Re: [Qemu-devel] [PATCH] char: don't exit on hmp 'chardev-add help'

[Paolo Bonzini]

On 17/07/2017 12:52, Anton Nefedov wrote:
> qemu_chr_new_from_opts() is used from both vl.c and hmp,
> and it is quite confusing to see qemu suddenly exit after receiving a help
> option in hmp.
> 
> Create a separate function for printing help and let different callers
> react accordingly.
> 
> Signed-off-by: Anton Nefedov <address@hidden>
> ---
>  include/chardev/char.h |  9 +++++++++
>  chardev/char.c         | 27 +++++++++++++++++++--------
>  vl.c                   |  4 ++++
>  3 files changed, 32 insertions(+), 8 deletions(-)
> 
> diff --git a/include/chardev/char.h b/include/chardev/char.h
> index 1604ea9..461962b 100644
> --- a/include/chardev/char.h
> +++ b/include/chardev/char.h
> @@ -59,6 +59,15 @@ struct Chardev {
>  };
>  
>  /**
> + * @qemu_chr_help:
> + *
> + * Print available chardevice backends if 'asked for help' in @opts
> + *
> + * Returns: true if there was a help option
> + */
> +bool qemu_chr_help(QemuOpts *opts);
> +
> +/**
>   * @qemu_chr_new_from_opts:
>   *
>   * Create a new character backend from a QemuOpts list.
> diff --git a/chardev/char.c b/chardev/char.c
> index c34b44a..19833fe 100644
> --- a/chardev/char.c
> +++ b/chardev/char.c
> @@ -604,14 +604,9 @@ ChardevBackend *qemu_chr_parse_opts(QemuOpts *opts, 
> Error **errp)
>      return backend;
>  }
>  
> -Chardev *qemu_chr_new_from_opts(QemuOpts *opts, Error **errp)
> +bool qemu_chr_help(QemuOpts *opts)
>  {
> -    const ChardevClass *cc;
> -    Chardev *chr = NULL;
> -    ChardevBackend *backend = NULL;
> -    const char *name = chardev_alias_translate(qemu_opt_get(opts, 
> "backend"));
> -    const char *id = qemu_opts_id(opts);
> -    char *bid = NULL;
> +    const char *name = qemu_opt_get(opts, "backend");
>  
>      if (name && is_help_option(name)) {
>          GString *str = g_string_new("");
> @@ -620,7 +615,23 @@ Chardev *qemu_chr_new_from_opts(QemuOpts *opts, Error 
> **errp)
>  
>          error_report("Available chardev backend types: %s", str->str);
>          g_string_free(str, true);
> -        exit(0);
> +        return true;
> +    }
> +
> +    return false;
> +}
> +
> +Chardev *qemu_chr_new_from_opts(QemuOpts *opts, Error **errp)
> +{
> +    const ChardevClass *cc;
> +    Chardev *chr = NULL;
> +    ChardevBackend *backend = NULL;
> +    const char *name = chardev_alias_translate(qemu_opt_get(opts, 
> "backend"));
> +    const char *id = qemu_opts_id(opts);
> +    char *bid = NULL;
> +
> +    if (qemu_chr_help(opts)) {
> +        return NULL;
>      }
>  
>      if (id == NULL) {

This is good, if only as a refactoring.

At this point, however, you don't need anymore the qemu_chr_help call below.

Instead, qemu_chr_new_from_opts now has three possible results:

- NULL, no error: help printed

- NULL, error: error

- non-NULL: chardev created

> diff --git a/vl.c b/vl.c
> index fb6b2ef..7cad539 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -2344,6 +2344,10 @@ static int chardev_init_func(void *opaque, QemuOpts 
> *opts, Error **errp)
>  {
>      Error *local_err = NULL;
>  
> +    if (qemu_chr_help(opts)) {
> +        exit(0);
> +    }
> +
>      qemu_chr_new_from_opts(opts, &local_err);

So I think you can instead do:

    if (!qemu_chr_new_from_opts(opts, &local_err)) {
        if (!local_err) {
            exit(0);
        }
        error_report_err(local_err);
        exit(1);
    }

    return 0;

or something like that.

Paolo