asterinas/kernel/src/syscall/futex.rs

// SPDX-License-Identifier: MPL-2.0

use core::time::Duration;

use crate::{
    get_current_userspace,
    prelude::*,
    process::posix_thread::futex::{
        futex_op_and_flags_from_u32, futex_requeue, futex_wait, futex_wait_bitset, futex_wake,
        futex_wake_bitset, FutexFlags, FutexOp,
    },
    syscall::SyscallReturn,
    time::{
        clocks::{MonotonicClock, RealTimeClock},
        timer::Timeout,
        timespec_t,
        wait::ManagedTimeout,
    },
};

pub fn sys_futex(
    futex_addr: Vaddr,
    futex_op: i32,
    futex_val: u64,
    utime_addr: Vaddr,
    futex_new_addr: u64,
    bitset: u64,
    ctx: &Context,
) -> Result<SyscallReturn> {
    let (futex_op, futex_flags) = futex_op_and_flags_from_u32(futex_op as _)?;
    debug!(
        "futex_op = {:?}, futex_flags = {:?}, futex_addr = 0x{:x}, futex_val = 0x{:x}",
        futex_op, futex_flags, futex_addr, futex_val
    );

    let get_futex_val = |val: i32| -> Result<usize> {
        if val < 0 {
            return_errno_with_message!(Errno::EINVAL, "the futex val must not be negative");
        }
        Ok(val as usize)
    };

    let get_futex_timeout = |timeout_addr: Vaddr| -> Result<Option<ManagedTimeout<'static>>> {
        if timeout_addr == 0 {
            return Ok(None);
        }

        let timeout = {
            let time_spec: timespec_t = get_current_userspace!().read_val(timeout_addr)?;
            Duration::try_from(time_spec)?
        };

        let is_real_time = futex_flags.contains(FutexFlags::FUTEX_CLOCK_REALTIME);
        if is_real_time && futex_op == FutexOp::FUTEX_WAIT {
            // Ref: <https://github.com/torvalds/linux/commit/4fbf5d6837bf81fd7a27d771358f4ee6c4f243f8>
            return_errno_with_message!(Errno::ENOSYS, "FUTEX_WAIT cannot use CLOCK_REALTIME");
        }

        let timeout = {
            // From man(2) futex:
            // for FUTEX_WAIT, timeout is interpreted as a relative value.
            // This differs from other futex operations,
            // where timeout is interpreted as an absolute value.
            // To obtain the equivalent of FUTEX_WAIT with an absolute timeout,
            // employ FUTEX_WAIT_BITSET with val3 specified as FUTEX_BITSET_MATCH_ANY.
            if futex_op == FutexOp::FUTEX_WAIT {
                Timeout::After(timeout)
            } else {
                Timeout::When(timeout)
            }
        };

        let timer_manager = if is_real_time {
            debug!("futex timeout = {:?}, clock = CLOCK_REALTIME", timeout);
            RealTimeClock::timer_manager()
        } else {
            debug!("futex timeout = {:?}, clock = CLOCK_MONOTONIC", timeout);
            MonotonicClock::timer_manager()
        };

        Ok(Some(ManagedTimeout::new_with_manager(
            timeout,
            timer_manager,
        )))
    };

    let pid = if futex_flags.contains(FutexFlags::FUTEX_PRIVATE) {
        Some(ctx.process.pid())
    } else {
        None
    };
    let res = match futex_op {
        FutexOp::FUTEX_WAIT => {
            let timeout = get_futex_timeout(utime_addr)?;
            futex_wait(futex_addr as _, futex_val as _, timeout, ctx, pid).map(|_| 0)
        }
        FutexOp::FUTEX_WAIT_BITSET => {
            let timeout = get_futex_timeout(utime_addr)?;
            futex_wait_bitset(
                futex_addr as _,
                futex_val as _,
                timeout,
                bitset as _,
                ctx,
                pid,
            )
            .map(|_| 0)
        }
        FutexOp::FUTEX_WAKE => {
            // From gVisor/test/syscalls/linux/futex.cc:260: "The Linux kernel wakes one waiter even if val is 0 or negative."
            // To be consistent with Linux, we set the max_count to 1 if it is 0 or negative.
            let max_count = (futex_val as i32).max(1) as usize;
            futex_wake(futex_addr as _, max_count, pid).map(|count| count as isize)
        }
        FutexOp::FUTEX_WAKE_BITSET => {
            // From gVisor/test/syscalls/linux/futex.cc:260: "The Linux kernel wakes one waiter even if val is 0 or negative."
            // To be consistent with Linux, we set the max_count to 1 if it is 0 or negative.
            let max_count = (futex_val as i32).max(1) as usize;
            futex_wake_bitset(futex_addr as _, max_count, bitset as _, pid)
                .map(|count| count as isize)
        }
        FutexOp::FUTEX_REQUEUE => {
            let max_nwakes = get_futex_val(futex_val as i32)?;
            let max_nrequeues = get_futex_val(utime_addr as i32)?;
            futex_requeue(
                futex_addr as _,
                max_nwakes,
                max_nrequeues,
                futex_new_addr as _,
                pid,
            )
            .map(|nwakes| nwakes as _)
        }
        _ => {
            warn!("futex op = {:?}", futex_op);
            return_errno_with_message!(Errno::EINVAL, "unsupported futex op");
        }
    }
    .map_err(|e| {
        // From Linux manual, Futex returns `ETIMEDOUT` instead of `ETIME`
        if e.error() == Errno::ETIME {
            Error::with_message(Errno::ETIMEDOUT, "futex wait timeout")
        } else {
            e
        }
    })?;

    debug!("futex returns, tid= {} ", ctx.posix_thread.tid());
    Ok(SyscallReturn::Return(res as _))
}