From 65f51deabd83d4f97fe0146d950238316a7b4e74 Mon Sep 17 00:00:00 2001
From: Thaumy <thaumy@outlook.com>
Date: Wed, 20 Mar 2024 11:40:09 +0800
Subject: [PATCH] add helper functions for `TracepointEvent`

- `TracepointEvent::from_event_name`: construct `TracepointEvent` from event name.
- `TracepointEvent::available_event_names`: get all available event names.
---
 src/perf_event/event/tracepoint.rs | 85 ++++++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)

diff --git a/src/perf_event/event/tracepoint.rs b/src/perf_event/event/tracepoint.rs
index 6abfed5..6911ecb 100644
--- a/src/perf_event/event/tracepoint.rs
+++ b/src/perf_event/event/tracepoint.rs
@@ -13,6 +13,25 @@
 // see <https://www.gnu.org/licenses/>.
 
 use crate::perf_event::event::Event;
+use std::num::ParseIntError;
+use std::ops::Not;
+use std::path::PathBuf;
+use std::{fs, io};
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+pub enum Error {
+    #[error("Event name is invalid")]
+    InvalidEventName,
+    #[error("Event is unsupported")]
+    UnsupportedEvent,
+    #[error("Failed to find tracefs")]
+    FailedToFindTracefs,
+    #[error("Failed to parse id file: {0}")]
+    FailedToParseIdFile(ParseIntError),
+    #[error("I/O error: {0}")]
+    IoError(io::Error),
+}
 
 #[derive(Clone, Debug)]
 pub struct TracepointEvent {
@@ -24,6 +43,57 @@ impl TracepointEvent {
     pub const fn new(id: u64) -> Self {
         Self { id }
     }
+
+    /// The format of the event name is `lhs:rhs`, for example: `sched:sched_switch`
+    ///
+    /// For all available events, see: `/sys/kernel/debug/tracing/available_events`
+    pub fn from_event_name(event_name: &str) -> Result<Self, Error> {
+        let mut split = event_name.split(':');
+        let path = match (split.next(), split.next()) {
+            (_, None) => return Err(Error::InvalidEventName),
+            (None, _) => return Err(Error::InvalidEventName),
+            (Some(lhs), Some(rhs)) => {
+                let mut path = tracefs_path()?;
+                path.push("events");
+                path.push(lhs);
+                path.push(rhs);
+                path.push("id");
+                path
+            }
+        };
+
+        if path.exists().not() {
+            return Err(Error::UnsupportedEvent);
+        }
+
+        let contents = fs::read_to_string(path).map_err(Error::IoError)?;
+        let id =
+            str::parse::<u64>(&contents.replace('\n', "")).map_err(Error::FailedToParseIdFile)?;
+
+        Ok(Self { id })
+    }
+
+    /// Get all available event names from `/sys/kernel/debug/tracing/available_events`
+    pub fn available_event_names() -> Result<Vec<String>, Error> {
+        let mut path = tracefs_path()?;
+        path.push("available_events");
+
+        let contents = fs::read_to_string(path).map_err(Error::IoError)?;
+        let lines: Vec<String> = contents.lines().map(|it| it.to_string()).collect();
+
+        Ok(lines)
+    }
+}
+
+fn tracefs_path() -> Result<PathBuf, Error> {
+    let contents = fs::read_to_string("/proc/mounts").map_err(Error::IoError)?;
+
+    contents
+        .lines()
+        .find(|line| line.starts_with("tracefs"))
+        .and_then(|line| line.split(' ').nth(1))
+        .ok_or_else(|| Error::FailedToFindTracefs)
+        .map(PathBuf::from)
 }
 
 impl From<TracepointEvent> for Event {
@@ -31,3 +101,18 @@ impl From<TracepointEvent> for Event {
         Self::Tracepoint(value)
     }
 }
+
+#[test]
+fn test_from_event_name() {
+    let ev_name = "kmem:kfree";
+    let ev = TracepointEvent::from_event_name(ev_name);
+    dbg!(ev.unwrap());
+}
+
+#[test]
+fn test_available_event_names() {
+    let ev_names = TracepointEvent::available_event_names();
+    dbg!(&ev_names);
+    let ev_names = ev_names.unwrap();
+    assert!(ev_names.len() > 0);
+}