RE: [PATCH 2/3] perf kvm: Allow running without stdin

From: Lubashev, Igor
Date: Wed Oct 23 2019 - 12:07:16 EST


> On Wed, Oct 23, 2019 at 6:43 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> On Tue, Oct 22, 2019 at 09:54:52PM -0400, Igor Lubashev wrote:
> > Allow perf kvm --stdio to run without access to stdin.
> > This lets perf kvm to run in a batch mode until interrupted.
> >
> > The following now works as expected:
> >
> > $ perf kvm top --stdio < /dev/null
> >
> > Signed-off-by: Igor Lubashev <ilubashe@xxxxxxxxxx>
> > ---
> > tools/perf/builtin-kvm.c | 33 ++++++++++++++++++++-------------
> > 1 file changed, 20 insertions(+), 13 deletions(-)
> >
> > diff --git a/tools/perf/builtin-kvm.c b/tools/perf/builtin-kvm.c index
> > 858da896b518..5217aa3596c7 100644
> > --- a/tools/perf/builtin-kvm.c
> > +++ b/tools/perf/builtin-kvm.c
> > @@ -930,18 +930,20 @@ static int fd_set_nonblock(int fd)
> >
> > static int perf_kvm__handle_stdin(void) {
> > - int c;
> > -
> > - c = getc(stdin);
> > - if (c == 'q')
> > + switch (getc(stdin)) {
> > + case 'q':
> > + done = 1;
> > return 1;
> > -
> > - return 0;
> > + case EOF:
> > + return 0;
> > + default:
> > + return 1;
> > + }
> > }
> >
> > static int kvm_events_live_report(struct perf_kvm_stat *kvm) {
> > - int nr_stdin, ret, err = -EINVAL;
> > + int nr_stdin = -1, ret, err = -EINVAL;
> > struct termios save;
> >
> > /* live flag must be set first */
> > @@ -972,13 +974,16 @@ static int kvm_events_live_report(struct
> perf_kvm_stat *kvm)
> > if (evlist__add_pollfd(kvm->evlist, kvm->timerfd) < 0)
> > goto out;
> >
> > - nr_stdin = evlist__add_pollfd(kvm->evlist, fileno(stdin));
> > - if (nr_stdin < 0)
> > - goto out;
> > -
> > if (fd_set_nonblock(fileno(stdin)) != 0)
> > goto out;
> >
> > + /* add stdin, if it is connected */
> > + if (getc(stdin) != EOF) {
> > + nr_stdin = evlist__add_pollfd(kvm->evlist, fileno(stdin));
> > + if (nr_stdin < 0)
> > + goto out;
> > + }
> > +
> > /* everything is good - enable the events and process */
> > evlist__enable(kvm->evlist);
> >
> > @@ -994,8 +999,10 @@ static int kvm_events_live_report(struct
> perf_kvm_stat *kvm)
> > if (err)
> > goto out;
> >
> > - if (fda->entries[nr_stdin].revents & POLLIN)
> > - done = perf_kvm__handle_stdin();
> > + if (nr_stdin >= 0 && fda->entries[nr_stdin].revents & POLLIN)
> {
> > + if (!perf_kvm__handle_stdin())
>
> can this return 0 ? if stdin is EOF then nr_stdin stays -1
>
> > + fda->entries[nr_stdin].events = 0;
>
> why do you need to set events to 0 in here?

Otherwise poll() would wakeup continually, since an EOF stdin is already ready for POLLIN.

- Igor

> thanks,
> jirka