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//! An array of eBPF program file descriptors used as a jump table.

use std::{
    convert::TryFrom,
    mem,
    ops::{Deref, DerefMut},
    os::unix::prelude::RawFd,
};

use crate::{
    generated::bpf_map_type::BPF_MAP_TYPE_PROG_ARRAY,
    maps::{Map, MapError, MapKeys, MapRef, MapRefMut},
    programs::ProgramFd,
    sys::{bpf_map_delete_elem, bpf_map_update_elem},
};

/// An array of eBPF program file descriptors used as a jump table.
///
/// eBPF programs can jump to other programs calling `bpf_tail_call(ctx,
/// prog_array, index)`. You can use [`ProgramArray`] to configure which
/// programs correspond to which jump indexes.
///
/// # Examples
/// ```no_run
/// # let bpf = aya::Bpf::load(&[], None)?;
/// use aya::maps::ProgramArray;
/// use aya::programs::CgroupSkb;
/// use std::convert::{TryFrom, TryInto};
///
/// let mut prog_array = ProgramArray::try_from(bpf.map_mut("JUMP_TABLE")?)?;
/// let prog_0: &CgroupSkb = bpf.program("example_prog_0")?.try_into()?;
/// let prog_1: &CgroupSkb = bpf.program("example_prog_1")?.try_into()?;
/// let prog_2: &CgroupSkb = bpf.program("example_prog_2")?.try_into()?;
///
/// let flags = 0;
///
/// // bpf_tail_call(ctx, JUMP_TABLE, 0) will jump to prog_0
/// prog_array.set(0, prog_0, flags);
///
/// // bpf_tail_call(ctx, JUMP_TABLE, 1) will jump to prog_1
/// prog_array.set(1, prog_1, flags);
///
/// // bpf_tail_call(ctx, JUMP_TABLE, 2) will jump to prog_2
/// prog_array.set(2, prog_2, flags);
/// # Ok::<(), aya::BpfError>(())
/// ```
#[doc(alias = "BPF_MAP_TYPE_PROG_ARRAY")]
pub struct ProgramArray<T: Deref<Target = Map>> {
    inner: T,
}

impl<T: Deref<Target = Map>> ProgramArray<T> {
    fn new(map: T) -> Result<ProgramArray<T>, MapError> {
        let map_type = map.obj.def.map_type;
        if map_type != BPF_MAP_TYPE_PROG_ARRAY 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::<RawFd>();
        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(ProgramArray { inner: map })
    }

    /// An iterator over the indices of the array that point to a program. 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(())
        }
    }
}

impl<T: Deref<Target = Map> + DerefMut<Target = Map>> ProgramArray<T> {
    /// Sets the target program file descriptor for the given index in the jump table.
    ///
    /// When an eBPF program calls `bpf_tail_call(ctx, prog_array, index)`, control
    /// flow will jump to `program`.
    pub fn set(&mut self, index: u32, program: &dyn ProgramFd, flags: u64) -> Result<(), MapError> {
        let fd = self.inner.fd_or_err()?;
        self.check_bounds(index)?;
        let prog_fd = program.fd().ok_or(MapError::ProgramNotLoaded)?;

        bpf_map_update_elem(fd, &index, &prog_fd, flags).map_err(|(code, io_error)| {
            MapError::SyscallError {
                call: "bpf_map_update_elem".to_owned(),
                code,
                io_error,
            }
        })?;
        Ok(())
    }

    /// Clears the value at index in the jump table.
    ///
    /// Calling `bpf_tail_call(ctx, prog_array, index)` on an index that has been cleared returns an
    /// error.
    pub fn clear_index(&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 TryFrom<MapRef> for ProgramArray<MapRef> {
    type Error = MapError;

    fn try_from(a: MapRef) -> Result<ProgramArray<MapRef>, MapError> {
        ProgramArray::new(a)
    }
}

impl TryFrom<MapRefMut> for ProgramArray<MapRefMut> {
    type Error = MapError;

    fn try_from(a: MapRefMut) -> Result<ProgramArray<MapRefMut>, MapError> {
        ProgramArray::new(a)
    }
}