[PATCH V2 2/6] tracing/osnoise: Add osnoise/options file

Daniel Bristot de Oliveira
2022-11-23T17:06:47Z

Add the tracing/osnoise/options file to control osnoise/timerlat
tracer features. It is a single file to contain multiple features,
similar to the sched/features file.

Reading the file displays a list of options. Writing the OPTION_NAME
enables it, writing NO_OPTION_NAME disables it.

The DEAFULTS is a particular option that resets the options to the
default ones.

It uses a bitmask to keep track of the status of the option. When needed,
we can add a list of static keys, but for now it does not justify the
memory increase.

Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
---
kernel/trace/trace_osnoise.c | 170 +++++++++++++++++++++++++++++++++++
1 file changed, 170 insertions(+)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 4300c5dc4e5d..17b77fe3950b 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -48,6 +48,19 @@
#define DEFAULT_TIMERLAT_PERIOD 1000 /* 1ms */
#define DEFAULT_TIMERLAT_PRIO 95 /* FIFO 95 */

+/*
+ * osnoise/options entries.
+ */
+enum osnoise_options_index {
+ OSN_DEFAULTS = 0,
+ OSN_MAX
+};
+
+static const char * const osnoise_options_str[OSN_MAX] = { "DEFAULTS" };
+
+#define OSN_DEFAULT_OPTIONS 0
+unsigned long osnoise_options = OSN_DEFAULT_OPTIONS;
+
/*
* trace_array of the enabled osnoise/timerlat instances.
*/
@@ -1860,6 +1873,150 @@ static void osnoise_init_hotplug_support(void)
}
#endif /* CONFIG_HOTPLUG_CPU */

+/*
+ * seq file functions for the osnoise/options file.
+ */
+static void *s_options_start(struct seq_file *s, loff_t *pos)
+{
+ int option = *pos;
+
+ mutex_lock(&interface_lock);
+
+ if (option >= OSN_MAX)
+ return NULL;
+
+ return pos;
+}
+
+static void *s_options_next(struct seq_file *s, void *v, loff_t *pos)
+{
+ int option = ++(*pos);
+
+ if (option >= OSN_MAX)
+ return NULL;
+
+ return pos;
+}
+
+static int s_options_show(struct seq_file *s, void *v)
+{
+ loff_t *pos = v;
+ int option = *pos;
+
+ if (option == OSN_DEFAULTS) {
+ if (osnoise_options == OSN_DEFAULT_OPTIONS)
+ seq_printf(s, "%s", osnoise_options_str[option]);
+ else
+ seq_printf(s, "NO_%s", osnoise_options_str[option]);
+ goto out;
+ }
+
+ if (test_bit(option, &osnoise_options))
+ seq_printf(s, "%s", osnoise_options_str[option]);
+ else
+ seq_printf(s, "NO_%s", osnoise_options_str[option]);
+
+out:
+ if (option != OSN_MAX)
+ seq_puts(s, " ");
+
+ return 0;
+}
+
+static void s_options_stop(struct seq_file *s, void *v)
+{
+ seq_puts(s, "\n");
+ mutex_unlock(&interface_lock);
+}
+
+static const struct seq_operations osnoise_options_seq_ops = {
+ .start = s_options_start,
+ .next = s_options_next,
+ .show = s_options_show,
+ .stop = s_options_stop
+};
+
+static int osnoise_options_open(struct inode *inode, struct file *file)
+{
+ return seq_open(file, &osnoise_options_seq_ops);
+};
+
+/**
+ * osnoise_options_write - Write function for "options" entry
+ * @filp: The active open file structure
+ * @ubuf: The user buffer that contains the value to write
+ * @cnt: The maximum number of bytes to write to "file"
+ * @ppos: The current position in @file
+ *
+ * Writing the option name sets the option, writing the "NO_"
+ * prefix in front of the option name disables it.
+ *
+ * Writing "DEFAULTS" resets the option values to the default ones.
+ */
+static ssize_t osnoise_options_write(struct file *filp, const char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ int running, option, enable, retval;
+ char buf[256], *option_str;
+
+ if (cnt >= 256)
+ return -EINVAL;
+
+ if (copy_from_user(buf, ubuf, cnt))
+ return -EFAULT;
+
+ buf[cnt] = 0;
+
+ if (strncmp(buf, "NO_", 3)) {
+ option_str = strstrip(buf);
+ enable = true;
+ } else {
+ option_str = strstrip(&buf[3]);
+ enable = false;
+ }
+
+ option = match_string(osnoise_options_str, OSN_MAX, option_str);
+ if (option < 0)
+ return -EINVAL;
+
+ /*
+ * trace_types_lock is taken to avoid concurrency on start/stop.
+ */
+ mutex_lock(&trace_types_lock);
+ running = osnoise_has_registered_instances();
+ if (running)
+ stop_per_cpu_kthreads();
+
+ mutex_lock(&interface_lock);
+ /*
+ * avoid CPU hotplug operations that might read options.
+ */
+ cpus_read_lock();
+
+ retval = cnt;
+
+ if (enable) {
+ if (option == OSN_DEFAULTS)
+ osnoise_options = OSN_DEFAULT_OPTIONS;
+ else
+ set_bit(option, &osnoise_options);
+ } else {
+ if (option == OSN_DEFAULTS)
+ retval = -EINVAL;
+ else
+ clear_bit(option, &osnoise_options);
+ }
+
+ cpus_read_unlock();
+ mutex_unlock(&interface_lock);
+
+ if (running)
+ start_per_cpu_kthreads();
+ mutex_unlock(&trace_types_lock);
+
+ return retval;
+}
+
/*
* osnoise_cpus_read - Read function for reading the "cpus" file
* @filp: The active open file structure
@@ -2042,6 +2199,14 @@ static const struct file_operations cpus_fops = {
.llseek = generic_file_llseek,
};

+static const struct file_operations osnoise_options_fops = {
+ .open = osnoise_options_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = seq_release,
+ .write = osnoise_options_write
+};
+
#ifdef CONFIG_TIMERLAT_TRACER
#ifdef CONFIG_STACKTRACE
static int init_timerlat_stack_tracefs(struct dentry *top_dir)
@@ -2128,6 +2293,11 @@ static int init_tracefs(void)
if (!tmp)
goto err;

+ tmp = trace_create_file("options", TRACE_MODE_WRITE, top_dir, NULL,
+ &osnoise_options_fops);
+ if (!tmp)
+ goto err;
+
ret = init_timerlat_tracefs(top_dir);
if (ret)
goto err;
--
2.32.0