aya: Implement Maps/Arrays of Maps

Signed-off-by: Dave Tucker <dave@dtucker.co.uk>

aya/src/maps/mod.rs

@@ -50,6 +50,7 @@ mod map_lock;
 
 pub mod array;
 pub mod hash_map;
+pub mod of_maps;
 pub mod perf;
 pub mod queue;
 pub mod sock;
@@ -59,6 +60,7 @@ pub mod stack_trace;
 pub use array::{Array, PerCpuArray, ProgramArray};
 pub use hash_map::{HashMap, PerCpuHashMap};
 pub use map_lock::*;
+pub use of_maps::{Array as ArrayOfMaps, HashMap as HashMapOfMaps};
 pub use perf::PerfEventArray;
 pub use queue::Queue;
 pub use sock::{SockHash, SockMap};

aya/src/maps/of_maps/array.rs

@@ -0,0 +1,147 @@
+//! An array of eBPF maps.
+
+use std::{
+    convert::TryFrom,
+    mem,
+    ops::{Deref, DerefMut},
+    os::unix::{io::IntoRawFd, prelude::RawFd},
+};
+
+use crate::{
+    generated::bpf_map_type::BPF_MAP_TYPE_ARRAY_OF_MAPS,
+    maps::{of_maps::MapOfMaps, Map, MapError, MapKeys, MapRef, MapRefMut},
+    sys::{bpf_map_delete_elem, bpf_map_get_fd_by_id, bpf_map_lookup_elem, bpf_map_update_elem},
+};
+
+/// An array of eBPF Maps
+///
+/// A `Array` is used to store references to other maps.
+///
+/// # Minimum kernel version
+///
+/// The minimum kernel version required to use this feature is 4.14.
+#[doc(alias = "BPF_MAP_TYPE_ARRAY_OF_MAPS")]
+pub struct Array<T: Deref<Target = Map>> {
+    pub(crate) inner: T,
+}
+
+impl<T: Deref<Target = Map>> Array<T> {
+    fn new(map: T) -> Result<Array<T>, MapError> {
+        let map_type = map.obj.def.map_type;
+        if map_type != BPF_MAP_TYPE_ARRAY_OF_MAPS as u32 {
+            return Err(MapError::InvalidMapType {
+                map_type: map_type as u32,
+            });
+        }
+        let expected = mem::size_of::<u32>();
+        let size = map.obj.def.key_size as usize;
+        if size != expected {
+            return Err(MapError::InvalidKeySize { size, expected });
+        }
+
+        let expected = mem::size_of::<u32>();
+        let size = map.obj.def.value_size as usize;
+        if size != expected {
+            return Err(MapError::InvalidValueSize { size, expected });
+        }
+        let _fd = map.fd_or_err()?;
+
+        Ok(Array { inner: map })
+    }
+
+    /// An iterator over the indices of the array that point to a map. The iterator item type
+    /// is `Result<u32, MapError>`.
+    pub unsafe fn indices(&self) -> MapKeys<'_, u32> {
+        MapKeys::new(&self.inner)
+    }
+
+    fn check_bounds(&self, index: u32) -> Result<(), MapError> {
+        let max_entries = self.inner.obj.def.max_entries;
+        if index >= self.inner.obj.def.max_entries {
+            Err(MapError::OutOfBounds { index, max_entries })
+        } else {
+            Ok(())
+        }
+    }
+
+    /// Returns the fd of the map stored at the given index.
+    ///
+    /// # Errors
+    ///
+    /// Returns [`MapError::OutOfBounds`] if `index` is out of bounds, [`MapError::SyscallError`]
+    /// if `bpf_map_lookup_elem` fails.
+    pub fn get(&self, index: &u32, flags: u64) -> Result<RawFd, MapError> {
+        self.check_bounds(*index)?;
+        let fd = self.inner.fd_or_err()?;
+
+        let id = bpf_map_lookup_elem(fd, index, flags)
+            .map_err(|(code, io_error)| MapError::SyscallError {
+                call: "bpf_map_lookup_elem".to_owned(),
+                code,
+                io_error,
+            })?
+            .ok_or(MapError::KeyNotFound)?;
+        let inner_fd = bpf_map_get_fd_by_id(id).map_err(|io_error| MapError::SyscallError {
+            call: "bpf_map_get_fd_by_id".to_owned(),
+            code: 0,
+            io_error,
+        })?;
+        Ok(inner_fd as RawFd)
+    }
+}
+
+impl<T: Deref<Target = Map> + DerefMut<Target = Map>> Array<T> {
+    /// Stores a map fd into the map.
+    pub fn set<I: IntoRawFd>(&mut self, index: u32, map: I, flags: u64) -> Result<(), MapError> {
+        let fd = self.inner.fd_or_err()?;
+        let map_fd = map.into_raw_fd();
+        self.check_bounds(index)?;
+        bpf_map_update_elem(fd, &index, &map_fd, flags).map_err(|(code, io_error)| {
+            MapError::SyscallError {
+                call: "bpf_map_update_elem".to_owned(),
+                code,
+                io_error,
+            }
+        })?;
+        // safety: we're closing a RawFd which we have ownership of
+        // this is required because inserting this in to the map causes
+        // there to be a reference to the map in both kernel and userspace
+        unsafe { libc::close(map_fd) };
+        Ok(())
+    }
+
+    /// Removes the map stored at `index` from the map.
+    pub fn delete(&mut self, index: &u32) -> Result<(), MapError> {
+        let fd = self.inner.fd_or_err()?;
+        self.check_bounds(*index)?;
+        bpf_map_delete_elem(fd, index)
+            .map(|_| ())
+            .map_err(|(code, io_error)| MapError::SyscallError {
+                call: "bpf_map_delete_elem".to_owned(),
+                code,
+                io_error,
+            })
+    }
+}
+
+impl<T: Deref<Target = Map> + DerefMut<Target = Map>> MapOfMaps for Array<T> {
+    fn fd_or_err(&self) -> Result<RawFd, MapError> {
+        self.inner.fd_or_err()
+    }
+}
+
+impl TryFrom<MapRef> for Array<MapRef> {
+    type Error = MapError;
+
+    fn try_from(a: MapRef) -> Result<Array<MapRef>, MapError> {
+        Array::new(a)
+    }
+}
+
+impl TryFrom<MapRefMut> for Array<MapRefMut> {
+    type Error = MapError;
+
+    fn try_from(a: MapRefMut) -> Result<Array<MapRefMut>, MapError> {
+        Array::new(a)
+    }
+}

aya/src/maps/of_maps/hash_map.rs

@@ -0,0 +1,129 @@
+use std::{
+    convert::TryFrom,
+    marker::PhantomData,
+    ops::{Deref, DerefMut},
+    os::unix::io::{IntoRawFd, RawFd},
+};
+
+use crate::{
+    generated::bpf_map_type::BPF_MAP_TYPE_HASH_OF_MAPS,
+    maps::{
+        hash_map, of_maps::MapOfMaps, IterableMap, Map, MapError, MapIter, MapKeys, MapRef,
+        MapRefMut,
+    },
+    sys::{bpf_map_get_fd_by_id, bpf_map_lookup_elem},
+    Pod,
+};
+
+/// A hash map of eBPF Maps.
+///
+/// A `HashMap` is used to store references to eBPF Maps
+///
+/// # Minimum kernel version
+///
+/// The minimum kernel version required to use this feature is 4.18.
+#[doc(alias = "BPF_MAP_TYPE_HASH_OF_MAPS")]
+pub struct HashMap<T: Deref<Target = Map>, K> {
+    inner: T,
+    _k: PhantomData<K>,
+}
+
+impl<T: Deref<Target = Map>, K: Pod> HashMap<T, K> {
+    pub(crate) fn new(map: T) -> Result<HashMap<T, K>, MapError> {
+        let map_type = map.obj.def.map_type;
+
+        // validate the map definition
+        if map_type != BPF_MAP_TYPE_HASH_OF_MAPS as u32 {
+            return Err(MapError::InvalidMapType {
+                map_type: map_type as u32,
+            });
+        }
+        hash_map::check_kv_size::<K, u32>(&map)?;
+        let _ = map.fd_or_err()?;
+
+        Ok(HashMap {
+            inner: map,
+            _k: PhantomData,
+        })
+    }
+
+    /// Returns the fd of the map stored at the given key.
+    pub unsafe fn get(&self, key: &K, flags: u64) -> Result<RawFd, MapError> {
+        let fd = self.inner.deref().fd_or_err()?;
+        let id = bpf_map_lookup_elem(fd, key, flags)
+            .map_err(|(code, io_error)| MapError::SyscallError {
+                call: "bpf_map_lookup_elem".to_owned(),
+                code,
+                io_error,
+            })?
+            .ok_or(MapError::KeyNotFound)?;
+        let inner_fd = bpf_map_get_fd_by_id(id).map_err(|io_error| MapError::SyscallError {
+            call: "bpf_map_get_fd_by_id".to_owned(),
+            code: 0,
+            io_error,
+        })?;
+        Ok(inner_fd as RawFd)
+    }
+
+    /// An iterator visiting all key-value pairs in arbitrary order. The
+    /// iterator item type is `Result<(K, V), MapError>`.
+    pub unsafe fn iter(&self) -> MapIter<'_, K, RawFd> {
+        MapIter::new(self)
+    }
+
+    /// An iterator visiting all keys in arbitrary order. The iterator element
+    /// type is `Result<K, MapError>`.
+    pub unsafe fn keys(&self) -> MapKeys<'_, K> {
+        MapKeys::new(&self.inner)
+    }
+}
+
+impl<T: DerefMut<Target = Map>, K: Pod> HashMap<T, K> {
+    /// Inserts a map under the given key.
+    pub fn insert<I: IntoRawFd>(&mut self, key: K, value: I, flags: u64) -> Result<(), MapError> {
+        let map_fd = value.into_raw_fd();
+        hash_map::insert(&mut self.inner, key, map_fd, flags)?;
+        // safety: we're closing a RawFd which we have ownership of
+        // this is required because inserting this in to the map causes
+        // there to be a reference to the map in both kernel and userspace
+        unsafe { libc::close(map_fd) };
+        Ok(())
+    }
+
+    /// Removes a map from the map.
+    pub fn remove(&mut self, key: &K) -> Result<(), MapError> {
+        hash_map::remove(&mut self.inner, key)
+    }
+}
+
+impl<T: Deref<Target = Map>, K: Pod> IterableMap<K, RawFd> for HashMap<T, K> {
+    fn map(&self) -> &Map {
+        &self.inner
+    }
+
+    unsafe fn get(&self, key: &K) -> Result<RawFd, MapError> {
+        HashMap::get(self, key, 0)
+    }
+}
+
+impl<T: DerefMut<Target = Map>, K: Pod> MapOfMaps for HashMap<T, K> {
+    fn fd_or_err(&self) -> Result<RawFd, MapError> {
+        self.inner.fd_or_err()
+    }
+}
+
+impl<K: Pod> TryFrom<MapRef> for HashMap<MapRef, K> {
+    type Error = MapError;
+
+    fn try_from(a: MapRef) -> Result<HashMap<MapRef, K>, MapError> {
+        HashMap::new(a)
+    }
+}
+
+impl<K: Pod> TryFrom<MapRefMut> for HashMap<MapRefMut, K> {
+    type Error = MapError;
+
+    fn try_from(a: MapRefMut) -> Result<HashMap<MapRefMut, K>, MapError> {
+        HashMap::new(a)
+    }
+}

aya/src/maps/of_maps/mod.rs

@@ -0,0 +1,14 @@
+//! Maps of maps
+mod array;
+mod hash_map;
+
+use std::os::unix::io::RawFd;
+
+use crate::maps::MapError;
+
+pub use array::Array;
+pub use hash_map::HashMap;
+
+pub trait MapOfMaps {
+    fn fd_or_err(&self) -> Result<RawFd, MapError>;
+}

aya/src/sys/bpf.rs

@@ -234,6 +234,17 @@ pub(crate) fn bpf_map_get_next_key<K>(
     }
 }
 
+pub(crate) fn bpf_map_get_fd_by_id(map_id: u32) -> Result<RawFd, io::Error> {
+    let mut attr = unsafe { mem::zeroed::<bpf_attr>() };
+
+    attr.__bindgen_anon_6.__bindgen_anon_1.map_id = map_id;
+
+    match sys_bpf(bpf_cmd::BPF_MAP_GET_FD_BY_ID, &attr) {
+        Ok(v) => Ok(v as RawFd),
+        Err((_, err)) => Err(err),
+    }
+}
+
 // since kernel 5.7
 pub(crate) fn bpf_link_create(
     prog_fd: RawFd,