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Subject[PATCH v4 07/12] tracing: Add synth_event_trace() and related functions
Date
Add an exported function named synth_event_trace(), allowing modules
or other kernel code to trace synthetic events.

Also added are several functions that allow the same functionality to
be broken out in a piecewise fashion, which are useful in situations
where tracing an event from a full array of values would be
cumbersome. Those functions are synth_event_trace_start/end() and
synth_event_add_(next)_val().

Signed-off-by: Tom Zanussi <zanussi@kernel.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
---
include/linux/trace_events.h | 26 +++
kernel/trace/trace_events_hist.c | 463 +++++++++++++++++++++++++++++++++++++++
2 files changed, 489 insertions(+)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 07b83532a3c6..bf03d12efb28 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -416,6 +416,32 @@ extern int synth_event_add_fields(struct dynevent_cmd *cmd,
#define synth_event_gen_cmd_end(cmd) \
dynevent_create(cmd)

+struct synth_event;
+
+struct synth_event_trace_state {
+ struct trace_event_buffer fbuffer;
+ struct synth_trace_event *entry;
+ struct trace_buffer *buffer;
+ struct synth_event *event;
+ unsigned int cur_field;
+ unsigned int n_u64;
+ bool enabled;
+ bool add_next;
+ bool add_name;
+};
+
+extern int synth_event_trace(struct trace_event_file *file,
+ unsigned int n_vals, ...);
+extern int synth_event_trace_array(struct trace_event_file *file, u64 *vals,
+ unsigned int n_vals);
+extern int synth_event_trace_start(struct trace_event_file *file,
+ struct synth_event_trace_state *trace_state);
+extern int synth_event_add_next_val(u64 val,
+ struct synth_event_trace_state *trace_state);
+extern int synth_event_add_val(const char *field_name, u64 val,
+ struct synth_event_trace_state *trace_state);
+extern int synth_event_trace_end(struct synth_event_trace_state *trace_state);
+
/*
* Event file flags:
* ENABLED - The event is enabled
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 22cd7ecdfb92..2e88c9805f4b 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -398,6 +398,7 @@ struct synth_field {
char *type;
char *name;
size_t size;
+ unsigned int offset;
bool is_signed;
bool is_string;
};
@@ -668,6 +669,8 @@ static int synth_event_define_fields(struct trace_event_call *call)
if (ret)
break;

+ event->fields[i]->offset = n_u64;
+
if (event->fields[i]->is_string) {
offset += STR_VAR_LEN_MAX;
n_u64 += STR_VAR_LEN_MAX / sizeof(u64);
@@ -1786,6 +1789,466 @@ void synth_event_cmd_init(struct dynevent_cmd *cmd, char *buf, int maxlen)
}
EXPORT_SYMBOL_GPL(synth_event_cmd_init);

+/**
+ * synth_event_trace - Trace a synthetic event
+ * @file: The trace_event_file representing the synthetic event
+ * @n_vals: The number of values in vals
+ * @args: Variable number of args containing the event values
+ *
+ * Trace a synthetic event using the values passed in the variable
+ * argument list.
+ *
+ * The argument list should be a list 'n_vals' u64 values. The number
+ * of vals must match the number of field in the synthetic event, and
+ * must be in the same order as the synthetic event fields.
+ *
+ * All vals should be cast to u64, and string vals are just pointers
+ * to strings, cast to u64. Strings will be copied into space
+ * reserved in the event for the string, using these pointers.
+ *
+ * Return: 0 on success, err otherwise.
+ */
+int synth_event_trace(struct trace_event_file *file, unsigned int n_vals, ...)
+{
+ struct trace_event_buffer fbuffer;
+ struct synth_trace_event *entry;
+ struct trace_buffer *buffer;
+ struct synth_event *event;
+ unsigned int i, n_u64;
+ int fields_size = 0;
+ va_list args;
+ int ret = 0;
+
+ /*
+ * Normal event generation doesn't get called at all unless
+ * the ENABLED bit is set (which attaches the probe thus
+ * allowing this code to be called, etc). Because this is
+ * called directly by the user, we don't have that but we
+ * still need to honor not logging when disabled.
+ */
+ if (!(file->flags & EVENT_FILE_FL_ENABLED))
+ return 0;
+
+ event = file->event_call->data;
+
+ if (n_vals != event->n_fields)
+ return -EINVAL;
+
+ if (trace_trigger_soft_disabled(file))
+ return -EINVAL;
+
+ fields_size = event->n_u64 * sizeof(u64);
+
+ /*
+ * Avoid ring buffer recursion detection, as this event
+ * is being performed within another event.
+ */
+ buffer = file->tr->array_buffer.buffer;
+ ring_buffer_nest_start(buffer);
+
+ entry = trace_event_buffer_reserve(&fbuffer, file,
+ sizeof(*entry) + fields_size);
+ if (!entry) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ va_start(args, n_vals);
+ for (i = 0, n_u64 = 0; i < event->n_fields; i++) {
+ u64 val;
+
+ val = va_arg(args, u64);
+
+ if (event->fields[i]->is_string) {
+ char *str_val = (char *)(long)val;
+ char *str_field = (char *)&entry->fields[n_u64];
+
+ strscpy(str_field, str_val, STR_VAR_LEN_MAX);
+ n_u64 += STR_VAR_LEN_MAX / sizeof(u64);
+ } else {
+ entry->fields[n_u64] = val;
+ n_u64++;
+ }
+ }
+ va_end(args);
+
+ trace_event_buffer_commit(&fbuffer);
+out:
+ ring_buffer_nest_end(buffer);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(synth_event_trace);
+
+/**
+ * synth_event_trace_array - Trace a synthetic event from an array
+ * @file: The trace_event_file representing the synthetic event
+ * @vals: Array of values
+ * @n_vals: The number of values in vals
+ *
+ * Trace a synthetic event using the values passed in as 'vals'.
+ *
+ * The 'vals' array is just an array of 'n_vals' u64. The number of
+ * vals must match the number of field in the synthetic event, and
+ * must be in the same order as the synthetic event fields.
+ *
+ * All vals should be cast to u64, and string vals are just pointers
+ * to strings, cast to u64. Strings will be copied into space
+ * reserved in the event for the string, using these pointers.
+ *
+ * Return: 0 on success, err otherwise.
+ */
+int synth_event_trace_array(struct trace_event_file *file, u64 *vals,
+ unsigned int n_vals)
+{
+ struct trace_event_buffer fbuffer;
+ struct synth_trace_event *entry;
+ struct trace_buffer *buffer;
+ struct synth_event *event;
+ unsigned int i, n_u64;
+ int fields_size = 0;
+ int ret = 0;
+
+ /*
+ * Normal event generation doesn't get called at all unless
+ * the ENABLED bit is set (which attaches the probe thus
+ * allowing this code to be called, etc). Because this is
+ * called directly by the user, we don't have that but we
+ * still need to honor not logging when disabled.
+ */
+ if (!(file->flags & EVENT_FILE_FL_ENABLED))
+ return 0;
+
+ event = file->event_call->data;
+
+ if (n_vals != event->n_fields)
+ return -EINVAL;
+
+ if (trace_trigger_soft_disabled(file))
+ return -EINVAL;
+
+ fields_size = event->n_u64 * sizeof(u64);
+
+ /*
+ * Avoid ring buffer recursion detection, as this event
+ * is being performed within another event.
+ */
+ buffer = file->tr->array_buffer.buffer;
+ ring_buffer_nest_start(buffer);
+
+ entry = trace_event_buffer_reserve(&fbuffer, file,
+ sizeof(*entry) + fields_size);
+ if (!entry) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ for (i = 0, n_u64 = 0; i < event->n_fields; i++) {
+ if (event->fields[i]->is_string) {
+ char *str_val = (char *)(long)vals[i];
+ char *str_field = (char *)&entry->fields[n_u64];
+
+ strscpy(str_field, str_val, STR_VAR_LEN_MAX);
+ n_u64 += STR_VAR_LEN_MAX / sizeof(u64);
+ } else {
+ entry->fields[n_u64] = vals[i];
+ n_u64++;
+ }
+ }
+
+ trace_event_buffer_commit(&fbuffer);
+out:
+ ring_buffer_nest_end(buffer);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(synth_event_trace_array);
+
+/**
+ * synth_event_trace_start - Start piecewise synthetic event trace
+ * @file: The trace_event_file representing the synthetic event
+ * @trace_state: A pointer to object tracking the piecewise trace state
+ *
+ * Start the trace of a synthetic event field-by-field rather than all
+ * at once.
+ *
+ * This function 'opens' an event trace, which means space is reserved
+ * for the event in the trace buffer, after which the event's
+ * individual field values can be set through either
+ * synth_event_add_next_val() or synth_event_add_val().
+ *
+ * A pointer to a trace_state object is passed in, which will keep
+ * track of the current event trace state until the event trace is
+ * closed (and the event finally traced) using
+ * synth_event_trace_end().
+ *
+ * Note that synth_event_trace_end() must be called after all values
+ * have been added for each event trace, regardless of whether adding
+ * all field values succeeded or not.
+ *
+ * Note also that for a given event trace, all fields must be added
+ * using either synth_event_add_next_val() or synth_event_add_val()
+ * but not both together or interleaved.
+ *
+ * Return: 0 on success, err otherwise.
+ */
+int synth_event_trace_start(struct trace_event_file *file,
+ struct synth_event_trace_state *trace_state)
+{
+ struct synth_trace_event *entry;
+ int fields_size = 0;
+ int ret = 0;
+
+ if (!trace_state) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ memset(trace_state, '\0', sizeof(*trace_state));
+
+ /*
+ * Normal event tracing doesn't get called at all unless the
+ * ENABLED bit is set (which attaches the probe thus allowing
+ * this code to be called, etc). Because this is called
+ * directly by the user, we don't have that but we still need
+ * to honor not logging when disabled. For the the iterated
+ * trace case, we save the enabed state upon start and just
+ * ignore the following data calls.
+ */
+ if (!(file->flags & EVENT_FILE_FL_ENABLED)) {
+ trace_state->enabled = false;
+ goto out;
+ }
+
+ trace_state->enabled = true;
+
+ trace_state->event = file->event_call->data;
+
+ if (trace_trigger_soft_disabled(file)) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ fields_size = trace_state->event->n_u64 * sizeof(u64);
+
+ /*
+ * Avoid ring buffer recursion detection, as this event
+ * is being performed within another event.
+ */
+ trace_state->buffer = file->tr->array_buffer.buffer;
+ ring_buffer_nest_start(trace_state->buffer);
+
+ entry = trace_event_buffer_reserve(&trace_state->fbuffer, file,
+ sizeof(*entry) + fields_size);
+ if (!entry) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ trace_state->entry = entry;
+out:
+ return ret;
+}
+EXPORT_SYMBOL_GPL(synth_event_trace_start);
+
+static int save_synth_val(struct synth_field *field, u64 val,
+ struct synth_event_trace_state *trace_state)
+{
+ struct synth_trace_event *entry = trace_state->entry;
+
+ if (field->is_string) {
+ char *str_val = (char *)(long)val;
+ char *str_field;
+
+ if (!str_val)
+ return -EINVAL;
+
+ str_field = (char *)&entry->fields[field->offset];
+ strscpy(str_field, str_val, STR_VAR_LEN_MAX);
+ } else
+ entry->fields[field->offset] = val;
+
+ return 0;
+}
+
+/**
+ * synth_event_add_next_val - Add the next field's value to an open synth trace
+ * @val: The value to set the next field to
+ * @trace_state: A pointer to object tracking the piecewise trace state
+ *
+ * Set the value of the next field in an event that's been opened by
+ * synth_event_trace_start().
+ *
+ * The val param should be the value cast to u64. If the value points
+ * to a string, the val param should be a char * cast to u64.
+ *
+ * This function assumes all the fields in an event are to be set one
+ * after another - successive calls to this function are made, one for
+ * each field, in the order of the fields in the event, until all
+ * fields have been set. If you'd rather set each field individually
+ * without regard to ordering, synth_event_add_val() can be used
+ * instead.
+ *
+ * Note however that synth_event_add_next_val() and
+ * synth_event_add_val() can't be intermixed for a given event trace -
+ * one or the other but not both can be used at the same time.
+ *
+ * Note also that synth_event_trace_end() must be called after all
+ * values have been added for each event trace, regardless of whether
+ * adding all field values succeeded or not.
+ *
+ * Return: 0 on success, err otherwise.
+ */
+int synth_event_add_next_val(u64 val,
+ struct synth_event_trace_state *trace_state)
+{
+ struct synth_field *field;
+ struct synth_event *event;
+ int ret = 0;
+
+ if (!trace_state) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ /* can't mix add_next_synth_val() with add_synth_val() */
+ if (trace_state->add_name) {
+ ret = -EINVAL;
+ goto out;
+ }
+ trace_state->add_next = true;
+
+ if (!trace_state->enabled)
+ goto out;
+
+ event = trace_state->event;
+
+ if (trace_state->cur_field >= event->n_fields) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ field = event->fields[trace_state->cur_field++];
+ ret = save_synth_val(field, val, trace_state);
+ out:
+ return ret;
+}
+EXPORT_SYMBOL_GPL(synth_event_add_next_val);
+
+static struct synth_field *find_synth_field(struct synth_event *event,
+ const char *field_name)
+{
+ struct synth_field *field = NULL;
+ unsigned int i;
+
+ for (i = 0; i < event->n_fields; i++) {
+ field = event->fields[i];
+ if (strcmp(field->name, field_name) == 0)
+ return field;
+ }
+
+ return NULL;
+}
+
+/**
+ * synth_event_add_val - Add a named field's value to an open synth trace
+ * @field_name: The name of the synthetic event field value to set
+ * @val: The value to set the next field to
+ * @trace_state: A pointer to object tracking the piecewise trace state
+ *
+ * Set the value of the named field in an event that's been opened by
+ * synth_event_trace_start().
+ *
+ * The val param should be the value cast to u64. If the value points
+ * to a string, the val param should be a char * cast to u64.
+ *
+ * This function looks up the field name, and if found, sets the field
+ * to the specified value. This lookup makes this function more
+ * expensive than synth_event_add_next_val(), so use that or the
+ * none-piecewise synth_event_trace() instead if efficiency is more
+ * important.
+ *
+ * Note however that synth_event_add_next_val() and
+ * synth_event_add_val() can't be intermixed for a given event trace -
+ * one or the other but not both can be used at the same time.
+ *
+ * Note also that synth_event_trace_end() must be called after all
+ * values have been added for each event trace, regardless of whether
+ * adding all field values succeeded or not.
+ *
+ * Return: 0 on success, err otherwise.
+ */
+int synth_event_add_val(const char *field_name, u64 val,
+ struct synth_event_trace_state *trace_state)
+{
+ struct synth_trace_event *entry;
+ struct synth_event *event;
+ struct synth_field *field;
+ int ret = 0;
+
+ if (!trace_state) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ /* can't mix add_next_synth_val() with add_synth_val() */
+ if (trace_state->add_next) {
+ ret = -EINVAL;
+ goto out;
+ }
+ trace_state->add_name = true;
+
+ if (!trace_state->enabled)
+ goto out;
+
+ event = trace_state->event;
+ entry = trace_state->entry;
+
+ field = find_synth_field(event, field_name);
+ if (!field) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ ret = save_synth_val(field, val, trace_state);
+ out:
+ return ret;
+}
+EXPORT_SYMBOL_GPL(synth_event_add_val);
+
+/**
+ * synth_event_trace_end - End piecewise synthetic event trace
+ * @trace_state: A pointer to object tracking the piecewise trace state
+ *
+ * End the trace of a synthetic event opened by
+ * synth_event_trace__start().
+ *
+ * This function 'closes' an event trace, which basically means that
+ * it commits the reserved event and cleans up other loose ends.
+ *
+ * A pointer to a trace_state object is passed in, which will keep
+ * track of the current event trace state opened with
+ * synth_event_trace_start().
+ *
+ * Note that this function must be called after all values have been
+ * added for each event trace, regardless of whether adding all field
+ * values succeeded or not.
+ *
+ * Return: 0 on success, err otherwise.
+ */
+int synth_event_trace_end(struct synth_event_trace_state *trace_state)
+{
+ if (!trace_state)
+ return -EINVAL;
+
+ trace_event_buffer_commit(&trace_state->fbuffer);
+
+ ring_buffer_nest_end(trace_state->buffer);
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(synth_event_trace_end);
+
static int create_synth_event(int argc, const char **argv)
{
const char *name = argv[0];
--
2.14.1
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