sys: refactor btf_obj_get_info_by_fd to share code

aya/src/programs/extension.rs

@@ -159,36 +159,23 @@ fn get_btf_info(prog_fd: i32, func_name: &str) -> Result<(RawFd, u32), ProgramEr
     }
 
     // the bpf fd of the BTF object
-    let btf_fd = sys::bpf_btf_get_fd_by_id(info.btf_id).map_err(|io_error| SyscallError {
+    let btf_fd = sys::bpf_btf_get_fd_by_id(info.btf_id)?;
-        call: "bpf_btf_get_fd_by_id",
-        io_error,
-    })?;
 
     // we need to read the btf bytes into a buffer but we don't know the size ahead of time.
     // assume 4kb. if this is too small we can resize based on the size obtained in the response.
     let mut buf = vec![0u8; 4096];
-    let btf_info = match sys::btf_obj_get_info_by_fd(btf_fd, &buf) {
+    loop {
-        Ok(info) => {
+        let info = sys::btf_obj_get_info_by_fd(btf_fd, &mut buf)?;
-            if info.btf_size > buf.len() as u32 {
+        let btf_size = info.btf_size as usize;
-                buf.resize(info.btf_size as usize, 0u8);
+        if btf_size > buf.len() {
-                let btf_info =
+            buf.resize(btf_size, 0u8);
-                    sys::btf_obj_get_info_by_fd(btf_fd, &buf).map_err(|io_error| SyscallError {
+            continue;
-                        call: "bpf_prog_get_info_by_fd",
-                        io_error,
-                    })?;
-                Ok(btf_info)
-            } else {
-                Ok(info)
         }
+        buf.truncate(btf_size);
+        break;
     }
-        Err(io_error) => Err(SyscallError {
-            call: "bpf_prog_get_info_by_fd",
-            io_error,
-        }),
-    }?;
 
-    let btf = Btf::parse(&buf[0..btf_info.btf_size as usize], Endianness::default())
+    let btf = Btf::parse(&buf, Endianness::default()).map_err(ProgramError::Btf)?;
-        .map_err(ProgramError::Btf)?;
 
     let btf_id = btf
         .id_by_type_name_kind(func_name, BtfKind::Func)

aya/src/sys/bpf.rs

@@ -539,22 +539,14 @@ pub(crate) fn bpf_link_get_info_by_fd(fd: BorrowedFd<'_>) -> Result<bpf_link_inf
 }
 
 pub(crate) fn btf_obj_get_info_by_fd(
-    prog_fd: RawFd,
+    fd: RawFd,
-    buf: &[u8],
+    buf: &mut [u8],
-) -> Result<bpf_btf_info, io::Error> {
+) -> Result<bpf_btf_info, SyscallError> {
-    let mut attr = unsafe { mem::zeroed::<bpf_attr>() };
+    let fd = unsafe { BorrowedFd::borrow_raw(fd) };
-    let mut info = unsafe { mem::zeroed::<bpf_btf_info>() };
+    bpf_obj_get_info_by_fd(fd, |info: &mut bpf_btf_info| {
-    let buf_size = buf.len() as u32;
+        info.btf = buf.as_mut_ptr() as _;
-    info.btf = buf.as_ptr() as u64;
+        info.btf_size = buf.len() as _;
-    info.btf_size = buf_size;
+    })
-    attr.info.bpf_fd = prog_fd as u32;
-    attr.info.info = &info as *const bpf_btf_info as u64;
-    attr.info.info_len = mem::size_of::<bpf_btf_info>() as u32;
-
-    match sys_bpf(bpf_cmd::BPF_OBJ_GET_INFO_BY_FD, &mut attr) {
-        Ok(_) => Ok(info),
-        Err((_, err)) => Err(err),
-    }
 }
 
 pub(crate) fn bpf_raw_tracepoint_open(name: Option<&CStr>, prog_fd: RawFd) -> SysResult<OwnedFd> {