Re: [PATCH 2/2] tools/xl: Allow specifying JSON for domain configuration file format

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Tue, Apr 19, 2022 at 06:23:41PM -0700, Elliott Mitchell wrote:
> JSON is currently used when saving domains to mass storage.  Being able
> to use JSON as the normal input to `xl create` has potential to be
> valuable.  Add the functionality.

"potential", right, but it isn't hasn't been really tested. When
implemented, I think the intend of the json format was for libxl to
communicate with itself while migrating a guest (or save/restore). It
would be nice to know if it actually can work.

> Signed-off-by: Elliott Mitchell <ehem+xen@xxxxxxx>
> ---
> diff --git a/tools/xl/xl.h b/tools/xl/xl.h
> index c5c4bedbdd..a0c03f96df 100644
> --- a/tools/xl/xl.h
> +++ b/tools/xl/xl.h
> @@ -49,6 +49,11 @@ struct domain_create {
>      int migrate_fd; /* -1 means none */
>      int send_back_fd; /* -1 means none */
>      char **migration_domname_r; /* from malloc */
> +    enum {
> +        FORMAT_DEFAULT,
> +        FORMAT_JSON,
> +        FORMAT_LEGACY,
> +    } format;

I think the name "format" here is too generic, we are in the struct
"domain_create" and this new format field isn't intended to specify the
format of the domain. I think "config_file_format" would be better, as
it is only used for the format of the config_file.

Also I don't think having "_DEFAULT" would be useful, we need to know
what the format is intended to be before starting to parse the file, and
I don't think changing the default is going to work. So for the enum, we
could have "_LEGACY = 0".

The prefix "FORMAT_" feels a bit generic, maybe "CONFIG_FORMAT_" would
be better, or something else.

>  };
>  
>  int create_domain(struct domain_create *dom_info);
> diff --git a/tools/xl/xl_cmdtable.c b/tools/xl/xl_cmdtable.c
> index f546beaceb..04d579a596 100644
> --- a/tools/xl/xl_cmdtable.c
> +++ b/tools/xl/xl_cmdtable.c
> @@ -31,6 +31,8 @@ const struct cmd_spec cmd_table[] = {
>        "-h                      Print this help.\n"
>        "-p                      Leave the domain paused after it is 
> created.\n"
>        "-f FILE, --defconfig=FILE\n                     Use the given 
> configuration file.\n"
> +      "-j, --json              Interpret configuration file as JSON format\n"
> +      "-J                      Use traditional configuration file format 
> (current default)\n"

I don't think this new "-J" option would be useful, just the "-j" should be
enough.

>        "-n, --dryrun            Dry run - prints the resulting 
> configuration\n"
>        "                         (deprecated in favour of global -N 
> option).\n"
>        "-q, --quiet             Quiet.\n"
> diff --git a/tools/xl/xl_vmcontrol.c b/tools/xl/xl_vmcontrol.c
> index 2ec4140258..41bd919d1d 100644
> --- a/tools/xl/xl_vmcontrol.c
> +++ b/tools/xl/xl_vmcontrol.c
> @@ -789,7 +789,7 @@ int create_domain(struct domain_create *dom_info)
>                  extra_config);
>          }
>          config_source=config_file;
> -        config_in_json = false;
> +        config_in_json = dom_info.format == FORMAT_JSON ? true : false;

This doesn't build, "dom_info" is a pointer.

Also, "? true : false;" is weird in C.


>      } else {
>          if (!config_data) {
>              fprintf(stderr, "Config file not specified and"
> @@ -1173,6 +1173,7 @@ int main_create(int argc, char **argv)
>          {"defconfig", 1, 0, 'f'},
>          {"dryrun", 0, 0, 'n'},
>          {"ignore-global-affinity-masks", 0, 0, 'i'},
> +        {"json", 0, 0, 'j'},
>          {"quiet", 0, 0, 'q'},
>          {"vncviewer", 0, 0, 'V'},
>          {"vncviewer-autopass", 0, 0, 'A'},
> @@ -1181,18 +1182,23 @@ int main_create(int argc, char **argv)
>  
>      dom_info.extra_config = NULL;
>  
> +    dom_info.format = FORMAT_DEFAULT;
> +
>      if (argv[1] && argv[1][0] != '-' && !strchr(argv[1], '=')) {
>          filename = argv[1];
>          argc--; argv++;
>      }
>  
> -    SWITCH_FOREACH_OPT(opt, "Ffnq:AVcdeip", opts, "create", 0) {
> +    SWITCH_FOREACH_OPT(opt, "FJfjnq:AVcdeip", opts, "create", 0) {
>      case 'A':
>          vnc = vncautopass = 1;
>          break;
>      case 'F':
>          daemonize = 0;
>          break;
> +    case 'J':
> +        dom_info.format = FORMAT_LEGACY;
> +        break;
>      case 'V':
>          vnc = 1;
>          break;
> @@ -1212,6 +1218,9 @@ int main_create(int argc, char **argv)
>      case 'i':
>          ignore_masks = 1;
>          break;
> +    case 'j':
> +        dom_info.format = FORMAT_JSON;

This setting is ignored, as "dom_info" is reset later.

> +        break;
>      case 'n':
>          dryrun_only = 1;
>          break;

Thanks,

-- 
Anthony PERARD