change map_ids type

Make the optional field (map_ids) that's part of the
bpf_prog_get_info_by_fd syscall a raw slice reference rather than an
Option.  The user can pass a pre-initialized slice of length
info.nr_map_ids to ensure the map_ids buffer is populated, OR pass an
empty slice if they don't need the map_ids.

Signed-off-by: Andrew Stoycos <astoycos@redhat.com>

aya/src/programs/extension.rs

@@ -151,7 +151,7 @@ impl Extension {
 /// with the name `func_name` within that BTF object.
 fn get_btf_info(prog_fd: i32, func_name: &str) -> Result<(RawFd, u32), ProgramError> {
     // retrieve program information
-    let info = sys::bpf_prog_get_info_by_fd(prog_fd, None).map_err(|io_error| {
+    let info = sys::bpf_prog_get_info_by_fd(prog_fd, &[]).map_err(|io_error| {
         ProgramError::SyscallError {
             call: "bpf_prog_get_info_by_fd",
             io_error,

aya/src/programs/lirc_mode2.rs

@@ -132,7 +132,7 @@ impl LircLink {
 
     /// Get ProgramInfo from this link
     pub fn info(&self) -> Result<ProgramInfo, ProgramError> {
-        match bpf_prog_get_info_by_fd(self.prog_fd, None) {
+        match bpf_prog_get_info_by_fd(self.prog_fd, &[]) {
             Ok(info) => Ok(ProgramInfo(info)),
             Err(io_error) => Err(ProgramError::SyscallError {
                 call: "bpf_prog_get_info_by_fd",

aya/src/programs/mod.rs

@@ -497,7 +497,7 @@ impl<T: Link> ProgramData<T> {
             })? as RawFd;
 
         let info =
-            bpf_prog_get_info_by_fd(fd, None).map_err(|io_error| ProgramError::SyscallError {
+            bpf_prog_get_info_by_fd(fd, &[]).map_err(|io_error| ProgramError::SyscallError {
                 call: "bpf_prog_get_info_by_fd",
                 io_error,
             })?;
@@ -932,7 +932,7 @@ macro_rules! impl_program_info {
                 pub fn program_info(&self) -> Result<ProgramInfo, ProgramError> {
                     let fd = self.fd().ok_or(ProgramError::NotLoaded)?;
 
-                    bpf_prog_get_info_by_fd(fd.as_raw_fd(), None)
+                    bpf_prog_get_info_by_fd(fd.as_raw_fd(), &[])
                         .map_err(|io_error| ProgramError::SyscallError {
                             call: "bpf_prog_get_info_by_fd",
                             io_error,
@@ -1022,15 +1022,11 @@ impl ProgramInfo {
     /// Returns the ids of the maps maps used by the program.
     pub fn map_ids(&self) -> Result<Vec<u32>, ProgramError> {
         let fd = self.fd()?;
+        let map_ids = vec![0u32; self.0.nr_map_ids as usize];
 
-        let len = self.0.nr_map_ids;
-        let mut map_ids = vec![0u32; len as usize];
-
-        bpf_prog_get_info_by_fd(fd, Some(&mut map_ids)).map_err(|io_error| {
-            ProgramError::SyscallError {
-                call: "bpf_prog_get_info_by_fd",
-                io_error,
-            }
+        bpf_prog_get_info_by_fd(fd, &map_ids).map_err(|io_error| ProgramError::SyscallError {
+            call: "bpf_prog_get_info_by_fd",
+            io_error,
         })?;
 
         unsafe { libc::close(fd) };
@@ -1099,7 +1095,7 @@ impl ProgramInfo {
             })? as RawFd;
 
         let info =
-            bpf_prog_get_info_by_fd(fd, None).map_err(|io_error| ProgramError::SyscallError {
+            bpf_prog_get_info_by_fd(fd, &[]).map_err(|io_error| ProgramError::SyscallError {
                 call: "bpf_prog_get_info_by_fd",
                 io_error,
             })?;
@@ -1135,7 +1131,7 @@ impl Iterator for ProgramsIter {
                             io_error,
                         })
                         .and_then(|fd| {
-                            let info = bpf_prog_get_info_by_fd(fd, None)
+                            let info = bpf_prog_get_info_by_fd(fd, &[])
                                 .map_err(|io_error| ProgramError::SyscallError {
                                     call: "bpf_prog_get_info_by_fd",
                                     io_error,

aya/src/sys/bpf.rs

@@ -473,15 +473,12 @@ pub(crate) fn bpf_prog_get_fd_by_id(prog_id: u32) -> Result<RawFd, io::Error> {
 
 pub(crate) fn bpf_prog_get_info_by_fd(
     prog_fd: RawFd,
-    map_ids: Option<&mut [u32]>,
+    map_ids: &[u32],
 ) -> Result<bpf_prog_info, io::Error> {
     let mut attr = unsafe { mem::zeroed::<bpf_attr>() };
     let mut info = unsafe { mem::zeroed::<bpf_prog_info>() };
-
-    if let Some(i) = map_ids {
-        info.map_ids = i.as_mut_ptr() as u64;
-        info.nr_map_ids = i.len() as u32;
-    };
+    info.map_ids = map_ids.as_ptr() as u64;
+    info.nr_map_ids = map_ids.len() as u32;
 
     attr.info.bpf_fd = prog_fd as u32;
     attr.info.info = &info as *const _ as u64;