Add telemetry to logrotate_fs

This commit adds telemetry around filesystem and model operations. I am
especially interested to know when rotations happen, how often and what
operations the reader is calling against the filesystem.

Signed-off-by: Brian L. Troutwine <brian.troutwine@datadoghq.com>

lading/src/generator/file_gen/logrotate_fs.rs

@@ -10,6 +10,7 @@ use fuser::{
     ReplyDirectory, ReplyEntry, Request,
 };
 use lading_payload::block;
+use metrics::counter;
 use nix::libc::{self, ENOENT};
 use rand::{rngs::SmallRng, SeedableRng};
 use serde::{Deserialize, Serialize};
@@ -250,6 +251,8 @@ impl Filesystem for LogrotateFS {
         let mut state = self.state.lock().expect("lock poisoned");
         state.advance_time(tick);
 
+        counter!("fs_lookup").increment(1);
+
         let name_str = name.to_str().unwrap_or("");
         if let Some(ino) = state.lookup(tick, parent as usize, name_str) {
             if let Some(attr) = getattr_helper(&mut state, self.start_time_system, tick, ino) {
@@ -270,6 +273,8 @@ impl Filesystem for LogrotateFS {
         let mut state = self.state.lock().expect("lock poisoned");
         state.advance_time(tick);
 
+        counter!("fs_getattr").increment(1);
+
         if let Some(attr) = getattr_helper(&mut state, self.start_time_system, tick, ino as usize) {
             reply.attr(&TTL, &attr);
         } else {
@@ -293,6 +298,8 @@ impl Filesystem for LogrotateFS {
         let mut state = self.state.lock().expect("lock poisoned");
         state.advance_time(tick);
 
+        counter!("fs_read").increment(1);
+
         // Get the FileHandle from fh
         let file_handle = {
             let open_files = self.open_files.lock().expect("lock poisoned");
@@ -329,6 +336,8 @@ impl Filesystem for LogrotateFS {
         let mut state = self.state.lock().expect("lock poisoned");
         state.advance_time(tick);
 
+        counter!("fs_release").increment(1);
+
         // Remove the FileHandle from the mapping
         let file_handle = {
             let mut open_files = self.open_files.lock().expect("lock poisoned");
@@ -350,6 +359,8 @@ impl Filesystem for LogrotateFS {
         let mut state = self.state.lock().expect("lock poisoned");
         state.advance_time(tick);
 
+        counter!("fs_readdir").increment(1);
+
         let root_inode = state.root_inode();
         let mut entry_offset = 0;
 
@@ -410,6 +421,8 @@ impl Filesystem for LogrotateFS {
         let mut state = self.state.lock().expect("lock poisoned");
         state.advance_time(tick);
 
+        counter!("fs_open").increment(1);
+
         if let Some(file_handle) = state.open_file(tick, ino as usize) {
             let fh = file_handle.id();
             {

lading/src/generator/file_gen/logrotate_fs/model.rs

@@ -642,6 +642,7 @@ impl State {
                 let (remove_current, next_peer) = match node {
                     Node::File { file } => {
                         file.incr_ordinal();
+                        counter!("log_file_rotated").increment(1);
 
                         let remove_current = file.ordinal() > self.max_rotations;
                         (remove_current, file.peer)
@@ -712,6 +713,7 @@ impl State {
         for inode in to_remove {
             if let Some(Node::File { file }) = self.nodes.remove(&inode) {
                 let lost_bytes = file.bytes_written.saturating_sub(file.max_offset_observed);
+                counter!("log_file_deleted").increment(1);
                 counter!("lost_bytes").increment(lost_bytes);
             }
         }