline (g, "scsi-hd,drive=appliance");
       }
 
-      appliance_dev[5] = virtio_scsi ? 's' : 'v';
-      guestfs___drive_name (g->nr_drives, &appliance_dev[7]);
+      appliance_dev = make_appliance_dev (g, virtio_scsi);
     }
 
     /* The qemu -machine option (added 2010-12) is a bit more sane
@@ -696,6 +695,40 @@ launch_direct (guestfs_h *g, const char *arg)
   return -1;
 }
 
+/* Calculate the appliance device name.
+ *
+ * The easy thing would be to use g->nr_drives (indeed, that's what we
+ * used to do).  However this breaks if some of the drives being added
+ * use the deprecated 'iface' parameter.  To further add confusion,
+ * the format of the 'iface' parameter has never been defined, but
+ * given existing usage we can assume it has one of only three values:
+ * NULL, "ide" or "virtio" (which means virtio-blk).  See RHBZ#975797.
+ */
+static char *
+make_appliance_dev (guestfs_h *g, int virtio_scsi)
+{
+  size_t i, index = 0;
+  struct drive *drv;
+  char dev[64] = "/dev/Xd";
+
+  /* Calculate the index of the drive. */
+  ITER_DRIVES (g, i, drv) {
+    if (virtio_scsi) {
+      if (drv->iface == NULL || STREQ (drv->iface, "ide"))
+        index++;
+    }
+    else /* virtio-blk */ {
+      if (drv->iface == NULL || STRNEQ (drv->iface, "virtio"))
+        index++;
+    }
+  }
+
+  dev[5] = virtio_scsi ? 's' : 'v';
+  guestfs___drive_name (index, &dev[7]);
+
+  return safe_strdup (g, dev);  /* Caller frees. */
+}
+
 /* This is called from the forked subprocess just before qemu runs, so
  * it can just print the message straight to stderr, where it will be
  * picked up and funnelled through the usual appliance event API.

src/launch.c

@@ -302,11 +302,15 @@ char *
 guestfs___appliance_command_line (guestfs_h *g, const char *appliance_dev,
                                   int flags)
 {
+  char root[64] = "";
   char *term = getenv ("TERM");
   char *ret;
   bool tcg = flags & APPLIANCE_COMMAND_LINE_IS_TCG;
   char lpj_s[64] = "";
 
+  if (appliance_dev)
+    snprintf (root, sizeof root, " root=%s", appliance_dev);
+
   if (tcg) {
     int lpj = guestfs___get_lpj (g);
     if (lpj > 0)
@@ -326,13 +330,13 @@ guestfs___appliance_command_line (guestfs_h *g, const char *appliance_dev,
      " acpi=off"        /* we don't need ACPI, turn it off */
      " printk.time=1"   /* display timestamp before kernel messages */
      " cgroup_disable=memory"   /* saves us about 5 MB of RAM */
-     " root=%s"                 /* root (appliance_dev) */
+     "%s"                       /* root=appliance_dev */
      " %s"                      /* selinux */
      "%s"                       /* verbose */
      " TERM=%s"                 /* TERM environment variable */
      "%s%s",                    /* append */
      lpj_s,
-     appliance_dev,
+     root,
      g->selinux ? "selinux=1 enforcing=0" : "selinux=0",
      g->verbose ? " guestfs_verbose=1" : "",
      term ? term : "linux",