tracing: Add kprobe event command generation functions

Add functions used to generate kprobe event commands, built on top of
the dynevent_cmd interface.

kprobe_event_gen_cmd_start() is used to create a kprobe event command
using a variable arg list, and kretprobe_event_gen_cmd_start() does
the same for kretprobe event commands.  kprobe_event_add_fields() can
be used to add single fields one by one or as a group.  Once all
desired fields are added, kprobe_event_gen_cmd_end() or
kretprobe_event_gen_cmd_end() respectively are used to actually
execute the command and create the event.

Link: http://lkml.kernel.org/r/95cc4696502bb6017f9126f306a45ad19b4cc14f.1580323897.git.zanussi@kernel.org

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

include/linux/trace_events.h

@@ -358,6 +358,7 @@ extern void trace_put_event_file(struct trace_event_file *file);
 
 enum dynevent_type {
  DYNEVENT_TYPE_SYNTH = 1,
+ DYNEVENT_TYPE_KPROBE,
  DYNEVENT_TYPE_NONE,
 };
 
@@ -442,6 +443,36 @@ 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);
 
+extern int kprobe_event_delete(const char *name);
+
+extern void kprobe_event_cmd_init(struct dynevent_cmd *cmd,
+ char *buf, int maxlen);
+
+#define kprobe_event_gen_cmd_start(cmd, name, loc, ...) \
+ __kprobe_event_gen_cmd_start(cmd, false, name, loc, ## __VA_ARGS__, NULL)
+
+#define kretprobe_event_gen_cmd_start(cmd, name, loc, ...) \
+ __kprobe_event_gen_cmd_start(cmd, true, name, loc, ## __VA_ARGS__, NULL)
+
+extern int __kprobe_event_gen_cmd_start(struct dynevent_cmd *cmd,
+ bool kretprobe,
+ const char *name,
+ const char *loc, ...);
+
+#define kprobe_event_add_fields(cmd, ...) \
+ __kprobe_event_add_fields(cmd, ## __VA_ARGS__, NULL)
+
+#define kprobe_event_add_field(cmd, field) \
+ __kprobe_event_add_fields(cmd, field, NULL)
+
+extern int __kprobe_event_add_fields(struct dynevent_cmd *cmd, ...);
+
+#define kprobe_event_gen_cmd_end(cmd) \
+ dynevent_create(cmd)
+
+#define kretprobe_event_gen_cmd_end(cmd) \
+ dynevent_create(cmd)
+
 /*
  * Event file flags:
  * ENABLED - The event is enabled

kernel/trace/trace_kprobe.c

@@ -906,6 +906,167 @@ int trace_kprobe_run_command(const char *command)
  return trace_run_command(command, create_or_delete_trace_kprobe);
 }
 
+static int trace_kprobe_run_cmd(struct dynevent_cmd *cmd)
+{
+ return trace_run_command(cmd->buf, create_or_delete_trace_kprobe);
+}
+
+/**
+ * kprobe_event_cmd_init - Initialize a kprobe event command object
+ * @cmd: A pointer to the dynevent_cmd struct representing the new event
+ * @buf: A pointer to the buffer used to build the command
+ * @maxlen: The length of the buffer passed in @buf
+ *
+ * Initialize a synthetic event command object. Use this before
+ * calling any of the other kprobe_event functions.
+ */
+void kprobe_event_cmd_init(struct dynevent_cmd *cmd, char *buf, int maxlen)
+{
+ dynevent_cmd_init(cmd, buf, maxlen, DYNEVENT_TYPE_KPROBE,
+ trace_kprobe_run_cmd);
+}
+EXPORT_SYMBOL_GPL(kprobe_event_cmd_init);
+
+/**
+ * __kprobe_event_gen_cmd_start - Generate a kprobe event command from arg list
+ * @cmd: A pointer to the dynevent_cmd struct representing the new event
+ * @name: The name of the kprobe event
+ * @loc: The location of the kprobe event
+ * @kretprobe: Is this a return probe?
+ * @args: Variable number of arg (pairs), one pair for each field
+ *
+ * NOTE: Users normally won't want to call this function directly, but
+ * rather use the kprobe_event_gen_cmd_start() wrapper, which automatically
+ * adds a NULL to the end of the arg list. If this function is used
+ * directly, make sure the last arg in the variable arg list is NULL.
+ *
+ * Generate a kprobe event command to be executed by
+ * kprobe_event_gen_cmd_end(). This function can be used to generate the
+ * complete command or only the first part of it; in the latter case,
+ * kprobe_event_add_fields() can be used to add more fields following this.
+ *
+ * Return: 0 if successful, error otherwise.
+ */
+int __kprobe_event_gen_cmd_start(struct dynevent_cmd *cmd, bool kretprobe,
+ const char *name, const char *loc, ...)
+{
+ char buf[MAX_EVENT_NAME_LEN];
+ struct dynevent_arg arg;
+ va_list args;
+ int ret;
+
+ if (cmd->type != DYNEVENT_TYPE_KPROBE)
+ return -EINVAL;
+
+ if (kretprobe)
+ snprintf(buf, MAX_EVENT_NAME_LEN, "r:kprobes/%s", name);
+ else
+ snprintf(buf, MAX_EVENT_NAME_LEN, "p:kprobes/%s", name);
+
+ ret = dynevent_str_add(cmd, buf);
+ if (ret)
+ return ret;
+
+ dynevent_arg_init(&arg, NULL, 0);
+ arg.str = loc;
+ ret = dynevent_arg_add(cmd, &arg);
+ if (ret)
+ return ret;
+
+ va_start(args, loc);
+ for (;;) {
+ const char *field;
+
+ field = va_arg(args, const char *);
+ if (!field)
+ break;
+
+ if (++cmd->n_fields > MAX_TRACE_ARGS) {
+ ret = -EINVAL;
+ break;
+ }
+
+ arg.str = field;
+ ret = dynevent_arg_add(cmd, &arg);
+ if (ret)
+ break;
+ }
+ va_end(args);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(__kprobe_event_gen_cmd_start);
+
+/**
+ * __kprobe_event_add_fields - Add probe fields to a kprobe command from arg list
+ * @cmd: A pointer to the dynevent_cmd struct representing the new event
+ * @args: Variable number of arg (pairs), one pair for each field
+ *
+ * NOTE: Users normally won't want to call this function directly, but
+ * rather use the kprobe_event_add_fields() wrapper, which
+ * automatically adds a NULL to the end of the arg list. If this
+ * function is used directly, make sure the last arg in the variable
+ * arg list is NULL.
+ *
+ * Add probe fields to an existing kprobe command using a variable
+ * list of args. Fields are added in the same order they're listed.
+ *
+ * Return: 0 if successful, error otherwise.
+ */
+int __kprobe_event_add_fields(struct dynevent_cmd *cmd, ...)
+{
+ struct dynevent_arg arg;
+ va_list args;
+ int ret;
+
+ if (cmd->type != DYNEVENT_TYPE_KPROBE)
+ return -EINVAL;
+
+ dynevent_arg_init(&arg, NULL, 0);
+
+ va_start(args, cmd);
+ for (;;) {
+ const char *field;
+
+ field = va_arg(args, const char *);
+ if (!field)
+ break;
+
+ if (++cmd->n_fields > MAX_TRACE_ARGS) {
+ ret = -EINVAL;
+ break;
+ }
+
+ arg.str = field;
+ ret = dynevent_arg_add(cmd, &arg);
+ if (ret)
+ break;
+ }
+ va_end(args);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(__kprobe_event_add_fields);
+
+/**
+ * kprobe_event_delete - Delete a kprobe event
+ * @name: The name of the kprobe event to delete
+ *
+ * Delete a kprobe event with the give @name from kernel code rather
+ * than directly from the command line.
+ *
+ * Return: 0 if successful, error otherwise.
+ */
+int kprobe_event_delete(const char *name)
+{
+ char buf[MAX_EVENT_NAME_LEN];
+
+ snprintf(buf, MAX_EVENT_NAME_LEN, "-:%s", name);
+
+ return trace_run_command(buf, create_or_delete_trace_kprobe);
+}
+EXPORT_SYMBOL_GPL(kprobe_event_delete);
+
 static int trace_kprobe_release(struct dyn_event *ev)
 {
  struct trace_kprobe *tk = to_trace_kprobe(ev);