Libguestfs - Aug 2020 - Re: [PATCH] appliance: extract UUID from QCOW2 disk image

On Wed, Aug 12, 2020 at 03:52:34PM +0300, 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@openvz.org>
> >Signed-off-by: Andrey Shinkevich
<andrey.shinkevich@virtuozzo.com>
> >---
> >  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.
This is related to the only issue I had with this patch.  Can
we run the find command first on the original appliance, and only
if it fails take the slower qemu-img dd patch?

I tested this patch as it is, and it worked for me.

Rich.
> >+  }
> >+
> >+  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
-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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