Add the ability to detach an eBPF program

Our user-space software agent has, until now, relied on catching the `SIGINT`
signal (i.e. Ctl+C) for the application to know when to exit.  Exiting causes
handles in Rust to go out of scope, which invokes `Drop` handlers and unloads
eBPF programs and maps from the kernel.  However, if any unhandled signal were
to cause the application to exit un-gracefully, `Drop` handlers would not be
invoked, and eBPF resources would remain loaded in the kernel.  The number of
loaded programs would build up over time as the application is restarted.

Gracefully handling more types of signals is a good approach, but is best
effort.  If the drop logic were to fail, or an unhandle-able signal were
received, resources would be left behind.  A robust approach is to perform
cleanup on application startup, where previously loaded eBPF programs are
identified and unloaded from the kernel.

To support that effort, this change adds the a public `detach_program()`
function, which wraps the internal `bpf_prog_detach()`.

aya/src/programs/mod.rs

@@ -122,9 +122,9 @@ use crate::{
     },
     sys::{
         bpf_btf_get_fd_by_id, bpf_get_object, bpf_link_get_fd_by_id, bpf_link_get_info_by_fd,
-        bpf_load_program, bpf_pin_object, bpf_prog_get_fd_by_id, bpf_prog_get_info_by_fd,
+        bpf_load_program, bpf_pin_object, bpf_prog_detach, bpf_prog_get_fd_by_id,
-        bpf_prog_query, iter_link_ids, iter_prog_ids, retry_with_verifier_logs,
+        bpf_prog_get_info_by_fd, bpf_prog_query, iter_link_ids, iter_prog_ids,
-        EbpfLoadProgramAttrs, SyscallError,
+        retry_with_verifier_logs, EbpfLoadProgramAttrs, SyscallError,
     },
     util::{bytes_of_bpf_name, KernelVersion},
     VerifierLogLevel,
@@ -1151,6 +1151,15 @@ pub fn loaded_programs() -> impl Iterator<Item = Result<ProgramInfo, ProgramErro
         .map(|result| result.map(ProgramInfo).map_err(Into::into))
 }
 
+/// Detaches the given program, unloading it from the kernel.
+pub fn detach_program(
+    prog_fd: BorrowedFd<'_>,
+    target_fd: BorrowedFd<'_>,
+    attach_type: bpf_attach_type,
+) -> Result<(), ProgramError> {
+    bpf_prog_detach(prog_fd, target_fd, attach_type).map_err(Into::into)
+}
+
 // TODO(https://github.com/aya-rs/aya/issues/645): this API is currently used in tests. Stabilize
 // and remove doc(hidden).
 #[doc(hidden)]