[Libguestfs] [PATCH v3] appliance: extract UUID from QCOW2 disk image

[Andrey Shinkevich]

For the appliance of the QCOW2 format, the function get_root_uuid()
fails to get the UUID of the disk image.
In this case, let us read the first 256k bytes of the disk image  with
the 'qemu-img dd' command. Then pass the read block to the 'file'
command.

Suggested-by: Denis V. Lunev <den at openvz.org>
Signed-off-by: Andrey Shinkevich <andrey.shinkevich at virtuozzo.com>
---
v3:
  01: The code refactoring was made based on reviewers comments.
      The e-mail thread Message-Id:
      <1597246570-901723-1-git-send-email-andrey.shinkevich at virtuozzo.com>

 lib/appliance-kcmdline.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 67 insertions(+), 1 deletion(-)

diff --git a/lib/appliance-kcmdline.c b/lib/appliance-kcmdline.c
index fbeb4f4..e088fc0 100644
--- a/lib/appliance-kcmdline.c
+++ b/lib/appliance-kcmdline.c
@@ -71,7 +71,7 @@ read_uuid (guestfs_h *g, void *retv, const char *line, size_t len)
  * The L<file(1)> command does the hard work.
  */
 static char *
-get_root_uuid (guestfs_h *g, const char *appliance)
+get_root_uuid_with_file (guestfs_h *g, const char *appliance)
 {
   CLEANUP_CMD_CLOSE struct command *cmd = guestfs_int_new_command (g);
   char *ret = NULL;
@@ -96,6 +96,72 @@ get_root_uuid (guestfs_h *g, const char *appliance)
 }
 
 /**
+ * Read the first 256k bytes of the in_file with L<qemu-img(1)> command
+ * and write them into the out_file. That may be useful to get UUID of
+ * the QCOW2 disk image with further L<file(1)> command.
+ * The function returns zero if successful, otherwise -1.
+ */
+static int
+run_qemu_img_dd (guestfs_h *g, const char *in_file, char *out_file)
+{
+  CLEANUP_CMD_CLOSE struct command *cmd = guestfs_int_new_command (g);
+  int r;
+
+  guestfs_int_cmd_add_arg (cmd, "qemu-img");
+  guestfs_int_cmd_add_arg (cmd, "dd");
+  guestfs_int_cmd_add_arg_format (cmd, "if=%s", in_file);
+  guestfs_int_cmd_add_arg_format (cmd, "of=%s", out_file);
+  guestfs_int_cmd_add_arg (cmd, "bs=256k");
+  guestfs_int_cmd_add_arg (cmd, "count=1");
+
+  r = guestfs_int_cmd_run (cmd);
+  if (r == -1) {
+    error (g, "Failed to run qemu-img");
+    return -1;
+  }
+  if (!WIFEXITED (r) || WEXITSTATUS (r) != 0) {
+    guestfs_int_external_command_failed (g, r, "qemu-img dd", NULL);
+    return -1;
+  }
+
+  return 0;
+}
+
+/**
+ * Get the UUID from the appliance disk image.
+ */
+static char *
+get_root_uuid (guestfs_h *g, const char *appliance)
+{
+  char *uuid = NULL;
+  int ret;
+  CLEANUP_UNLINK_FREE char *tmpfile = NULL;
+
+  uuid = get_root_uuid_with_file (g, appliance);
+  if (uuid) {
+      return uuid;
+  }
+
+  tmpfile = guestfs_int_make_temp_path (g, "root", "raw");
+  if (!tmpfile) {
+    error (g, "get_root_uuid: failed to make temporary file");
+    return NULL;
+  }
+
+  ret = run_qemu_img_dd (g, appliance, tmpfile);
+  if (ret < 0) {
+    return NULL;
+  }
+
+  uuid = get_root_uuid_with_file (g, tmpfile);
+  if (!uuid) {
+    error (g, "Failed to get the appliance UUID");
+  }
+
+  return uuid;
+}
+
+/**
  * 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
-- 
1.8.3.1