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

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.

> +  } > + > +  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 >