scx_rustland: handle graceful vs non-graceful exit

Do not report an exit error message if it's not needed. Moreover,
distinguish between a graceful exit vs a non-graceful exit.

NOTE: in the future the whole exit handling probably can be moved to a
more generic place (scx_utils) to prevent code duplication across
schedulers and also to prevent small inconsistencies like this one.

Signed-off-by: Andrea Righi <[email protected]>

scheds/rust/scx_rustland/src/main.rs

@@ -275,15 +275,32 @@ impl<'a> Scheduler<'a> {
 
     // Called on exit to get exit code and exit message from the BPF part.
     fn report_bpf_exit_kind(&mut self) -> Result<()> {
+        // Report msg if EXT_OPS_EXIT_ERROR.
         match self.read_bpf_exit_kind() {
             0 => Ok(()),
-            etype => {
+            // etype can be one of the following (from include/linux/sched/ext.h):
+            //
+            // enum scx_exit_kind {
+            //     SCX_EXIT_NONE,
+            //     SCX_EXIT_DONE,
+            //
+            //     SCX_EXIT_UNREG = 64,    /* BPF unregistration */
+            //     SCX_EXIT_SYSRQ,         /* requested by 'S' sysrq */
+            //
+            //     SCX_EXIT_ERROR = 1024,  /* runtime error, error msg contains details */
+            //     SCX_EXIT_ERROR_BPF,     /* ERROR but triggered through scx_bpf_error() */
+            //     SCX_EXIT_ERROR_STALL,   /* watchdog detected stalled runnable tasks */
+            // };
+            etype if etype > 64 => {
                 let cstr = unsafe { CStr::from_ptr(self.skel.bss().exit_msg.as_ptr() as *const _) };
                 let msg = cstr
                     .to_str()
                     .context("Failed to convert exit msg to string")
                     .unwrap();
-                info!("BPF exit_kind={} msg={}", etype, msg);
+                bail!("BPF exit_kind={} msg={}", etype, msg);
+            }
+            etype => {
+                info!("BPF exit_kind={}", etype);
                 Ok(())
             }
         }