Re: [PATCH v4] testpmd: cleanup cleanly from signal

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 9 Nov 2022 22:46:55 +0100
Mattias Rönnblom <hofors@lysator.liu.se> wrote:

> On 2022-11-09 05:10, Stephen Hemminger wrote:
> > Do a clean shutdown of testpmd when a signal is received;
> > instead of having testpmd kill itself.
> > This fixes problem where a signal could be received
> > in the middle of a PMD and then the signal handler would call
> > PMD's close routine which could cause a deadlock.
> > 
> > Added benefit is it gets rid of Windows specific code.
> > 
> > Fixes: d9a191a00e81 ("app/testpmd: fix quitting in container")
> > Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> > ---
> > v4 - use select() because that is available on Windows; and other
> >       functions poll() and sigaction() are not.
> > 
> >   app/test-pmd/testpmd.c | 63 +++++++++++++++++++++++-------------------
> >   1 file changed, 34 insertions(+), 29 deletions(-)
> > 
> > diff --git a/app/test-pmd/testpmd.c b/app/test-pmd/testpmd.c
> > index cf5942d0c422..274e96cac2d4 100644
> > --- a/app/test-pmd/testpmd.c
> > +++ b/app/test-pmd/testpmd.c
> > @@ -12,6 +12,7 @@
> >   #ifndef RTE_EXEC_ENV_WINDOWS
> >   #include <sys/mman.h>
> >   #endif
> > +#include <sys/select.h>
> >   #include <sys/types.h>
> >   #include <errno.h>
> >   #include <stdbool.h>
> > @@ -4251,26 +4252,11 @@ print_stats(void)
> >   static void
> >   signal_handler(int signum)
> >   {
> > -	if (signum == SIGINT || signum == SIGTERM) {
> > -		fprintf(stderr, "\nSignal %d received, preparing to exit...\n",
> > -			signum);
> > -#ifdef RTE_LIB_PDUMP
> > -		/* uninitialize packet capture framework */
> > -		rte_pdump_uninit();
> > -#endif
> > -#ifdef RTE_LIB_LATENCYSTATS
> > -		if (latencystats_enabled != 0)
> > -			rte_latencystats_uninit();
> > -#endif
> > -		force_quit();
> > -		/* Set flag to indicate the force termination. */
> > -		f_quit = 1;
> > -		/* exit with the expected status */
> > -#ifndef RTE_EXEC_ENV_WINDOWS
> > -		signal(signum, SIG_DFL);
> > -		kill(getpid(), signum);
> > -#endif
> > -	}
> > +	fprintf(stderr, "\nSignal %d %s received, preparing to exit...\n",
> > +		signum, strsignal(signum));  
> 
> fprintf() is not async signal safe, and neither is strsignal().
> 
> This is not a regression introduced by this patch, but I thought it 
> might be worth fixing.
> 
> > +
> > +	/* Set flag to indicate the force termination. */
> > +	f_quit = 1;
> >   }
> >   
> >   int
> > @@ -4449,9 +4435,6 @@ main(int argc, char** argv)
> >   	} else
> >   #endif
> >   	{
> > -		char c;
> > -		int rc;
> > -
> >   		f_quit = 0;
> >   
> >   		printf("No commandline core given, start packet forwarding\n");
> > @@ -4476,15 +4459,37 @@ main(int argc, char** argv)
> >   				prev_time = cur_time;
> >   				rte_delay_us_sleep(US_PER_S);
> >   			}
> > -		}
> > +		} else {
> > +			char c;
> > +			fd_set fds;
> >   
> > -		printf("Press enter to exit\n");
> > -		rc = read(0, &c, 1);
> > -		pmd_test_exit();
> > -		if (rc < 0)
> > -			return 1;
> > +			printf("Press enter to exit\n");
> > +
> > +			FD_ZERO(&fds);
> > +			FD_SET(0, &fds);
> > +
> > +			if (select(1, &fds, NULL, NULL, NULL) <= 0) {
> > +				fprintf(stderr, "Select failed: %s\n",
> > +					strerror(errno));  
> 
> Why is select() needed? Wouldn't a blocking read suffice? Or getchar().

On Linux, signal set SA_RESTART so a simple read is not interrupted.
One option was to use sigaction() which allows controlling flags, but that
won't work on Windows.  Using select() works on both.