Re: [Qemu-devel] [PATCH v2 05/23] error: Improve documentation around error_append_hint()

[Eric Blake <eblake@redhat.com>]

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On 12/17/2015 09:49 AM, Markus Armbruster wrote:
> While there, tighten its assertion.
> 
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---
>  include/qapi/error.h | 19 +++++++++++++++++--
>  util/error.c         |  2 +-
>  2 files changed, 18 insertions(+), 3 deletions(-)
> 
> diff --git a/include/qapi/error.h b/include/qapi/error.h
> index b2362a5..048d947 100644
> --- a/include/qapi/error.h
> +++ b/include/qapi/error.h
> @@ -18,6 +18,15 @@
>   * Create an error:
>   *     error_setg(&err, "situation normal, all fouled up");
>   *
> + * Create an error and add additional explanation:
> + *     error_setg(&err, "invalid quark");
> + *     error_append_hint(&err, "Valid quarks are up, down, strange, "
> + *                       "charm, top, bottom\n");

Do we want to allow/encourage a trailing dot in the hint?  I'm fine if
we don't - but once we document its usage, we should probably then be
consistent with what we document; qemu-option.c used a trailing dot,
qdev-monitor.c did not.

> + *
> + * Do *not* contract this to
> + *     error_setg(&err, "invalid quark\n"
> + *                "Valid quarks are up, down, strange, charm, top, bottom");
> + *
>   * Report an error to stderr:
>   *     error_report_err(err);
>   * This frees the error object.
> @@ -26,6 +35,7 @@
>   *     const char *msg = error_get_pretty(err);
>   *     do with msg what needs to be done...
>   *     error_free(err);
> + * Note that this loses hints added with error_append_hint().
>   *
>   * Handle an error without reporting it (just for completeness):
>   *     error_free(err);
> @@ -128,6 +138,7 @@ ErrorClass error_get_class(const Error *err);
>   * If @errp is anything else, *@errp must be NULL.
>   * The new error's class is ERROR_CLASS_GENERIC_ERROR, and its
>   * human-readable error message is made from printf-style @fmt, ...
> + * The resulting message should not contain newlines.

Should we also discourage trailing punctuation?

Should we also mention no need for leading 'error: ' prefix?

>   */
>  #define error_setg(errp, fmt, ...)                              \
>      error_setg_internal((errp), __FILE__, __LINE__, __func__,   \
> @@ -184,7 +195,11 @@ void error_propagate(Error **dst_errp, Error *local_err);
>  
>  /**
>   * Append a printf-style human-readable explanation to an existing error.
> - * May be called multiple times, and safe if @errp is NULL.
> + * @errp may be NULL, but neither &error_fatal nor &error_abort.

As a native speaker, 'not' sounds better than 'neither' in that
sentence.  But I think both choices are grammatically correct.

> + * Trivially the case if you call it only after error_setg() or
> + * error_propagate().
> + * May be called multiple times.  The resulting hint should end with a
> + * newline.
>   */
>  void error_append_hint(Error **errp, const char *fmt, ...)
>      GCC_FMT_ATTR(2, 3);
> @@ -218,7 +233,7 @@ void error_free_or_abort(Error **errp);
>  /*
>   * Convenience function to error_report() and free @err.
>   */
> -void error_report_err(Error *);
> +void error_report_err(Error *err);
>  
>  /*
>   * Just like error_setg(), except you get to specify the error class.
> diff --git a/util/error.c b/util/error.c
> index 9b27c45..ebfb74b 100644
> --- a/util/error.c
> +++ b/util/error.c
> @@ -132,7 +132,7 @@ void error_append_hint(Error **errp, const char *fmt, ...)
>          return;
>      }
>      err = *errp;
> -    assert(err && errp != &error_abort);
> +    assert(err && errp != &error_abort && errp != &error_fatal);

Otherwise looks reasonable.

>  
>      if (!err->hint) {
>          err->hint = g_string_new(NULL);
> 

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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