Re: [PATCH v4] log: respect rte_openlog_stream calls before rte_eal_init

[John Ousterhout <ouster@cs.stanford.edu>]

Suppose an application starts up, calls rte_eal_init, then later on invokes
code like this:

fclose(stderr);
stderr = fopen("foo", "w");

This might happen if it is using stderr for its log, but decides to roll
the log over to a new file.

Now stderr has changed.  However, if DPDK made a copy of it with a
statement like this:

FILE *default_log_stream = stderr;

then default_log_stream will continue to refer to the old log file, not the
new one.

Thus, it's better to grab the value of stderr at the last possible moment
before logging.

-John-

On Wed, Oct 12, 2016 at 12:47 PM, Thomas Monjalon <thomas.monjalon@6wind.com
> wrote:

> 2016-10-12 12:38, John Ousterhout:
> > @@ -127,6 +125,19 @@ rte_vlog(uint32_t level, uint32_t logtype, const
> char *format, va_list ap)
> >  {
> >       int ret;
> >       FILE *f = rte_logs.file;
> > +     if (f == NULL) {
> > +             f = default_log_stream;
> > +             if (f == NULL) {
> > +                     /*
> > +                      * Grab the current value of stderr here, rather
> than
> > +                      * just initializing default_log_stream to stderr.
> This
> > +                      * ensures that we will always use the current
> value
> > +                      * of stderr, even if the application closes and
> > +                      * reopens it.
> > +                      */
> > +                     f = stderr;
> > +             }
> > +     }
>
> I don't understand this big comment.
> What is the difference with initializing default_log_stream to stderr?
> What do you mean by "if the application closes and reopens it"?
>