Add two functions to print an error/warning report once depending
on a passed-in condition variable and flip it if printed. This is
useful if you want to print a message not once-globally, but e.g.
once-per-device.

Inspired by warn_once() in hw/vfio/ccw.c.

Signed-off-by: Cornelia Huck <cohuck@redhat.com>
---
 include/qemu/error-report.h |  5 +++++
 util/qemu-error.c           | 44 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/include/qemu/error-report.h b/include/qemu/error-report.h
index 72fab2b031..d2a6515e68 100644
--- a/include/qemu/error-report.h
+++ b/include/qemu/error-report.h
@@ -44,6 +44,11 @@ void error_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
 void warn_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
 void info_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
 
+void error_report_once_cond(bool *printed, const char *fmt, ...)
+    GCC_FMT_ATTR(2, 3);
+void warn_report_once_cond(bool *printed, const char *fmt, ...)
+    GCC_FMT_ATTR(2, 3);
+
 /*
  * Similar to error_report(), except it prints the message just once.
  * Return true when it prints, false otherwise.
diff --git a/util/qemu-error.c b/util/qemu-error.c
index a25d3b94c6..0894ab6995 100644
--- a/util/qemu-error.c
+++ b/util/qemu-error.c
@@ -310,3 +310,47 @@ void info_report(const char *fmt, ...)
     vreport(REPORT_TYPE_INFO, fmt, ap);
     va_end(ap);
 }
+
+/*
+ * If *printed is false, print an error message to current monitor if we
+ * have one, else to stderr, and flip *printed to true.
+ * If printed is NULL, do not print anything.
+ * Format arguments like sprintf().  The resulting message should be
+ * a single phrase, with no newline or trailing punctuation.
+ * Prepend the current location and append a newline.
+ * It's wrong to call this in a QMP monitor.  Use error_setg() there.
+ */
+void error_report_once_cond(bool *printed, const char *fmt, ...)
+{
+    va_list ap;
+
+    if (!printed || *printed) {
+        return;
+    }
+    *printed = true;
+    va_start(ap, fmt);
+    vreport(REPORT_TYPE_ERROR, fmt, ap);
+    va_end(ap);
+}
+
+/*
+ * If *printed is false, print a warning message to current monitor if we
+ * have one, else to stderr, and flip *printed to true.
+ * If printed is NULL, do not print anything.
+ * Format arguments like sprintf().  The resulting message should be
+ * a single phrase, with no newline or trailing punctuation.
+ * Prepend the current location and append a newline.
+ * It's wrong to call this in a QMP monitor.  Use error_setg() there.
+ */
+void warn_report_once_cond(bool *printed, const char *fmt, ...)
+{
+    va_list ap;
+
+    if (!printed || *printed) {
+        return;
+    }
+    *printed = true;
+    va_start(ap, fmt);
+    vreport(REPORT_TYPE_WARNING, fmt, ap);
+    va_end(ap);
+}
-- 
2.14.4

Cornelia Huck <cohuck@redhat.com> writes:

> Add two functions to print an error/warning report once depending
> on a passed-in condition variable and flip it if printed. This is
> useful if you want to print a message not once-globally, but e.g.
> once-per-device.
>
> Inspired by warn_once() in hw/vfio/ccw.c.

This leaves the reader wondering why you don't replace that function.
You do, in PATCH 3.  I'd either announce that here, or squash the two
patches.

>
> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> ---
>  include/qemu/error-report.h |  5 +++++
>  util/qemu-error.c           | 44 ++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 49 insertions(+)
>
> diff --git a/include/qemu/error-report.h b/include/qemu/error-report.h
> index 72fab2b031..d2a6515e68 100644
> --- a/include/qemu/error-report.h
> +++ b/include/qemu/error-report.h
> @@ -44,6 +44,11 @@ void error_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
>  void warn_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
>  void info_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
>  
> +void error_report_once_cond(bool *printed, const char *fmt, ...)
> +    GCC_FMT_ATTR(2, 3);
> +void warn_report_once_cond(bool *printed, const char *fmt, ...)
> +    GCC_FMT_ATTR(2, 3);
> +
>  /*
>   * Similar to error_report(), except it prints the message just once.
>   * Return true when it prints, false otherwise.
> diff --git a/util/qemu-error.c b/util/qemu-error.c
> index a25d3b94c6..0894ab6995 100644
> --- a/util/qemu-error.c
> +++ b/util/qemu-error.c
> @@ -310,3 +310,47 @@ void info_report(const char *fmt, ...)
>      vreport(REPORT_TYPE_INFO, fmt, ap);
>      va_end(ap);
>  }
> +
> +/*
> + * If *printed is false, print an error message to current monitor if we
> + * have one, else to stderr, and flip *printed to true.
> + * If printed is NULL, do not print anything.

Any particular reason for supporting null @printed?

For what it's worth, warn_once() supports it, but its caller doesn't use
it.

> + * Format arguments like sprintf().  The resulting message should be
> + * a single phrase, with no newline or trailing punctuation.
> + * Prepend the current location and append a newline.
> + * It's wrong to call this in a QMP monitor.  Use error_setg() there.
> + */
> +void error_report_once_cond(bool *printed, const char *fmt, ...)
> +{
> +    va_list ap;
> +
> +    if (!printed || *printed) {
> +        return;
> +    }
> +    *printed = true;
> +    va_start(ap, fmt);
> +    vreport(REPORT_TYPE_ERROR, fmt, ap);
> +    va_end(ap);
> +}
> +
> +/*
> + * If *printed is false, print a warning message to current monitor if we
> + * have one, else to stderr, and flip *printed to true.
> + * If printed is NULL, do not print anything.
> + * Format arguments like sprintf().  The resulting message should be
> + * a single phrase, with no newline or trailing punctuation.
> + * Prepend the current location and append a newline.
> + * It's wrong to call this in a QMP monitor.  Use error_setg() there.
> + */
> +void warn_report_once_cond(bool *printed, const char *fmt, ...)
> +{
> +    va_list ap;
> +
> +    if (!printed || *printed) {
> +        return;
> +    }
> +    *printed = true;
> +    va_start(ap, fmt);
> +    vreport(REPORT_TYPE_WARNING, fmt, ap);
> +    va_end(ap);
> +}

On Wed, 29 Aug 2018 18:07:46 +0200
Markus Armbruster <armbru@redhat.com> wrote:

> Cornelia Huck <cohuck@redhat.com> writes:
> 
> > Add two functions to print an error/warning report once depending
> > on a passed-in condition variable and flip it if printed. This is
> > useful if you want to print a message not once-globally, but e.g.
> > once-per-device.
> >
> > Inspired by warn_once() in hw/vfio/ccw.c.  
> 
> This leaves the reader wondering why you don't replace that function.
> You do, in PATCH 3.  I'd either announce that here, or squash the two
> patches.

Squashing probably makes the most sense.

> 
> >
> > Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> > ---
> >  include/qemu/error-report.h |  5 +++++
> >  util/qemu-error.c           | 44 ++++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 49 insertions(+)
> >
> > diff --git a/include/qemu/error-report.h b/include/qemu/error-report.h
> > index 72fab2b031..d2a6515e68 100644
> > --- a/include/qemu/error-report.h
> > +++ b/include/qemu/error-report.h
> > @@ -44,6 +44,11 @@ void error_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
> >  void warn_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
> >  void info_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
> >  
> > +void error_report_once_cond(bool *printed, const char *fmt, ...)
> > +    GCC_FMT_ATTR(2, 3);
> > +void warn_report_once_cond(bool *printed, const char *fmt, ...)
> > +    GCC_FMT_ATTR(2, 3);
> > +
> >  /*
> >   * Similar to error_report(), except it prints the message just once.
> >   * Return true when it prints, false otherwise.
> > diff --git a/util/qemu-error.c b/util/qemu-error.c
> > index a25d3b94c6..0894ab6995 100644
> > --- a/util/qemu-error.c
> > +++ b/util/qemu-error.c
> > @@ -310,3 +310,47 @@ void info_report(const char *fmt, ...)
> >      vreport(REPORT_TYPE_INFO, fmt, ap);
> >      va_end(ap);
> >  }
> > +
> > +/*
> > + * If *printed is false, print an error message to current monitor if we
> > + * have one, else to stderr, and flip *printed to true.
> > + * If printed is NULL, do not print anything.  
> 
> Any particular reason for supporting null @printed?
> 
> For what it's worth, warn_once() supports it, but its caller doesn't use
> it.

I can change this to asserting on NULL @printed. If you call this with
NULL, you probably have messed up somewhere already.

> 
> > + * Format arguments like sprintf().  The resulting message should be
> > + * a single phrase, with no newline or trailing punctuation.
> > + * Prepend the current location and append a newline.
> > + * It's wrong to call this in a QMP monitor.  Use error_setg() there.
> > + */
> > +void error_report_once_cond(bool *printed, const char *fmt, ...)
> > +{
> > +    va_list ap;
> > +
> > +    if (!printed || *printed) {
> > +        return;
> > +    }
> > +    *printed = true;
> > +    va_start(ap, fmt);
> > +    vreport(REPORT_TYPE_ERROR, fmt, ap);
> > +    va_end(ap);
> > +}
> > +
> > +/*
> > + * If *printed is false, print a warning message to current monitor if we
> > + * have one, else to stderr, and flip *printed to true.
> > + * If printed is NULL, do not print anything.
> > + * Format arguments like sprintf().  The resulting message should be
> > + * a single phrase, with no newline or trailing punctuation.
> > + * Prepend the current location and append a newline.
> > + * It's wrong to call this in a QMP monitor.  Use error_setg() there.
> > + */
> > +void warn_report_once_cond(bool *printed, const char *fmt, ...)
> > +{
> > +    va_list ap;
> > +
> > +    if (!printed || *printed) {
> > +        return;
> > +    }
> > +    *printed = true;
> > +    va_start(ap, fmt);
> > +    vreport(REPORT_TYPE_WARNING, fmt, ap);
> > +    va_end(ap);
> > +}