[PATCH v7 0/3] tracing: Support poll on event hist file

[PATCH v7 0/3] tracing: Support poll on event hist file

[Masami Hiramatsu (Google)]

Hi,

Here is the 7th version of the series to support polling on event 'hist' file.
The previous version is here;

https://lore.kernel.org/all/172907575534.470540.12941248697563459082.stgit@mhiramat.roam.corp.google.com/

This version updates descriptions, use guard() for mutex and fixes
selftest problem.

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                       |   14 +++
 kernel/trace/trace_events.c                        |   14 +++
 kernel/trace/trace_events_hist.c                   |   92 +++++++++++++++++++-
 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, 267 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 v7 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 it is not a good idea to peek at the `trace` for an event that
randomly happens. And `trace_pipe` is not coming back until a page is
filled with events.

This allows a user to wait for a specific event on the `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 a read() happens on that 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>
---
 Changes in v7:
   - Reword description according to Steve's comment.
   - Use guard() for mutex.
---
 include/linux/trace_events.h     |   14 ++++++++
 kernel/trace/trace_events.c      |   14 ++++++++
 kernel/trace/trace_events_hist.c |   69 ++++++++++++++++++++++++++++++++++++--
 3 files changed, 94 insertions(+), 3 deletions(-)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 2a5df5b62cfc..47caca4e7ff4 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -669,6 +669,20 @@ struct trace_event_file {
 	atomic_t		tm_ref;	/* trigger-mode reference counter */
 };
 
+#ifdef CONFIG_HIST_TRIGGERS
+extern struct irq_work hist_poll_work;
+extern wait_queue_head_t hist_poll_wq;
+
+static inline void hist_poll_wakeup(void)
+{
+	if (wq_has_sleeper(&hist_poll_wq))
+		irq_work_queue(&hist_poll_work);
+}
+
+#define hist_poll_wait(file, wait)	\
+	poll_wait(file, &hist_poll_wq, wait)
+#endif
+
 #define __TRACE_EVENT_FLAGS(name, value)				\
 	static int __init trace_init_flags_##name(void)			\
 	{								\
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 77e68efbd43e..e34b4a88d8ec 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_poll_wq from irq_work because the hist trigger
+ * may happen in any context.
+ */
+static void hist_poll_event_irq_work(struct irq_work *work)
+{
+	wake_up_all(&hist_poll_wq);
+}
+
+DEFINE_IRQ_WORK(hist_poll_work, hist_poll_event_irq_work);
+DECLARE_WAIT_QUEUE_HEAD(hist_poll_wq);
+#endif
+
 static struct trace_event_file *
 trace_create_new_event(struct trace_event_call *call,
 		       struct trace_array *tr)
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 9c058aa8baf3..e169f67c6088 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -5311,6 +5311,8 @@ 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);
+
+	hist_poll_wakeup();
 }
 
 static void hist_trigger_stacktrace_print(struct seq_file *m,
@@ -5590,15 +5592,36 @@ 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;
@@ -5608,6 +5631,7 @@ 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);
@@ -5615,24 +5639,63 @@ 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;
+
+	guard(mutex)(&event_mutex);
+
+	event_file = event_file_data(file);
+	if (!event_file)
+		return EPOLLERR;
+
+	hist_poll_wait(file, wait);
+
+	if (hist_file->last_read != get_hist_hit_count(event_file))
+		return EPOLLIN | EPOLLRDNORM;
+
+	return 0;
+}
+
+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 v7 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 flushed until the hist file is read, the user
needs to repeatedly read() and poll() on the hist file for monitoring the
event continuously. But the read() is somewhat redundant when the user is
only monitoring for event updates.

Add POLLPRI poll event on the hist file so the event returns when a
histogram is updated after open(), poll() or read(). Thus it is possible
to wait for the next event without having to issue a read().

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Tom Zanussi <zanussi@kernel.org>
---
 Changes in v7:
  - Reword description according to Steve's comment.
  - Use guard() in hist_poll_open().
---
 kernel/trace/trace_events_hist.c |   29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index e169f67c6088..15f76c681c6c 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -5595,6 +5595,7 @@ 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)
@@ -5632,6 +5633,11 @@ 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);
@@ -5644,6 +5650,8 @@ static __poll_t event_hist_poll(struct file *file, struct poll_table_struct *wai
 	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;
+	u64 cnt;
 
 	guard(mutex)(&event_mutex);
 
@@ -5653,10 +5661,15 @@ static __poll_t event_hist_poll(struct file *file, struct poll_table_struct *wai
 
 	hist_poll_wait(file, wait);
 
-	if (hist_file->last_read != get_hist_hit_count(event_file))
-		return 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;
+	}
 
-	return 0;
+	return ret;
 }
 
 static int event_hist_release(struct inode *inode, struct file *file)
@@ -5670,6 +5683,7 @@ 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;
 
@@ -5677,16 +5691,25 @@ static int event_hist_open(struct inode *inode, struct file *file)
 	if (ret)
 		return ret;
 
+	guard(mutex)(&event_mutex);
+
+	event_file = event_file_data(file);
+	if (!event_file)
+		return -ENODEV;
+
 	hist_file = kzalloc(sizeof(*hist_file), GFP_KERNEL);
 	if (!hist_file)
 		return -ENOMEM;
+
 	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);
 	if (ret)
 		kfree(hist_file);
+
 	return ret;
 }
 

[PATCH v7 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>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
---
 Changes in v7:
  - Add comm histogram filter for specifying test sleep command.
---
 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..53258f7515e7
--- /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 (ret == 0), exit code is 1 */
+	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 v7 3/3] selftests/tracing: Add hist poll() support test

[Masami Hiramatsu]

On Fri, 27 Dec 2024 13:08:18 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> 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>
> Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
> ---
>  Changes in v7:
>   - Add comm histogram filter for specifying test sleep command.

I found I forgot to refresh the patch. (just not committed)

Sorry.

> ---
>  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..53258f7515e7
> --- /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 (ret == 0), exit code is 1 */
> +	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
> 


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

[PATCH v7.1 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>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
---
 Changes in v7:
  - Add comm histogram filter for specifying test sleep command.
---
 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..53258f7515e7
--- /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 (ret == 0), exit code is 1 */
+	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..8d275e3238d9
--- /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 if comm =="sleep"' > ${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