Re: [PATCH v2 1/9] util/error: Introduce warn_report_once_err()

[Markus Armbruster]

Cédric Le Goater <clg@redhat.com> writes:

> Depending on the configuration, a passthrough device may produce
> recurring DMA mapping errors at runtime and produce a lot of
> output. It is useful to report only once.
>
> Cc: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: Cédric Le Goater <clg@redhat.com>
> ---
>  include/qapi/error.h | 5 +++++
>  util/error.c         | 9 +++++++++
>  2 files changed, 14 insertions(+)
>
> diff --git a/include/qapi/error.h b/include/qapi/error.h
> index 
> 71f8fb2c50eee9a544992d0c05263c9793956fe1..b6ea274882b9788b64d4bb213c3458d7c674a881
>  100644
> --- a/include/qapi/error.h
> +++ b/include/qapi/error.h
> @@ -448,6 +448,11 @@ void error_free_or_abort(Error **errp);
>   */
>  void warn_report_err(Error *err);
>  
> +/*
> + * Convenience function to call warn_report_err() once.
> + */
> +void warn_report_once_err(Error *err);
> +
>  /*
>   * Convenience function to error_report() and free @err.
>   * The report includes hints added with error_append_hint().
> diff --git a/util/error.c b/util/error.c
> index 
> e5e247209a9e0796074a9794f5598325f22f8d35..b8a211cccaa609a93091b86316144a0ad0a02662
>  100644
> --- a/util/error.c
> +++ b/util/error.c
> @@ -247,6 +247,15 @@ void warn_report_err(Error *err)
>      error_free(err);
>  }
>  
> +void warn_report_once_err(Error *err)
> +{
> +        static bool print_once_;
> +        if (!print_once_) {
> +            warn_report_err(err);
> +            print_once_ = true;
> +        }
> +}

Any particular reason for the trailing _ in @print_once_?

The first warning suppresses all subsequent warnings, even if they're
completely different.  PATCH 5 uses this to emit a (rather cryptic)
warning about unexpected mappings once.  If we later add another use
elsewhere, these uses will suppress each other.  Is this what we want?

The related function warn_report_once_cond() takes the flag as a
parameter.  Only the calls using the same flag suppress each other.

> +
>  void error_reportf_err(Error *err, const char *fmt, ...)
>  {
>      va_list ap;