Re: [PATCH v4 3/3] selftests/tracing: Add hist poll() support test

Masami Hiramatsu
2024-08-18T13:16:02Z

On Sun, 18 Aug 2024 00:06:20 +0900
Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:

> On Fri, 16 Aug 2024 08:04:41 -0600
> Shuah Khan <skhan@linuxfoundation.org> wrote:
>
> > On 8/15/24 20:31, Masami Hiramatsu (Google) wrote:
> > > From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > >
> > > Add a testcase for poll() on hist file. This introduces a helper binary
> > > to the ftracetest, because there is no good way to reliably execute
> > > poll() on hist file.
> > >
> > > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > > ---
> > > Changes in v4:
> > > - Use getopt() in poll.c (command options are changed)
> > > - Update test code according to the new command options.
> > > Changes in v2:
> > > - Update poll command to support both of POLLIN and POLLPRI, and timeout.
> > > - Identify unsupported stable kernel if poll-in returns soon.
> > > - Test both of POLLIN and POLLPRI.
> > > ---
> > > tools/testing/selftests/ftrace/Makefile | 2 +
> > > tools/testing/selftests/ftrace/poll.c | 74 ++++++++++++++++++++
> > > .../ftrace/test.d/trigger/trigger-hist-poll.tc | 74 ++++++++++++++++++++
> > > 3 files changed, 150 insertions(+)
> > > create mode 100644 tools/testing/selftests/ftrace/poll.c
> > > create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-poll.tc
> > >
> > > diff --git a/tools/testing/selftests/ftrace/Makefile b/tools/testing/selftests/ftrace/Makefile
> > > index a1e955d2de4c..49d96bb16355 100644
> > > --- a/tools/testing/selftests/ftrace/Makefile
> > > +++ b/tools/testing/selftests/ftrace/Makefile
> > > @@ -6,4 +6,6 @@ TEST_PROGS := ftracetest-ktap
> > > TEST_FILES := test.d settings
> > > EXTRA_CLEAN := $(OUTPUT)/logs/*
> > >
> > > +TEST_GEN_PROGS = poll
> > > +
> > > include ../lib.mk
> > > diff --git a/tools/testing/selftests/ftrace/poll.c b/tools/testing/selftests/ftrace/poll.c
> > > new file mode 100644
> > > index 000000000000..584f159654b1
> > > --- /dev/null
> > > +++ b/tools/testing/selftests/ftrace/poll.c
> > > @@ -0,0 +1,74 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +/*
> > > + * Simple poll on a file.
> > > + *
> > > + * Copyright (c) 2024 Google LLC.
> > > + */
> > > +
> > > +#include <errno.h>
> > > +#include <fcntl.h>
> > > +#include <poll.h>
> > > +#include <stdio.h>
> > > +#include <stdlib.h>
> > > +#include <string.h>
> > > +#include <unistd.h>
> > > +
> > > +#define BUFSIZE 4096
> > > +
> > > +/*
> > > + * Usage:
> > > + * poll [-I|-P] [-t timeout] FILE
> > > + */
> > > +int main(int argc, char *argv[])
> > > +{
> > > + struct pollfd pfd = {.events = POLLIN};
> > > + char buf[BUFSIZE];
> > > + int timeout = -1;
> > > + int ret, opt;
> > > +
> > > + while ((opt = getopt(argc, argv, "IPt:")) != -1) {
> > > + switch (opt) {
> > > + case 'I':
> > > + pfd.events = POLLIN;
> > > + break;
> > > + case 'P':
> > > + pfd.events = POLLPRI;
> > > + break;
> > > + case 't':
> > > + timeout = atoi(optarg);
> > > + break;
> > > + default:
> > > + fprintf(stderr, "Usage: %s [-I|-P] [-t timeout] FILE\n",
> > > + argv[0]);
> > > + return -1;
> > > + }
> > > + }
> > > + if (optind >= argc) {
> > > + fprintf(stderr, "Error: Polling file is not specified\n");
> > > + return -1;
> > > + }
> > > +
> > > + pfd.fd = open(argv[optind], O_RDONLY);
> > > + if (pfd.fd < 0) {
> > > + fprintf(stderr, "failed to open %s", argv[optind]);
> > > + perror("open");
> > > + return -1;
> > > + }
> > > +
> > > + /* Reset poll by read if POLLIN is specified. */
> > > + if (pfd.events & POLLIN)
> > > + do {} while (read(pfd.fd, buf, BUFSIZE) == BUFSIZE);
> > > +
> > > + ret = poll(&pfd, 1, timeout);
> > > + if (ret < 0 && errno != EINTR) {
> > > + perror("poll");
> > > + return -1;
> > > + }
> > > + close(pfd.fd);
> > > +
> > > + /* If timeout happned, return code is 0 */
> >
> > Looks like you missed this one :) Otherwise looks good to me.
> >
> Oops, indeed.

Hm, this comment is correct but misleadable. I meant that the poll()
returns 0 if timeout happens.

-----
RETURN VALUE
On success, poll() returns a nonnegative value which is the number of elements in the
pollfds whose revents fields have been set to a nonzero value (indicating an event or an
error). A return value of zero indicates that the system call timed out before any file
descriptors became read.
-----

But the comment should tell what this command does.

Thanks,

>
> > With this fixed
> >
> > Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
>
> Thanks!
>
> >
> > thanks,
> > -- Shuah
>
>
> --
> Masami Hiramatsu (Google) <mhiramat@kernel.org>

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>