appliance: Pass root=UUID=<uuid> instead of appliance device name (RHBZ#1804207).

Appliance device names are not reliable since the kernel no longer
enumerates virtio-scsi devices serially.  Instead get the UUID of the
appliance and pass this as the parameter.

Note this requires supermin >= 5.1.18 (from around July 2017).

docs/guestfs-building.pod

@@ -83,7 +83,7 @@ I<Required>.
 I<Required>.  The following features must be enabled:
 C<virtio-pci>, C<virtio-serial>, C<virtio-block>, C<virtio-net>.
 
-=item supermin E<ge> 5.1.0
+=item supermin E<ge> 5.1.18
 
 I<Required>.  For alternatives, see L</USING A PREBUILT BINARY APPLIANCE>
 below.

lib/appliance-kcmdline.c

@@ -26,8 +26,10 @@
 #include <stdlib.h>
 #include <stdbool.h>
 #include <string.h>
+#include <unistd.h>
 
 #include "c-ctype.h"
+#include "ignore-value.h"
 
 #include "guestfs.h"
 #include "guestfs-internal.h"
@@ -54,15 +56,53 @@
 #define EARLYPRINTK "earlyprintk=pl011,0x9000000"
 #endif
 
+COMPILE_REGEXP (re_uuid, "UUID=([-0-9a-f]+)", 0)
+
+static void
+read_uuid (guestfs_h *g, void *retv, const char *line, size_t len)
+{
+  char **ret = retv;
+
+  *ret = match1 (g, line, re_uuid);
+}
+
+/**
+ * Given a disk image containing an extX filesystem, return the UUID.
+ * The L<file(1)> command does the hard work.
+ */
+static char *
+get_root_uuid (guestfs_h *g, const char *appliance)
+{
+  CLEANUP_CMD_CLOSE struct command *cmd = guestfs_int_new_command (g);
+  char *ret = NULL;
+  int r;
+
+  guestfs_int_cmd_add_arg (cmd, "file");
+  guestfs_int_cmd_add_arg (cmd, "--");
+  guestfs_int_cmd_add_arg (cmd, appliance);
+  guestfs_int_cmd_set_stdout_callback (cmd, read_uuid, &ret, 0);
+  r = guestfs_int_cmd_run (cmd);
+  if (r == -1) {
+    if (ret) free (ret);
+    return NULL;
+  }
+  if (!WIFEXITED (r) || WEXITSTATUS (r) != 0) {
+    guestfs_int_external_command_failed (g, r, "file", NULL);
+    if (ret) free (ret);
+    return NULL;
+  }
+
+  return ret;
+}
+
 /**
  * Construct the Linux command line passed to the appliance.  This is
  * used by the C<direct> and C<libvirt> backends, and is simply
  * located in this file because it's a convenient place for this
  * common code.
  *
- * The C<appliance_dev> parameter must be the full device name of the
- * appliance disk and must have already been adjusted to take into
- * account virtio-blk or virtio-scsi; eg C</dev/sdb>.
+ * The C<appliance> parameter is the filename of the appliance
+ * (could be NULL) from which we obtain the root UUID.
  *
  * The C<flags> parameter can contain the following flags logically
  * or'd together (or 0):
@@ -80,7 +120,8 @@
  * be freed by the caller.
  */
 char *
-guestfs_int_appliance_command_line (guestfs_h *g, const char *appliance_dev,
+guestfs_int_appliance_command_line (guestfs_h *g,
+                                    const char *appliance,
 				    int flags)
 {
   CLEANUP_FREE_STRINGSBUF DECLARE_STRINGSBUF (argv);
@@ -164,8 +205,12 @@ guestfs_int_appliance_command_line (guestfs_h *g, const char *appliance_dev,
   guestfs_int_add_string (g, &argv, "8250.nr_uarts=1");
 
   /* Tell supermin about the appliance device. */
-  if (appliance_dev)
-    guestfs_int_add_sprintf (g, &argv, "root=%s", appliance_dev);
+  if (appliance) {
+    CLEANUP_FREE char *uuid = get_root_uuid (g, appliance);
+    if (!uuid)
+      return NULL;
+    guestfs_int_add_sprintf (g, &argv, "root=UUID=%s", uuid);
+  }
 
   /* SELinux - deprecated setting, never worked and should not be enabled. */
   if (g->selinux)

lib/guestfs-internal.h

@@ -688,7 +688,7 @@ extern int guestfs_int_build_appliance (guestfs_h *g, char **kernel, char **init
 const char *guestfs_int_get_cpu_model (int kvm);
 
 /* appliance-kcmdline.c */
-extern char *guestfs_int_appliance_command_line (guestfs_h *g, const char *appliance_dev, int flags);
+extern char *guestfs_int_appliance_command_line (guestfs_h *g, const char *appliance, int flags);
 #define APPLIANCE_COMMAND_LINE_IS_TCG 1
 
 /* appliance-uefi.c */

lib/launch-direct.c

@@ -61,8 +61,6 @@ struct backend_direct_data {
   char guestfsd_sock[UNIX_PATH_MAX]; /* Path to daemon socket. */
 };
 
-static char *make_appliance_dev (guestfs_h *g);
-
 static char *
 create_cow_overlay_direct (guestfs_h *g, void *datav, struct drive *drv)
 {
@@ -382,7 +380,6 @@ launch_direct (guestfs_h *g, void *datav, const char *arg)
   int uefi_flags;
   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;
   struct hv_param *hp;
@@ -636,8 +633,6 @@ launch_direct (guestfs_h *g, void *datav, const char *arg)
       append_list ("scsi-hd");
       append_list ("drive=appliance");
     } end_list ();
-
-    appliance_dev = make_appliance_dev (g);
   }
 
   /* Create the virtio serial bus. */
@@ -697,7 +692,7 @@ launch_direct (guestfs_h *g, void *datav, const char *arg)
   flags = 0;
   if (!has_kvm || force_tcg)
     flags |= APPLIANCE_COMMAND_LINE_IS_TCG;
-  append = guestfs_int_appliance_command_line (g, appliance_dev, flags);
+  append = guestfs_int_appliance_command_line (g, appliance, flags);
   arg ("-append", append);
 
   /* Note: custom command line parameters must come last so that
@@ -961,33 +956,6 @@ launch_direct (guestfs_h *g, void *datav, 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)
-{
-  size_t i, index = 0;
-  struct drive *drv;
-  char dev[64] = "/dev/sd";
-
-  /* Calculate the index of the drive. */
-  ITER_DRIVES (g, i, drv) {
-    if (drv->iface == NULL || STREQ (drv->iface, "ide"))
-      index++;
-  }
-
-  guestfs_int_drive_name (index, &dev[7]);
-
-  return safe_strdup (g, dev);  /* Caller frees. */
-}
-
 static int
 shutdown_direct (guestfs_h *g, void *datav, int check_for_errors)
 {

lib/launch-libvirt.c

@@ -153,8 +153,9 @@ struct backend_libvirt_data {
  */
 struct libvirt_xml_params {
   struct backend_libvirt_data *data;
-  char *kernel;                 /* paths to kernel and initrd */
+  char *kernel;                 /* paths to kernel, initrd and appliance */
   char *initrd;
+  char *appliance;
   char *appliance_overlay;      /* path to qcow2 overlay backed by appliance */
   char appliance_dev[64];       /* appliance device name */
   size_t appliance_index;       /* index of appliance */
@@ -323,10 +324,10 @@ launch_libvirt (guestfs_h *g, void *datav, const char *libvirt_uri)
     .data = data,
     .kernel = NULL,
     .initrd = NULL,
+    .appliance = NULL,
     .appliance_overlay = NULL,
   };
   CLEANUP_FREE xmlChar *xml = NULL;
-  CLEANUP_FREE char *appliance = NULL;
   struct sockaddr_un addr;
   struct drive *drv;
   size_t i;
@@ -486,18 +487,18 @@ launch_libvirt (guestfs_h *g, void *datav, const char *libvirt_uri)
   debug (g, "build appliance");
 
   if (guestfs_int_build_appliance (g, &params.kernel, &params.initrd,
-                                   &appliance) == -1)
+                                   &params.appliance) == -1)
     goto cleanup;
 
   guestfs_int_launch_send_progress (g, 3);
   TRACE0 (launch_build_libvirt_appliance_end);
 
   /* Note that appliance can be NULL if using the old-style appliance. */
-  if (appliance) {
+  if (params.appliance) {
 #ifndef APPLIANCE_FORMAT_AUTO
-    params.appliance_overlay = make_qcow2_overlay (g, appliance, "raw");
+    params.appliance_overlay = make_qcow2_overlay (g, params.appliance, "raw");
 #else
-    params.appliance_overlay = make_qcow2_overlay (g, appliance, NULL);
+    params.appliance_overlay = make_qcow2_overlay (g, params.appliance, NULL);
 #endif
     if (!params.appliance_overlay)
       goto cleanup;
@@ -714,7 +715,7 @@ launch_libvirt (guestfs_h *g, void *datav, const char *libvirt_uri)
     goto cleanup;
   }
 
-  if (appliance)
+  if (params.appliance)
     guestfs_int_add_dummy_appliance_drive (g);
 
   TRACE0 (launch_libvirt_end);
@@ -726,6 +727,7 @@ launch_libvirt (guestfs_h *g, void *datav, const char *libvirt_uri)
 
   free (params.kernel);
   free (params.initrd);
+  free (params.appliance);
   free (params.appliance_overlay);
 
   return 0;
@@ -751,6 +753,7 @@ launch_libvirt (guestfs_h *g, void *datav, const char *libvirt_uri)
 
   free (params.kernel);
   free (params.initrd);
+  free (params.appliance);
   free (params.appliance_overlay);
 
   g->state = CONFIG;
@@ -1216,7 +1219,7 @@ construct_libvirt_xml_boot (guestfs_h *g,
   flags = 0;
   if (!params->data->is_kvm)
     flags |= APPLIANCE_COMMAND_LINE_IS_TCG;
-  cmdline = guestfs_int_appliance_command_line (g, params->appliance_dev, flags);
+  cmdline = guestfs_int_appliance_command_line (g, params->appliance, flags);
 
   start_element ("os") {
     if (params->data->firmware)

m4/guestfs-appliance.m4

@@ -34,7 +34,8 @@ then you have to --disable-appliance as well, since the appliance contains
 the daemon inside it.])
 fi
 
-dnl Check for supermin >= 5.1.0.
+dnl Check for supermin >= 5.1.18.
+dnl We don't check it, but it must support the root=UUID=... notation.
 AC_PATH_PROG([SUPERMIN],[supermin],[no])
 
 dnl Pass supermin --packager-config option.