[PATCH v4 0/3] tracing: Support poll on event hist file

[PATCH v4 0/3] tracing: Support poll on event hist file

[Masami Hiramatsu (Google)]

Hi,

Here is the v4 patch to support polling on event 'hist' file.
The previous version is here;

https://lore.kernel.org/all/172359427367.323666.6446548762874507863.stgit@devnote2/

This version uses getopt() in poll test command in [3/3] according to
Shuah's comment in the previous thread.

Background
----------
There has been interest in allowing user programs to monitor kernel
events in real time. Ftrace provides `trace_pipe` interface to wait
on events in the ring buffer, but it is needed to wait until filling
up a page with events in the ring buffer. We can also peek the
`trace` file periodically, but that is inefficient way to monitor
a randomely happening event.

Overview
--------
This patch set allows user to `poll`(or `select`, `epoll`) on event
histogram interface. As you know each event has its own `hist` file
which shows histograms generated by trigger action. So user can set
a new hist trigger on any event you want to monitor, and poll on the
`hist` file until it is updated.

There are 2 poll events are supported, POLLIN and POLLPRI. POLLIN
means that there are any readable update on `hist` file and this
event will be flashed only when you call read(). So, this is
useful if you want to read the histogram periodically.
The other POLLPRI event is for monitoring trace event. Like the
POLLIN, this will be returned when the histogram is updated, but
you don't need to read() the file and use poll() again.

Note that this waits for histogram update (not event arrival), thus
you must set a histogram on the event at first.

Usage
-----
Here is an example usage:

----
TRACEFS=/sys/kernel/tracing
EVENT=$TRACEFS/events/sched/sched_process_free

# setup histogram trigger and enable event
echo "hist:key=comm" >> $EVENT/trigger
echo 1 > $EVENT/enable

# Wait for update
poll pri $EVENT/hist

# Event arrived.
echo "process free event is comming"
tail $TRACEFS/trace
----

The 'poll' command is in the selftest patch.

You can take this series also from here;

https://git.kernel.org/pub/scm/linux/kernel/git/mhiramat/linux.git/log/?h=topic/event-hist-poll

Thank you,

---

Masami Hiramatsu (Google) (3):
      tracing/hist: Add poll(POLLIN) support on hist file
      tracing/hist: Support POLLPRI event for poll on histogram
      selftests/tracing: Add hist poll() support test


 include/linux/trace_events.h                       |    5 +
 kernel/trace/trace_events.c                        |   18 ++++
 kernel/trace/trace_events_hist.c                   |  101 +++++++++++++++++++-
 tools/testing/selftests/ftrace/Makefile            |    2 
 tools/testing/selftests/ftrace/poll.c              |   74 +++++++++++++++
 .../ftrace/test.d/trigger/trigger-hist-poll.tc     |   74 +++++++++++++++
 6 files changed, 271 insertions(+), 3 deletions(-)
 create mode 100644 tools/testing/selftests/ftrace/poll.c
 create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-poll.tc

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

[PATCH v4 1/3] tracing/hist: Add poll(POLLIN) support on hist file

[Masami Hiramatsu (Google)]

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

Add poll syscall support on the `hist` file. The Waiter will be waken
up when the histogram is updated with POLLIN.

Currently, there is no way to wait for a specific event in userspace.
So user needs to peek the `trace` periodicaly, or wait on `trace_pipe`.
But that is not good idea to peek the `trace` for the event randomely
happens. And `trace_pipe` is not coming back until a page is filled
with events.

This allows user to wait for a specific events on `hist` file. User
can set a histogram trigger on the event which they want to monitor.
And poll() on its `hist` file. Since this poll() returns POLLIN,
the next poll() will return soon unless you do read() on hist file.

NOTE: To read the hist file again, you must set the file offset to 0,
but just for monitoring the event, you may not need to read the
histogram.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Tom Zanussi <zanussi@kernel.org>
---
 include/linux/trace_events.h     |    5 +++
 kernel/trace/trace_events.c      |   18 +++++++++
 kernel/trace/trace_events_hist.c |   76 +++++++++++++++++++++++++++++++++++++-
 3 files changed, 96 insertions(+), 3 deletions(-)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 42bedcddd511..f3ec67d34097 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -663,6 +663,11 @@ struct trace_event_file {
 	struct trace_subsystem_dir	*system;
 	struct list_head		triggers;
 
+#ifdef CONFIG_HIST_TRIGGERS
+	struct irq_work			hist_work;
+	wait_queue_head_t		hist_wq;
+#endif
+
 	/*
 	 * 32 bit flags:
 	 *   bit 0:		enabled
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 7266ec2a4eea..0f077b32eea4 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -2972,6 +2972,20 @@ static bool event_in_systems(struct trace_event_call *call,
 	return !*p || isspace(*p) || *p == ',';
 }
 
+#ifdef CONFIG_HIST_TRIGGERS
+/*
+ * Wake up waiter on the hist_wq from irq_work because the hist trigger
+ * may happen in any context.
+ */
+static void hist_event_irq_work(struct irq_work *work)
+{
+	struct trace_event_file *event_file;
+
+	event_file = container_of(work, struct trace_event_file, hist_work);
+	wake_up_all(&event_file->hist_wq);
+}
+#endif
+
 static struct trace_event_file *
 trace_create_new_event(struct trace_event_call *call,
 		       struct trace_array *tr)
@@ -3004,6 +3018,10 @@ trace_create_new_event(struct trace_event_call *call,
 	INIT_LIST_HEAD(&file->triggers);
 	list_add(&file->list, &tr->events);
 	refcount_set(&file->ref, 1);
+#ifdef CONFIG_HIST_TRIGGERS
+	init_irq_work(&file->hist_work, hist_event_irq_work);
+	init_waitqueue_head(&file->hist_wq);
+#endif
 
 	return file;
 }
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 5f9119eb7c67..d27b60f54f68 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -5314,6 +5314,9 @@ static void event_hist_trigger(struct event_trigger_data *data,
 
 	if (resolve_var_refs(hist_data, key, var_ref_vals, true))
 		hist_trigger_actions(hist_data, elt, buffer, rec, rbe, key, var_ref_vals);
+
+	if (hist_data->event_file && wq_has_sleeper(&hist_data->event_file->hist_wq))
+		irq_work_queue(&hist_data->event_file->hist_work);
 }
 
 static void hist_trigger_stacktrace_print(struct seq_file *m,
@@ -5593,15 +5596,36 @@ static void hist_trigger_show(struct seq_file *m,
 		   n_entries, (u64)atomic64_read(&hist_data->map->drops));
 }
 
+struct hist_file_data {
+	struct file *file;
+	u64 last_read;
+};
+
+static u64 get_hist_hit_count(struct trace_event_file *event_file)
+{
+	struct hist_trigger_data *hist_data;
+	struct event_trigger_data *data;
+	u64 ret = 0;
+
+	list_for_each_entry(data, &event_file->triggers, list) {
+		if (data->cmd_ops->trigger_type == ETT_EVENT_HIST) {
+			hist_data = data->private_data;
+			ret += atomic64_read(&hist_data->map->hits);
+		}
+	}
+	return ret;
+}
+
 static int hist_show(struct seq_file *m, void *v)
 {
+	struct hist_file_data *hist_file = m->private;
 	struct event_trigger_data *data;
 	struct trace_event_file *event_file;
 	int n = 0, ret = 0;
 
 	mutex_lock(&event_mutex);
 
-	event_file = event_file_file(m->private);
+	event_file = event_file_file(hist_file->file);
 	if (unlikely(!event_file)) {
 		ret = -ENODEV;
 		goto out_unlock;
@@ -5611,6 +5635,7 @@ static int hist_show(struct seq_file *m, void *v)
 		if (data->cmd_ops->trigger_type == ETT_EVENT_HIST)
 			hist_trigger_show(m, data, n++);
 	}
+	hist_file->last_read = get_hist_hit_count(event_file);
 
  out_unlock:
 	mutex_unlock(&event_mutex);
@@ -5618,24 +5643,69 @@ static int hist_show(struct seq_file *m, void *v)
 	return ret;
 }
 
+static __poll_t event_hist_poll(struct file *file, struct poll_table_struct *wait)
+{
+	struct trace_event_file *event_file;
+	struct seq_file *m = file->private_data;
+	struct hist_file_data *hist_file = m->private;
+	__poll_t ret = 0;
+
+	mutex_lock(&event_mutex);
+
+	event_file = event_file_data(file);
+	if (!event_file) {
+		ret = EPOLLERR;
+		goto out_unlock;
+	}
+
+	poll_wait(file, &event_file->hist_wq, wait);
+
+	if (hist_file->last_read != get_hist_hit_count(event_file))
+		ret = EPOLLIN | EPOLLRDNORM;
+
+out_unlock:
+	mutex_unlock(&event_mutex);
+
+	return ret;
+}
+
+static int event_hist_release(struct inode *inode, struct file *file)
+{
+	struct seq_file *m = file->private_data;
+	struct hist_file_data *hist_file = m->private;
+
+	kfree(hist_file);
+	return tracing_single_release_file_tr(inode, file);
+}
+
 static int event_hist_open(struct inode *inode, struct file *file)
 {
+	struct hist_file_data *hist_file;
 	int ret;
 
 	ret = tracing_open_file_tr(inode, file);
 	if (ret)
 		return ret;
 
+	hist_file = kzalloc(sizeof(*hist_file), GFP_KERNEL);
+	if (!hist_file)
+		return -ENOMEM;
+	hist_file->file = file;
+
 	/* Clear private_data to avoid warning in single_open() */
 	file->private_data = NULL;
-	return single_open(file, hist_show, file);
+	ret = single_open(file, hist_show, hist_file);
+	if (ret)
+		kfree(hist_file);
+	return ret;
 }
 
 const struct file_operations event_hist_fops = {
 	.open = event_hist_open,
 	.read = seq_read,
 	.llseek = seq_lseek,
-	.release = tracing_single_release_file_tr,
+	.release = event_hist_release,
+	.poll = event_hist_poll,
 };
 
 #ifdef CONFIG_HIST_TRIGGERS_DEBUG

[PATCH v4 2/3] tracing/hist: Support POLLPRI event for poll on histogram

[Masami Hiramatsu (Google)]

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

Since POLLIN will not be flashed until read the hist file, user needs
to repeat read() and poll() on hist for monitoring the event
continuously. But the read() is somewhat redundant only for monitoring
events.

This add POLLPRI poll event on hist, this event returns when a histogram
is updated after open(), poll() or read(). Thus it is possible to wait
next event without read().

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Tom Zanussi <zanussi@kernel.org>
---
 kernel/trace/trace_events_hist.c |   29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index d27b60f54f68..d64aa34892e7 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -5599,6 +5599,7 @@ static void hist_trigger_show(struct seq_file *m,
 struct hist_file_data {
 	struct file *file;
 	u64 last_read;
+	u64 last_act;
 };
 
 static u64 get_hist_hit_count(struct trace_event_file *event_file)
@@ -5636,6 +5637,11 @@ static int hist_show(struct seq_file *m, void *v)
 			hist_trigger_show(m, data, n++);
 	}
 	hist_file->last_read = get_hist_hit_count(event_file);
+	/*
+	 * Update last_act too so that poll()/POLLPRI can wait for the next
+	 * event after any syscall on hist file.
+	 */
+	hist_file->last_act = hist_file->last_read;
 
  out_unlock:
 	mutex_unlock(&event_mutex);
@@ -5649,6 +5655,7 @@ static __poll_t event_hist_poll(struct file *file, struct poll_table_struct *wai
 	struct seq_file *m = file->private_data;
 	struct hist_file_data *hist_file = m->private;
 	__poll_t ret = 0;
+	u64 cnt;
 
 	mutex_lock(&event_mutex);
 
@@ -5660,8 +5667,13 @@ static __poll_t event_hist_poll(struct file *file, struct poll_table_struct *wai
 
 	poll_wait(file, &event_file->hist_wq, wait);
 
-	if (hist_file->last_read != get_hist_hit_count(event_file))
-		ret = EPOLLIN | EPOLLRDNORM;
+	cnt = get_hist_hit_count(event_file);
+	if (hist_file->last_read != cnt)
+		ret |= EPOLLIN | EPOLLRDNORM;
+	if (hist_file->last_act != cnt) {
+		hist_file->last_act = cnt;
+		ret |= EPOLLPRI;
+	}
 
 out_unlock:
 	mutex_unlock(&event_mutex);
@@ -5680,6 +5692,7 @@ static int event_hist_release(struct inode *inode, struct file *file)
 
 static int event_hist_open(struct inode *inode, struct file *file)
 {
+	struct trace_event_file *event_file;
 	struct hist_file_data *hist_file;
 	int ret;
 
@@ -5690,13 +5703,25 @@ static int event_hist_open(struct inode *inode, struct file *file)
 	hist_file = kzalloc(sizeof(*hist_file), GFP_KERNEL);
 	if (!hist_file)
 		return -ENOMEM;
+
+	mutex_lock(&event_mutex);
+	event_file = event_file_data(file);
+	if (!event_file) {
+		ret = -ENODEV;
+		goto out_unlock;
+	}
+
 	hist_file->file = file;
+	hist_file->last_act = get_hist_hit_count(event_file);
 
 	/* Clear private_data to avoid warning in single_open() */
 	file->private_data = NULL;
 	ret = single_open(file, hist_show, hist_file);
+
+out_unlock:
 	if (ret)
 		kfree(hist_file);
+	mutex_unlock(&event_mutex);
 	return ret;
 }
 

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

[Masami Hiramatsu (Google)]

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 */
+	if (ret == 0)
+		return 1;
+
+	return 0;
+}
diff --git a/tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-poll.tc b/tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-poll.tc
new file mode 100644
index 000000000000..cbd01a71ecad
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-poll.tc
@@ -0,0 +1,74 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: event trigger - test poll wait on histogram
+# requires: set_event events/sched/sched_process_free/trigger events/sched/sched_process_free/hist
+# flags: instance
+
+POLL=${FTRACETEST_ROOT}/poll
+
+if [ ! -x ${POLL} ]; then
+  echo "poll program is not compiled!"
+  exit_unresolved
+fi
+
+EVENT=events/sched/sched_process_free/
+
+# Check poll ops is supported. Before implementing poll on hist file, it
+# returns soon with POLLIN | POLLOUT, but not POLLPRI.
+
+# This must wait >1 sec and return 1 (timeout).
+set +e
+${POLL} -I -t 1000 ${EVENT}/hist
+ret=$?
+set -e
+if [ ${ret} != 1 ]; then
+  echo "poll on hist file is not supported"
+  exit_unsupported
+fi
+
+# Test POLLIN
+echo > trace
+echo "hist:key=comm" > ${EVENT}/trigger
+echo 1 > ${EVENT}/enable
+
+# This sleep command will exit after 2 seconds.
+sleep 2 &
+BGPID=$!
+# if timeout happens, poll returns 1.
+${POLL} -I -t 4000 ${EVENT}/hist
+echo 0 > tracing_on
+
+if [ -d /proc/${BGPID} ]; then
+  echo "poll exits too soon"
+  kill -KILL ${BGPID} ||:
+  exit_fail
+fi
+
+if ! grep -qw "sleep" trace; then
+  echo "poll exits before event happens"
+  exit_fail
+fi
+
+# Test POLLPRI
+echo > trace
+echo 1 > tracing_on
+
+# This sleep command will exit after 2 seconds.
+sleep 2 &
+BGPID=$!
+# if timeout happens, poll returns 1.
+${POLL} -P -t 4000 ${EVENT}/hist
+echo 0 > tracing_on
+
+if [ -d /proc/${BGPID} ]; then
+  echo "poll exits too soon"
+  kill -KILL ${BGPID} ||:
+  exit_fail
+fi
+
+if ! grep -qw "sleep" trace; then
+  echo "poll exits before event happens"
+  exit_fail
+fi
+
+exit_pass

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

[Shuah Khan]

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.

With this fixed

Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>

thanks,
-- Shuah

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

[Masami Hiramatsu]

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.

> With this fixed
> 
> Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>

Thanks!

> 
> thanks,
> -- Shuah


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

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

[Masami Hiramatsu]

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>