Reduce state cardinality from 4 to 2

Encode into the type system the fact that PerfLink::probe_kind and
PerfLink::event_alias are present or absent together.

aya/src/programs/perf_attach.rs

@@ -3,7 +3,10 @@ use std::os::fd::{AsFd as _, AsRawFd as _, OwnedFd, RawFd};
 
 use crate::{
     generated::bpf_attach_type::BPF_PERF_EVENT,
-    programs::{probe::detach_debug_fs, FdLink, Link, ProbeKind, ProgramError},
+    programs::{
+        probe::{detach_debug_fs, ProbeEvent},
+        FdLink, Link, ProgramError,
+    },
     sys::{bpf_link_create, perf_event_ioctl, SysResult},
     FEATURES, PERF_EVENT_IOC_DISABLE, PERF_EVENT_IOC_ENABLE, PERF_EVENT_IOC_SET_BPF,
 };
@@ -46,8 +49,7 @@ pub struct PerfLinkId(RawFd);
 #[derive(Debug)]
 pub struct PerfLink {
     perf_fd: OwnedFd,
-    probe_kind: Option<ProbeKind>,
-    event_alias: Option<String>,
+    event: Option<ProbeEvent>,
 }
 
 impl Link for PerfLink {
@@ -57,13 +59,11 @@ impl Link for PerfLink {
         PerfLinkId(self.perf_fd.as_raw_fd())
     }
 
-    fn detach(mut self) -> Result<(), ProgramError> {
-        let _: SysResult<_> = perf_event_ioctl(self.perf_fd.as_fd(), PERF_EVENT_IOC_DISABLE, 0);
-
-        if let Some(probe_kind) = self.probe_kind.take() {
-            if let Some(event_alias) = self.event_alias.take() {
-                let _: Result<_, _> = detach_debug_fs(probe_kind, &event_alias);
-            }
+    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);
+        if let Some(event) = event {
+            let _: Result<_, _> = detach_debug_fs(event);
         }
 
         Ok(())
@@ -80,24 +80,22 @@ pub(crate) fn perf_attach(prog_fd: RawFd, fd: OwnedFd) -> Result<PerfLinkInner,
         )? as RawFd;
         Ok(PerfLinkInner::FdLink(FdLink::new(link_fd)))
     } else {
-        perf_attach_either(prog_fd, fd, None, None)
+        perf_attach_either(prog_fd, fd, None)
     }
 }
 
 pub(crate) fn perf_attach_debugfs(
     prog_fd: RawFd,
     fd: OwnedFd,
-    probe_kind: ProbeKind,
-    event_alias: String,
+    event: ProbeEvent,
 ) -> Result<PerfLinkInner, ProgramError> {
-    perf_attach_either(prog_fd, fd, Some(probe_kind), Some(event_alias))
+    perf_attach_either(prog_fd, fd, Some(event))
 }
 
 fn perf_attach_either(
     prog_fd: RawFd,
     fd: OwnedFd,
-    probe_kind: Option<ProbeKind>,
-    event_alias: Option<String>,
+    event: Option<ProbeEvent>,
 ) -> Result<PerfLinkInner, ProgramError> {
     perf_event_ioctl(fd.as_fd(), PERF_EVENT_IOC_SET_BPF, prog_fd).map_err(|(_, io_error)| {
         ProgramError::SyscallError {
@@ -112,9 +110,5 @@ fn perf_attach_either(
         }
     })?;
 
-    Ok(PerfLinkInner::PerfLink(PerfLink {
-        perf_fd: fd,
-        probe_kind,
-        event_alias,
-    }))
+    Ok(PerfLinkInner::PerfLink(PerfLink { perf_fd: fd, event }))
 }

aya/src/programs/probe.rs

@@ -42,6 +42,12 @@ impl ProbeKind {
     }
 }
 
+#[derive(Debug)]
+pub(crate) struct ProbeEvent {
+    kind: ProbeKind,
+    event_alias: String,
+}
+
 pub(crate) fn attach<T: Link + From<PerfLinkInner>>(
     program_data: &mut ProgramData<T>,
     kind: ProbeKind,
@@ -56,8 +62,7 @@ pub(crate) fn attach<T: Link + From<PerfLinkInner>>(
         let link = T::from(perf_attach_debugfs(
             program_data.fd_or_err()?,
             fd,
-            kind,
-            event_alias,
+            ProbeEvent { kind, event_alias },
         )?);
         return program_data.links.insert(link);
     };
@@ -67,19 +72,22 @@ pub(crate) fn attach<T: Link + From<PerfLinkInner>>(
     program_data.links.insert(link)
 }
 
-pub(crate) fn detach_debug_fs(kind: ProbeKind, event_alias: &str) -> Result<(), ProgramError> {
+pub(crate) fn detach_debug_fs(event: ProbeEvent) -> Result<(), ProgramError> {
     use ProbeKind::*;
 
     let tracefs = find_tracefs_path()?;
 
-    match kind {
-        KProbe | KRetProbe => delete_probe_event(tracefs, kind, event_alias)
-            .map_err(|(filename, io_error)| KProbeError::FileError { filename, io_error })?,
-        UProbe | URetProbe => delete_probe_event(tracefs, kind, event_alias)
-            .map_err(|(filename, io_error)| UProbeError::FileError { filename, io_error })?,
-    };
+    let ProbeEvent {
+        kind,
+        event_alias: _,
+    } = &event;
+    let kind = *kind;
+    let result = delete_probe_event(tracefs, event);
 
-    Ok(())
+    result.map_err(|(filename, io_error)| match kind {
+        KProbe | KRetProbe => KProbeError::FileError { filename, io_error }.into(),
+        UProbe | URetProbe => UProbeError::FileError { filename, io_error }.into(),
+    })
 }
 
 fn create_as_probe(
@@ -196,17 +204,14 @@ fn create_probe_event(
     Ok(event_alias)
 }
 
-fn delete_probe_event(
-    tracefs: &Path,
-    kind: ProbeKind,
-    event_alias: &str,
-) -> Result<(), (String, io::Error)> {
+fn delete_probe_event(tracefs: &Path, event: ProbeEvent) -> Result<(), (String, io::Error)> {
+    let ProbeEvent { kind, event_alias } = event;
     let events_file_name = tracefs.join(format!("{}_events", kind.pmu()));
 
     let events = fs::read_to_string(&events_file_name)
         .map_err(|e| (events_file_name.display().to_string(), e))?;
 
-    let found = events.lines().any(|line| line.contains(event_alias));
+    let found = events.lines().any(|line| line.contains(&event_alias));
 
     if found {
         let mut events_file = OpenOptions::new()