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    Subject[RFC 4/4] io_uring: implement futex wait
    Date
    Add futex wait requests, those always go through io-wq for simplicity.

    Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
    ---
    fs/io_uring.c | 38 ++++++++++++++++++++++++++++-------
    include/uapi/linux/io_uring.h | 2 +-
    2 files changed, 32 insertions(+), 8 deletions(-)

    diff --git a/fs/io_uring.c b/fs/io_uring.c
    index 99f4f8d9f685..9c3d075a6647 100644
    --- a/fs/io_uring.c
    +++ b/fs/io_uring.c
    @@ -670,8 +670,15 @@ struct io_futex {
    struct file *file;
    unsigned int futex_op;

    - unsigned int nr_wake;
    - unsigned int wake_op_arg;
    + union {
    + /* wake */
    + struct {
    + unsigned int nr_wake;
    + unsigned int wake_op_arg;
    + };
    + /* wait */
    + u32 val;
    + };
    unsigned int flags;
    void __user *uaddr;
    };
    @@ -5894,10 +5901,23 @@ static int io_futex_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
    return -EINVAL;

    v = READ_ONCE(sqe->off);
    - f->nr_wake = (u32)v;
    - f->wake_op_arg = (u32)(v >> 32);
    - f->futex_op = READ_ONCE(sqe->futex_op);
    f->uaddr = u64_to_user_ptr(READ_ONCE(sqe->addr));
    + f->futex_op = READ_ONCE(sqe->futex_op);
    +
    + switch (f->futex_op) {
    + case IORING_FUTEX_WAKE_OP:
    + f->nr_wake = (u32)v;
    + f->wake_op_arg = (u32)(v >> 32);
    + break;
    + case IORING_FUTEX_WAIT:
    + f->val = (u32)v;
    + if (unlikely(v >> 32))
    + return -EINVAL;
    + break;
    + default:
    + return -EINVAL;
    + }
    +
    return 0;
    }

    @@ -5916,8 +5936,12 @@ static int io_futex(struct io_kiocb *req, unsigned int issue_flags)
    if (nonblock && ret == -EAGAIN)
    return -EAGAIN;
    break;
    - default:
    - ret = -EINVAL;
    + case IORING_FUTEX_WAIT:
    + if (nonblock)
    + return -EAGAIN;
    + ret = futex_wait(f->uaddr, f->flags, f->val, NULL,
    + FUTEX_BITSET_MATCH_ANY);
    + break;
    }

    if (ret < 0)
    diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
    index 6fa5a6e59934..7ab11ee2ce12 100644
    --- a/include/uapi/linux/io_uring.h
    +++ b/include/uapi/linux/io_uring.h
    @@ -186,7 +186,7 @@ enum {

    enum {
    IORING_FUTEX_WAKE_OP = 0,
    -
    + IORING_FUTEX_WAIT,
    IORING_FUTEX_LAST,
    };

    --
    2.31.1
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