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

12.08.2020 15:52, Vladimir Sementsov-Ogievskiy wrote: >12.08.2020 15:39, Andrey Shinkevich wrote: >>For the appliance of the QCOW2 format, get the UUID of the disk by >>reading the first 256k bytes with 'qemu-img dd' command. Then pass the >>read block to the 'file' command. In case of failure, run the 'file' >>command again directly. >> >>Suggested-by: Denis V. Lunev <den(a)openvz.org&gt; >>Signed-off-by: Andrey Shinkevich <andrey.shinkevich(a)virtuozzo.com&gt; >>--- >>  lib/appliance-kcmdline.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++- >>  1 file changed, 69 insertions(+), 1 deletion(-) >> >>diff --git a/lib/appliance-kcmdline.c b/lib/appliance-kcmdline.c >>index 211cc46..3bb8bcd 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) >>+do_get_root_uuid (guestfs_h *g, const char *appliance) >>  { >>    CLEANUP_CMD_CLOSE struct command *cmd = guestfs_int_new_command (g); >>    char *ret = NULL; >>@@ -96,6 +96,74 @@ 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; > >Generally, don't use uppercase for local variables, I'd rename it s/UUID/uuid/ > >>+  int ret; >>+  char tmp_file[] = "/tmp/libguestfsXXXXXX"; >>+ >>+  if (!mktemp (tmp_file)) { >>+    error (g, "get_root_uuid: mktemp failed"); >>+    return NULL; > >Hmm, if failed to create temp file, we still can try call do_get_root_uuid on original appliance image. > Another thought: with this patch, in case of raw appliance, we will do copying for nothing. Probably better try file command on original image first, and if failed, try with qemu-img dd.

>>+  } >>+ >>+  ret = run_qemu_img_dd (g, appliance, tmp_file); >>+  if (ret == 0) { >>+    UUID = do_get_root_uuid (g, tmp_file); >>+    if (UUID) { >>+      goto out; >>+    } >>+  } >>+ >>+  /* We get here in case of failure to extract a UUID from the temporary file. >>+   * Let us try to get the UUID from the appliance directly. >>+   */ >>+  UUID = do_get_root_uuid (g, appliance); >>+  if (!UUID) { >>+    error (g, "Failed to get the appliance UUID"); >>+  } >>+ >>+out: >>+  unlink (tmp_file); >>+  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 >> > > -- Best regards, Vladimir