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Re: [libvirt] [PATCH] Allow stack traces to be included with log messages



On 05/09/2012 08:22 AM, Daniel P. Berrange wrote:
> From: "Daniel P. Berrange" <berrange redhat com>
> 
> Sometimes it is useful to see the callpath for log messages.
> This change enhances the log filter syntax so that stck traces

s/stck/stack/

> can be show by setting '1:+NAME' instead of '1:NAME'.

Cool.

> * docs/logging.html.in: Document new syntax
> * configure.ac: Check for execinfo.h
> * src/util/logging.c, src/util/logging.h: Add support for
>   stack traces

Of course, this seems to be Linux-only, but still useful.

> +++ b/docs/logging.html.in
> @@ -114,8 +114,10 @@
>      </h3>
>      <p>The syntax for filters and outputs is the same for both types of
>         variables.</p>
> -    <p>The format for a filter is:</p>
> -    <pre>x:name</pre>
> +    <p>The format for a filter is one of:</p>
> +    <pre>
> +  x:name  (log message only)
> +  x:+name (log message + stack trace)</pre>

Does x:+name error out on systems where tracing is not built in, or does
it silently fall back to x:name?

> @@ -538,6 +546,7 @@ static int virLogFiltersCheck(const char *input) {
>      for (i = 0;i < virLogNbFilters;i++) {
>          if (strstr(input, virLogFilters[i].match)) {
>              ret = virLogFilters[i].priority;
> +            *flags =  virLogFilters[i].flags;

Is the double space intentional?

> +
> +static void virLogStackTraceToFd(int fd)
> +{
> +#ifdef HAVE_EXECINFO_H
> +    void *array[100];
> +    int size;
> +
> +#define STRIP_DEPTH 3
> +
> +    size = backtrace(array, sizeof(array)/sizeof(array[0]));

Write the second argument as ARRAY_CARDINALITY(array).

> +    backtrace_symbols_fd(array +  STRIP_DEPTH, size - STRIP_DEPTH, fd);
> +    ignore_value(safewrite(fd, "\n", 1));
> +#else
> +    const char *msg = "stack trace not available on this platform";
> +    ignore_value(safewrite(fd, msg, strlen(msg)));

Is this a one-time error message, printed on first use, or will it
appear on every log message?

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

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