aya: encode perf_event_open(2) contract

Per man 2 perf_event_open:

> RETURN VALUE
>   On success, perf_event_open() returns the new file descriptor.  On
>   error, -1 is returned and errno is set to indicate the error.

Bake this into our syscalls so we stop using `_` so much which can hide
information loss. Remove the type parameter to SysResult.

aya/src/maps/bloom_filter.rs

@@ -83,7 +83,7 @@ impl<T: BorrowMut<MapData>, V: Pod> BloomFilter<T, V> {
 
 #[cfg(test)]
 mod tests {
-    use std::{ffi::c_long, io};
+    use std::io;
 
     use assert_matches::assert_matches;
     use aya_obj::generated::{
@@ -105,7 +105,7 @@ mod tests {
         test_utils::new_obj_map::<u32>(BPF_MAP_TYPE_BLOOM_FILTER)
     }
 
-    fn sys_error(value: i32) -> SysResult<c_long> {
+    fn sys_error(value: i32) -> SysResult {
         Err((-1, io::Error::from_raw_os_error(value)))
     }
 

aya/src/maps/hash_map/hash_map.rs

@@ -103,7 +103,7 @@ impl<T: Borrow<MapData>, K: Pod, V: Pod> IterableMap<K, V> for HashMap<T, K, V>
 
 #[cfg(test)]
 mod tests {
-    use std::{ffi::c_long, io};
+    use std::io;
 
     use assert_matches::assert_matches;
     use aya_obj::generated::{
@@ -125,7 +125,7 @@ mod tests {
         test_utils::new_obj_map::<u32>(BPF_MAP_TYPE_HASH)
     }
 
-    fn sys_error(value: i32) -> SysResult<c_long> {
+    fn sys_error(value: i32) -> SysResult {
         Err((-1, io::Error::from_raw_os_error(value)))
     }
 
@@ -306,13 +306,13 @@ mod tests {
         }
     }
 
-    fn set_next_key<T: Copy>(attr: &bpf_attr, next: T) -> SysResult<c_long> {
+    fn set_next_key<T: Copy>(attr: &bpf_attr, next: T) -> SysResult {
         let key = unsafe { attr.__bindgen_anon_2.__bindgen_anon_1.next_key } as *const T as *mut T;
         unsafe { *key = next };
         Ok(0)
     }
 
-    fn set_ret<T: Copy>(attr: &bpf_attr, ret: T) -> SysResult<c_long> {
+    fn set_ret<T: Copy>(attr: &bpf_attr, ret: T) -> SysResult {
         let value = unsafe { attr.__bindgen_anon_2.__bindgen_anon_1.value } as *const T as *mut T;
         unsafe { *value = ret };
         Ok(0)
@@ -333,7 +333,7 @@ mod tests {
         assert_matches!(keys, Ok(ks) if ks.is_empty())
     }
 
-    fn get_next_key(attr: &bpf_attr) -> SysResult<c_long> {
+    fn get_next_key(attr: &bpf_attr) -> SysResult {
         match bpf_key(attr) {
             None => set_next_key(attr, 10),
             Some(10) => set_next_key(attr, 20),
@@ -343,7 +343,7 @@ mod tests {
         }
     }
 
-    fn lookup_elem(attr: &bpf_attr) -> SysResult<c_long> {
+    fn lookup_elem(attr: &bpf_attr) -> SysResult {
         match bpf_key(attr) {
             Some(10) => set_ret(attr, 100),
             Some(20) => set_ret(attr, 200),

aya/src/maps/hash_map/per_cpu_hash_map.rs

@@ -149,7 +149,7 @@ impl<T: Borrow<MapData>, K: Pod, V: Pod> IterableMap<K, PerCpuValues<V>>
 
 #[cfg(test)]
 mod tests {
-    use std::{ffi::c_long, io};
+    use std::io;
 
     use assert_matches::assert_matches;
     use aya_obj::generated::bpf_map_type::{
@@ -163,7 +163,7 @@ mod tests {
         sys::{override_syscall, SysResult},
     };
 
-    fn sys_error(value: i32) -> SysResult<c_long> {
+    fn sys_error(value: i32) -> SysResult {
         Err((-1, io::Error::from_raw_os_error(value)))
     }
 

aya/src/maps/lpm_trie.rs

@@ -190,7 +190,7 @@ impl<T: Borrow<MapData>, K: Pod, V: Pod> IterableMap<Key<K>, V> for LpmTrie<T, K
 
 #[cfg(test)]
 mod tests {
-    use std::{ffi::c_long, io, net::Ipv4Addr};
+    use std::{io, net::Ipv4Addr};
 
     use assert_matches::assert_matches;
     use aya_obj::generated::{
@@ -212,7 +212,7 @@ mod tests {
         test_utils::new_obj_map::<Key<u32>>(BPF_MAP_TYPE_LPM_TRIE)
     }
 
-    fn sys_error(value: i32) -> SysResult<c_long> {
+    fn sys_error(value: i32) -> SysResult {
         Err((-1, io::Error::from_raw_os_error(value)))
     }
 

aya/src/maps/perf/perf_buffer.rs

@@ -102,7 +102,7 @@ impl PerfBuffer {
         }
 
         let fd = perf_event_open_bpf(cpu_id as i32)
-            .map_err(|(_, io_error)| PerfBufferError::OpenError { io_error })?;
+            .map_err(|io_error| PerfBufferError::OpenError { io_error })?;
         let size = page_size * page_count;
         let mmap = MMap::new(
             fd.as_fd(),
@@ -260,7 +260,7 @@ impl AsFd for PerfBuffer {
 
 impl Drop for PerfBuffer {
     fn drop(&mut self) {
-        let _: SysResult<_> = perf_event_ioctl(self.fd.as_fd(), PERF_EVENT_IOC_DISABLE, 0);
+        let _: SysResult = perf_event_ioctl(self.fd.as_fd(), PERF_EVENT_IOC_DISABLE, 0);
     }
 }
 

aya/src/programs/perf_attach.rs

@@ -71,7 +71,7 @@ impl Link for PerfLink {
 
     fn detach(self) -> Result<(), ProgramError> {
         let Self { perf_fd, event } = self;
-        let _: SysResult<_> = perf_event_ioctl(perf_fd.as_fd(), PERF_EVENT_IOC_DISABLE, 0);
+        let _: SysResult = perf_event_ioctl(perf_fd.as_fd(), PERF_EVENT_IOC_DISABLE, 0);
         if let Some(event) = event {
             let _: Result<_, _> = detach_debug_fs(event);
         }

aya/src/programs/perf_event.rs

@@ -176,7 +176,7 @@ impl PerfEvent {
             inherit,
             0,
         )
-        .map_err(|(_code, io_error)| SyscallError {
+        .map_err(|io_error| SyscallError {
             call: "perf_event_open",
             io_error,
         })?;

aya/src/programs/probe.rs

@@ -177,7 +177,7 @@ fn create_as_probe(
     };
 
     perf_event_open_probe(perf_ty, ret_bit, fn_name, offset, pid)
-        .map_err(|(_code, io_error)| SyscallError {
+        .map_err(|io_error| SyscallError {
             call: "perf_event_open",
             io_error,
         })
@@ -203,7 +203,7 @@ fn create_as_trace_point(
 
     let category = format!("{}s", kind.pmu());
     let tpid = read_sys_fs_trace_point_id(tracefs, &category, event_alias.as_ref())?;
-    let fd = perf_event_open_trace_point(tpid, pid).map_err(|(_code, io_error)| SyscallError {
+    let fd = perf_event_open_trace_point(tpid, pid).map_err(|io_error| SyscallError {
         call: "perf_event_open",
         io_error,
     })?;

aya/src/programs/trace_point.rs

@@ -76,11 +76,10 @@ impl TracePoint {
         let prog_fd = prog_fd.as_fd();
         let tracefs = find_tracefs_path()?;
         let id = read_sys_fs_trace_point_id(tracefs, category, name.as_ref())?;
-        let fd =
-            perf_event_open_trace_point(id, None).map_err(|(_code, io_error)| SyscallError {
-                call: "perf_event_open_trace_point",
-                io_error,
-            })?;
+        let fd = perf_event_open_trace_point(id, None).map_err(|io_error| SyscallError {
+            call: "perf_event_open_trace_point",
+            io_error,
+        })?;
 
         let link = perf_attach(prog_fd, fd, None /* cookie */)?;
         self.data.links.insert(TracePointLink::new(link))

aya/src/sys/fake.rs

@@ -1,12 +1,8 @@
-use std::{
-    cell::RefCell,
-    ffi::{c_long, c_void},
-    io, ptr,
-};
+use std::{cell::RefCell, ffi::c_void, io, ptr};
 
 use super::{SysResult, Syscall};
 
-type SyscallFn = unsafe fn(Syscall<'_>) -> SysResult<c_long>;
+type SyscallFn = unsafe fn(Syscall<'_>) -> SysResult;
 
 #[cfg(test)]
 thread_local! {
@@ -15,11 +11,11 @@ thread_local! {
 }
 
 #[cfg(test)]
-unsafe fn test_syscall(_call: Syscall<'_>) -> SysResult<c_long> {
+unsafe fn test_syscall(_call: Syscall<'_>) -> SysResult {
     Err((-1, io::Error::from_raw_os_error(libc::EINVAL)))
 }
 
 #[cfg(test)]
-pub(crate) fn override_syscall(call: unsafe fn(Syscall<'_>) -> SysResult<c_long>) {
+pub(crate) fn override_syscall(call: unsafe fn(Syscall<'_>) -> SysResult) {
     TEST_SYSCALL.with(|test_impl| *test_impl.borrow_mut() = call);
 }

aya/src/sys/mod.rs

@@ -24,7 +24,7 @@ pub(crate) use netlink::*;
 pub(crate) use perf_event::*;
 use thiserror::Error;
 
-pub(crate) type SysResult<T> = Result<T, (c_long, io::Error)>;
+pub(crate) type SysResult = Result<c_long, (c_long, io::Error)>;
 
 pub(crate) enum Syscall<'a> {
     Ebpf {
@@ -88,7 +88,7 @@ impl std::fmt::Debug for Syscall<'_> {
     }
 }
 
-fn syscall(call: Syscall<'_>) -> SysResult<c_long> {
+fn syscall(call: Syscall<'_>) -> SysResult {
     #[cfg(test)]
     return TEST_SYSCALL.with(|test_impl| unsafe { test_impl.borrow()(call) });
 

aya/src/sys/perf_event.rs

@@ -1,5 +1,5 @@
 use std::{
-    ffi::{c_int, c_long, CString, OsStr},
+    ffi::{c_int, CString, OsStr},
     io, mem,
     os::fd::{BorrowedFd, FromRawFd as _},
 };
@@ -26,7 +26,7 @@ pub(crate) fn perf_event_open(
     wakeup: bool,
     inherit: bool,
     flags: u32,
-) -> SysResult<crate::MockableFd> {
+) -> io::Result<crate::MockableFd> {
     let mut attr = unsafe { mem::zeroed::<perf_event_attr>() };
 
     attr.config = config;
@@ -46,7 +46,7 @@ pub(crate) fn perf_event_open(
     perf_event_sys(attr, pid, cpu, flags)
 }
 
-pub(crate) fn perf_event_open_bpf(cpu: c_int) -> SysResult<crate::MockableFd> {
+pub(crate) fn perf_event_open_bpf(cpu: c_int) -> io::Result<crate::MockableFd> {
     perf_event_open(
         PERF_TYPE_SOFTWARE as u32,
         PERF_COUNT_SW_BPF_OUTPUT as u64,
@@ -66,7 +66,7 @@ pub(crate) fn perf_event_open_probe(
     name: &OsStr,
     offset: u64,
     pid: Option<pid_t>,
-) -> SysResult<crate::MockableFd> {
+) -> io::Result<crate::MockableFd> {
     use std::os::unix::ffi::OsStrExt as _;
 
     let mut attr = unsafe { mem::zeroed::<perf_event_attr>() };
@@ -91,7 +91,7 @@ pub(crate) fn perf_event_open_probe(
 pub(crate) fn perf_event_open_trace_point(
     id: u32,
     pid: Option<pid_t>,
-) -> SysResult<crate::MockableFd> {
+) -> io::Result<crate::MockableFd> {
     let mut attr = unsafe { mem::zeroed::<perf_event_attr>() };
 
     attr.size = mem::size_of::<perf_event_attr>() as u32;
@@ -104,7 +104,7 @@ pub(crate) fn perf_event_open_trace_point(
     perf_event_sys(attr, pid, cpu, PERF_FLAG_FD_CLOEXEC)
 }
 
-pub(crate) fn perf_event_ioctl(fd: BorrowedFd<'_>, request: u32, arg: c_int) -> SysResult<c_long> {
+pub(crate) fn perf_event_ioctl(fd: BorrowedFd<'_>, request: u32, arg: c_int) -> SysResult {
     let call = Syscall::PerfEventIoctl { fd, request, arg };
     #[cfg(not(test))]
     return syscall(call);
@@ -118,22 +118,23 @@ fn perf_event_sys(
     pid: pid_t,
     cpu: i32,
     flags: u32,
-) -> SysResult<crate::MockableFd> {
+) -> io::Result<crate::MockableFd> {
     let fd = syscall(Syscall::PerfEventOpen {
         attr,
         pid,
         cpu,
         group: -1,
         flags,
+    })
+    .map_err(|(code, io_error)| {
+        assert_eq!(code, -1);
+        io_error
     })?;
 
     let fd = fd.try_into().map_err(|std::num::TryFromIntError { .. }| {
-        (
-            fd,
-            io::Error::new(
-                io::ErrorKind::InvalidData,
-                format!("perf_event_open: invalid fd returned: {fd}"),
-            ),
+        io::Error::new(
+            io::ErrorKind::InvalidData,
+            format!("perf_event_open: invalid fd returned: {fd}"),
         )
     })?;