//! The Linux `membarrier` syscall.
//!
//! # Safety
//!
//! This file defines an enum and a bitflags type that represent the same
//! set of values and are kept in sync.
#![allow(unsafe_code)]

use crate::process::Cpuid;
use crate::{backend, io};

pub use backend::process::types::MembarrierCommand;

#[cfg(linux_kernel)]
bitflags::bitflags! {
    /// A result from [`membarrier_query`].
    ///
    /// These flags correspond to values of [`MembarrierCommand`] which are
    /// supported in the OS.
    pub struct MembarrierQuery: u32 {
       /// `MEMBARRIER_CMD_GLOBAL` (also known as `MEMBARRIER_CMD_SHARED`)
       #[doc(alias = "SHARED")]
       #[doc(alias = "MEMBARRIER_CMD_SHARED")]
       const GLOBAL = MembarrierCommand::Global as _;
       /// `MEMBARRIER_CMD_GLOBAL_EXPEDITED`
       const GLOBAL_EXPEDITED = MembarrierCommand::GlobalExpedited as _;
       /// `MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED`
       const REGISTER_GLOBAL_EXPEDITED = MembarrierCommand::RegisterGlobalExpedited as _;
       /// `MEMBARRIER_CMD_PRIVATE_EXPEDITED`
       const PRIVATE_EXPEDITED = MembarrierCommand::PrivateExpedited as _;
       /// `MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED`
       const REGISTER_PRIVATE_EXPEDITED = MembarrierCommand::RegisterPrivateExpedited as _;
       /// `MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE`
       const PRIVATE_EXPEDITED_SYNC_CORE = MembarrierCommand::PrivateExpeditedSyncCore as _;
       /// `MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE`
       const REGISTER_PRIVATE_EXPEDITED_SYNC_CORE = MembarrierCommand::RegisterPrivateExpeditedSyncCore as _;
       /// `MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ` (since Linux 5.10)
       const PRIVATE_EXPEDITED_RSEQ = MembarrierCommand::PrivateExpeditedRseq as _;
       /// `MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ` (since Linux 5.10)
       const REGISTER_PRIVATE_EXPEDITED_RSEQ = MembarrierCommand::RegisterPrivateExpeditedRseq as _;
    }
}

#[cfg(linux_kernel)]
impl MembarrierQuery {
    /// Test whether this query result contains the given command.
    #[inline]
    pub fn contains_command(self, cmd: MembarrierCommand) -> bool {
        // SAFETY: `MembarrierCommand` is an enum that only contains values
        // also valid in `MembarrierQuery`.
        self.contains(unsafe { Self::from_bits_unchecked(cmd as _) })
    }
}

/// `membarrier(MEMBARRIER_CMD_QUERY, 0, 0)`—Query the supported `membarrier`
/// commands.
///
/// This function doesn't return a `Result` because it always succeeds; if
/// the underlying OS doesn't support the `membarrier` syscall, it returns
/// an empty `MembarrierQuery` value.
///
/// # References
///  - [Linux]
///
/// [Linux]: https://man7.org/linux/man-pages/man2/membarrier.2.html
#[inline]
#[doc(alias = "MEMBARRIER_CMD_QUERY")]
pub fn membarrier_query() -> MembarrierQuery {
    backend::process::syscalls::membarrier_query()
}

/// `membarrier(cmd, 0, 0)`—Perform a memory barrier.
///
/// # References
///  - [Linux]
///
/// [Linux]: https://man7.org/linux/man-pages/man2/membarrier.2.html
#[inline]
pub fn membarrier(cmd: MembarrierCommand) -> io::Result<()> {
    backend::process::syscalls::membarrier(cmd)
}

/// `membarrier(cmd, MEMBARRIER_CMD_FLAG_CPU, cpu)`—Perform a memory barrier
/// with a specific CPU.
///
/// # References
///  - [Linux]
///
/// [Linux]: https://man7.org/linux/man-pages/man2/membarrier.2.html
#[inline]
pub fn membarrier_cpu(cmd: MembarrierCommand, cpu: Cpuid) -> io::Result<()> {
    backend::process::syscalls::membarrier_cpu(cmd, cpu)
}