Use O_APPEND for logs and log version number

In background mode we have two processes both racing on the log file,
and they can scribble each other's log entries (I saw this in awslabs#566).
O_APPEND should fix that. We should also log the version number as a
point of reference.

Signed-off-by: James Bornholt <[email protected]>

mountpoint-s3/src/logging.rs

@@ -102,7 +102,7 @@ fn init_tracing_subscriber(config: LoggingConfig) -> anyhow::Result<()> {
         let mut dir_builder = DirBuilder::new();
         dir_builder.recursive(true).mode(0o750);
         let mut file_options = OpenOptions::new();
-        file_options.mode(0o640).write(true).create(true);
+        file_options.mode(0o640).append(true).create(true);
 
         dir_builder.create(path).context("failed to create log folder")?;
         let file = file_options

mountpoint-s3/src/main.rs

@@ -420,6 +420,8 @@ fn main() -> anyhow::Result<()> {
 fn mount(args: CliArgs) -> anyhow::Result<FuseSession> {
     const DEFAULT_TARGET_THROUGHPUT: f64 = 10.0;
 
+    tracing::info!("mount-s3 {}", build_info::FULL_VERSION);
+
     validate_mount_point(&args.mount_point)?;
 
     let bucket_description = args.bucket_description();