Re: [PATCH 04/28] qemu-img: global option processing and error printing

["Daniel P. Berrangé" <berrange@redhat.com>]

On Thu, Feb 22, 2024 at 12:15:45AM +0300, Michael Tokarev wrote:
> In order to correctly print executable name in various
> error messages, pass argv[0] to error_exit() function.
> This way, error messages will refer to actual executable
> name, which may be different from 'qemu-img'.
> 
> For subcommands, pass whole argv[] array, so argv[0] is
> the executable name, not subcommand name.  In order to
> do that, avoid resetting optind but continue with the
> next option.  Also don't require at least 3 options on
> the command line: it makes no sense with options before
> subcommand.
> 
> Before invoking a subcommand, replace argv[0] to include
> the subcommand name.
> 
> Introduce tryhelp() function which just prints
> 
>  try 'command-name --help' for more info
> 
> and exits.  When tryhelp() is called from within a subcommand
> handler, the message will look like:
> 
>  try 'command-name subcommand --help' for more info
> 
> qemu-img uses getopt_long() with ':' as the first char in
> optstring parameter, which means it doesn't print error
> messages but return ':' or '?' instead, and qemu-img uses
> unrecognized_option() or missing_argument() function to
> print error messages.  But it doesn't quite work:
> 
>  $ ./qemu-img -xx
>  qemu-img: unrecognized option './qemu-img'
> 
> so the aim is to let getopt_long() to print regular error
> messages instead (removing ':' prefix from optstring) and
> remove handling of '?' and ':' "options" entirely.  With
> concatenated argv[0] and the subcommand, it all finally
> does the right thing in all cases.  This will be done in
> subsequent changes command by command, with main() done
> last.
> 
> unrecognized_option() and missing_argument() functions
> prototypes aren't changed by this patch, since they're
> called from many places and will be removed a few patches
> later.  Only artifical "qemu-img" argv0 is provided in
> there for now.
> 
> Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
> ---
>  qemu-img.c | 75 +++++++++++++++++++++++++++---------------------------
>  1 file changed, 38 insertions(+), 37 deletions(-)
> @@ -5602,10 +5602,11 @@ int main(int argc, char **argv)
>      /* find the command */
>      for (cmd = img_cmds; cmd->name != NULL; cmd++) {
>          if (!strcmp(cmdname, cmd->name)) {
> +            argv[0] = g_strdup_printf("%s %s", argv[0], cmdname);
>              return cmd->handler(argc, argv);

This is going to result in valgrind warning that argv[0] is leaked.

How about:

  g_autofree char *cmdargv0 = g_strdup_printf("%s %s", argv[0], cmdname);
  argv[0] = cmdargv0;
  return cmd->handler(argc, argv);

>          }
>      }
>  
>      /* not found */
> -    error_exit("Command not found: %s", cmdname);
> +    error_exit(argv[0], "Command not found: %s", cmdname);
>  }
> -- 
> 2.39.2
> 
> 

With regards,
Daniel
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