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

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Message-Id: <20240818221556.49146df39698986646a6c867@kernel.org>
Date: Sun, 18 Aug 2024 22:15:56 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Cc: Shuah Khan <skhan@...uxfoundation.org>, Steven Rostedt
 <rostedt@...dmis.org>, Shuah Khan <shuah@...nel.org>, Tom Zanussi
 <zanussi@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v4 3/3] selftests/tracing: Add hist poll() support test

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

> On Fri, 16 Aug 2024 08:04:41 -0600
> Shuah Khan <skhan@...uxfoundation.org> wrote:
> 
> > On 8/15/24 20:31, Masami Hiramatsu (Google) wrote:
> > > From: Masami Hiramatsu (Google) <mhiramat@...nel.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@...nel.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@...uxfoundation.org>
> 
> Thanks!
> 
> > 
> > thanks,
> > -- Shuah
> 
> 
> -- 
> Masami Hiramatsu (Google) <mhiramat@...nel.org>


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