Revert "scx_rustland_core: use new consume_raw() libbpf-rs API"

In order to use the new consume_raw() API we need to depend on a version
of libbpf-rs that is not released yet.

Apparently adding such dependency may introduce a potential dependency
conflict with libbpf-sys.

Therefore, revert this change and go back to the previous consume() API.
One a new version of libbpf-rs will be out we can update all our
dependencies to use the new libbpf-rs and re-apply this patch to
scx_rustland_core.

Fixes: 7c8c5fd ("scx_rustland_core: use new consume_raw() libbpf-rs API")
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>

rust/scx_rustland_core/Cargo.toml

@@ -15,7 +15,7 @@ include = [
 
 [dependencies]
 anyhow = "1.0"
-libbpf-rs = { git = "https://github.com/libbpf/libbpf-rs.git#af3296c00d74fd50b311adc7f931563be137cd8b" }
+libbpf-rs = "0.22.0"
 libc = "0.2.137"
 buddy-alloc = "0.5.1"
 scx_utils = { path = "../scx_utils", version = "0.6" }

rust/scx_rustland_core/src/bpf.rs

@@ -172,10 +172,6 @@ struct AlignedBuffer([u8; BUFSIZE]);
 
 static mut BUF: AlignedBuffer = AlignedBuffer([0; BUFSIZE]);
 
-// Special negative error code for libbpf to stop after consuming just one item from a BPF
-// ring buffer.
-const LIBBPF_STOP: i32 = -255;
-
 impl<'cb> BpfScheduler<'cb> {
     pub fn init(
         slice_us: u64,
@@ -225,7 +221,7 @@ impl<'cb> BpfScheduler<'cb> {
             // Maybe we should fix this to stop processing items from the ring buffer also when a
             // value > 0 is returned.
             //
-            LIBBPF_STOP
+            -255
         }
 
         // Initialize online CPUs counter.
@@ -376,16 +372,15 @@ impl<'cb> BpfScheduler<'cb> {
     // Receive a task to be scheduled from the BPF dispatcher.
     //
     // NOTE: if task.cpu is negative the task is exiting and it does not require to be scheduled.
-    pub fn dequeue_task(&mut self) -> Result<Option<QueuedTask>, i32> {
-        match self.queued.consume_raw() {
-            0 => Ok(None),
-            LIBBPF_STOP => {
+    pub fn dequeue_task(&mut self) -> Result<Option<QueuedTask>, libbpf_rs::Error> {
+        match self.queued.consume() {
+            Ok(()) => Ok(None),
+            Err(error) if error.kind() == libbpf_rs::ErrorKind::Other => {
                 // A valid task is received, convert data to a proper task struct.
                 let task = unsafe { EnqueuedMessage::from_bytes(&BUF.0).to_queued_task() };
                 Ok(Some(task))
             }
-            res if res < 0 => Err(res),
-            res => panic!("Unexpected return value from libbpf-rs::consume_raw(): {}", res),
+            Err(error) => Err(error),
         }
     }
 

scheds/rust/scx_rlfifo/Cargo.toml

@@ -9,7 +9,7 @@ license = "GPL-2.0-only"
 [dependencies]
 anyhow = "1.0.65"
 ctrlc = { version = "3.1", features = ["termination"] }
-libbpf-rs = { git = "https://github.com/libbpf/libbpf-rs.git#af3296c00d74fd50b311adc7f931563be137cd8b" }
+libbpf-rs = "0.22.0"
 libc = "0.2.137"
 scx_utils = { path = "../../../rust/scx_utils", version = "0.6" }
 scx_rustland_core = { path = "../../../rust/scx_rustland_core", version = "0.1" }

scheds/rust/scx_rustland/Cargo.toml

@@ -11,7 +11,7 @@ anyhow = "1.0.65"
 clap = { version = "4.1", features = ["derive", "env", "unicode", "wrap_help"] }
 ctrlc = { version = "3.1", features = ["termination"] }
 fb_procfs = "0.7.0"
-libbpf-rs = { git = "https://github.com/libbpf/libbpf-rs.git#af3296c00d74fd50b311adc7f931563be137cd8b" }
+libbpf-rs = "0.22.0"
 libc = "0.2.137"
 log = "0.4.17"
 ordered-float = "3.4.0"