Configuration and logging improvements to logrotate_fs (#1074)

### What does this PR do?

This commit involves minor tweaks to the logrotate_fs to improve logging
and the configuration of said generator. Also I include an example
config.

examples/lading-logrotatefs.yaml

@@ -0,0 +1,17 @@
+generator:
+  - file_gen:
+      logrotate_fs:
+        seed: [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53,
+               59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131]
+        concurrent_logs: 8
+        maximum_bytes_per_log: 100MB
+        total_rotations: 4
+        max_depth: 0
+        variant: "ascii"
+        bytes_per_second: 10MB
+        maximum_prebuild_cache_size_bytes: 1GB
+        mount_point: /tmp/logrotate
+
+blackhole:
+  - tcp:
+      binding_addr: "0.0.0.0:8080"

lading/src/generator/file_gen/logrotate_fs.rs

@@ -22,7 +22,7 @@ use std::{
     time::Duration,
 };
 use tokio::task::{self, JoinError};
-use tracing::{error, info};
+use tracing::{debug, error, info};
 
 mod model;
 
@@ -123,6 +123,10 @@ impl Server {
             config.concurrent_logs,
         );
 
+        info!(
+            "Creating logrotate filesystem with mount point {mount}",
+            mount = config.mount_point.display(),
+        );
         // Initialize the FUSE filesystem
         let fs = LogrotateFS {
             state: Arc::new(Mutex::new(state)),
@@ -243,7 +247,7 @@ impl Filesystem for LogrotateFS {
         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) {
-                info!("lookup: returning attr for inode {}: {:?}", ino, attr);
+                debug!("lookup: returning attr for inode {}: {:?}", ino, attr);
                 reply.entry(&TTL, &attr, 0);
                 return;
             }

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

@@ -379,9 +379,14 @@ impl State {
             return state;
         }
 
-        // Generate random group names
-        let num_groups = rng.gen_range(1..=concurrent_logs);
-        for group_id in 0..num_groups {
+        // Strategy:
+        //
+        // For 0 to `concurrent_logs` generate a directory path up to
+        // `max_depth` from the root node and place a file in that
+        // directory. Node that we must keep track of the group we're in, so we
+        // loop over `concurrent_logs`.
+        for group_id in 0..concurrent_logs {
+            // First, generate the group name.
             let base: String = (0..8)
                 .map(|_| rng.sample(rand::distributions::Alphanumeric) as char)
                 .collect();
@@ -392,17 +397,14 @@ impl State {
                 names.push(format!("{base_name}.{i}")); // Ordinal i
             }
             state.group_names.push(names);
-        }
 
-        // Strategy:
-        //
-        // For 0 to num_groups generate a directory path up to `max_depth` from
-        // the root node and place a file in that directory. Node that we must
-        // keep track of the group we're in, so we loop over num_groups.
-
-        for group_id in 0..num_groups {
+            // Now, build up the directory tree and put the file in it.
             let mut current_inode = state.root_inode;
-            let depth = rng.gen_range(1..=max_depth as usize);
+            let depth = if max_depth == 0 {
+                0
+            } else {
+                rng.gen_range(1..=max_depth as usize)
+            };
 
             // Build the directory path
             for _ in 0..depth {