[Libguestfs] [PATCH v2] appliance: extract UUID from QCOW2 disk image

[Pino Toscano]

On Wednesday, 12 August 2020 17:36:10 CEST 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 at openvz.org>
> Signed-off-by: Andrey Shinkevich <andrey.shinkevich at virtuozzo.com>
> ---
> v2:
>   01: The order of the function calls to direct <file> command on the appliance
>       and the indirect one (through the temporary file) has been swapped.
> 
>  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 fbeb4f4..c78524b 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)

get_root_uuid_with_file seems a better name, and gives less confusion
than get_root_uuid & do_get_root_uuid.

>  {
>    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;
> +  int ret;
> +  char tmp_file[] = "/tmp/libguestfsXXXXXX";

Please do not hardcode a location, and use the internal temporary
directory instead. The internal guestfs_int_make_temp_path will do
the right job.

Thanks,
-- 
Pino Toscano
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