Add links iterator

This is not yet exposed in documentation, but is complete enough for use
in tests, removing the dependency on bpftool.

Updates #645.

aya/src/programs/mod.rs

@@ -104,14 +104,15 @@ pub use uprobe::{UProbe, UProbeError};
 pub use xdp::{Xdp, XdpError, XdpFlags};
 
 use crate::{
-    generated::{bpf_attach_type, bpf_prog_info, bpf_prog_type},
+    generated::{bpf_attach_type, bpf_link_info, bpf_prog_info, bpf_prog_type},
     maps::MapError,
     obj::{self, btf::BtfError, Function, VerifierLog},
     pin::PinError,
     sys::{
-        bpf_btf_get_fd_by_id, bpf_get_object, bpf_load_program, bpf_pin_object,
-        bpf_prog_get_fd_by_id, bpf_prog_get_info_by_fd, bpf_prog_query, iter_prog_ids,
-        retry_with_verifier_logs, BpfLoadProgramAttrs, SyscallError,
+        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_prog_query, iter_link_ids, iter_prog_ids, retry_with_verifier_logs,
+        BpfLoadProgramAttrs, SyscallError,
     },
     util::KernelVersion,
     VerifierLogLevel,
@@ -998,3 +999,19 @@ pub fn loaded_programs() -> impl Iterator<Item = Result<ProgramInfo, ProgramErro
         })
         .map(|result| result.map(ProgramInfo).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)]
+pub fn loaded_links() -> impl Iterator<Item = Result<bpf_link_info, ProgramError>> {
+    iter_link_ids()
+        .map(|id| {
+            let id = id?;
+            bpf_link_get_fd_by_id(id)
+        })
+        .map(|fd| {
+            let fd = fd?;
+            bpf_link_get_info_by_fd(fd.as_raw_fd())
+        })
+        .map(|result| result.map_err(Into::into))
+}

aya/src/sys/bpf.rs

@@ -508,6 +508,20 @@ pub(crate) fn bpf_map_get_info_by_fd(fd: RawFd) -> Result<bpf_map_info, SyscallE
     bpf_obj_get_info_by_fd::<bpf_map_info>(fd)
 }
 
+pub(crate) fn bpf_link_get_fd_by_id(link_id: u32) -> Result<OwnedFd, SyscallError> {
+    let mut attr = unsafe { mem::zeroed::<bpf_attr>() };
+
+    attr.__bindgen_anon_6.__bindgen_anon_1.link_id = link_id;
+    // SAFETY: BPF_LINK_GET_FD_BY_ID returns a new file descriptor.
+    unsafe { fd_sys_bpf(bpf_cmd::BPF_LINK_GET_FD_BY_ID, &mut attr) }.map_err(|(code, io_error)| {
+        assert_eq!(code, -1);
+        SyscallError {
+            call: "bpf_link_get_fd_by_id",
+            io_error,
+        }
+    })
+}
+
 pub(crate) fn bpf_link_get_info_by_fd(fd: RawFd) -> Result<bpf_link_info, SyscallError> {
     let fd = unsafe { BorrowedFd::borrow_raw(fd) };
     bpf_obj_get_info_by_fd::<bpf_link_info>(fd)
@@ -909,11 +923,15 @@ fn sys_bpf(cmd: bpf_cmd, attr: &mut bpf_attr) -> SysResult<c_long> {
     syscall(Syscall::Bpf { cmd, attr })
 }
 
-fn bpf_prog_get_next_id(id: u32) -> Result<Option<u32>, SyscallError> {
+fn bpf_obj_get_next_id(
+    id: u32,
+    cmd: bpf_cmd,
+    name: &'static str,
+) -> Result<Option<u32>, SyscallError> {
     let mut attr = unsafe { mem::zeroed::<bpf_attr>() };
     let u = unsafe { &mut attr.__bindgen_anon_6 };
     u.__bindgen_anon_1.start_id = id;
-    match sys_bpf(bpf_cmd::BPF_PROG_GET_NEXT_ID, &mut attr) {
+    match sys_bpf(cmd, &mut attr) {
         Ok(code) => {
             assert_eq!(code, 0);
             Ok(Some(unsafe { attr.__bindgen_anon_6.next_id }))
@@ -924,20 +942,23 @@ fn bpf_prog_get_next_id(id: u32) -> Result<Option<u32>, SyscallError> {
                 Ok(None)
             } else {
                 Err(SyscallError {
-                    call: "bpf_prog_get_next_id",
+                    call: name,
                     io_error,
                 })
             }
         }
     }
 }
 
-pub(crate) fn iter_prog_ids() -> impl Iterator<Item = Result<u32, SyscallError>> {
+fn iter_obj_ids(
+    cmd: bpf_cmd,
+    name: &'static str,
+) -> impl Iterator<Item = Result<u32, SyscallError>> {
     let mut current_id = Some(0);
     iter::from_fn(move || {
         let next_id = {
             let current_id = current_id?;
-            bpf_prog_get_next_id(current_id).transpose()
+            bpf_obj_get_next_id(current_id, cmd, name).transpose()
         };
         current_id = next_id.as_ref().and_then(|next_id| match next_id {
             Ok(next_id) => Some(*next_id),
@@ -947,6 +968,14 @@ pub(crate) fn iter_prog_ids() -> impl Iterator<Item = Result<u32, SyscallError>>
     })
 }
 
+pub(crate) fn iter_prog_ids() -> impl Iterator<Item = Result<u32, SyscallError>> {
+    iter_obj_ids(bpf_cmd::BPF_PROG_GET_NEXT_ID, "bpf_prog_get_next_id")
+}
+
+pub(crate) fn iter_link_ids() -> impl Iterator<Item = Result<u32, SyscallError>> {
+    iter_obj_ids(bpf_cmd::BPF_LINK_GET_NEXT_ID, "bpf_link_get_next_id")
+}
+
 pub(crate) fn retry_with_verifier_logs<T>(
     max_retries: usize,
     f: impl Fn(&mut [u8]) -> SysResult<T>,

test/README.md

@@ -11,7 +11,6 @@ To run locally all you need is:
 
 1. Rust nightly
 1. `cargo install bpf-linker`
-1. `bpftool` [^1]
 
 ### Other OSs
 
@@ -52,5 +51,3 @@ Tests should follow these guidelines:
 - You may add a new module, or use an existing one.
 - Test functions should not return `anyhow::Result<()>` since this produces errors without stack
   traces. Prefer to `panic!` instead.
-
-[^1]: TODO(https://github.com/aya-rs/aya/issues/645): Remove this dependency.