Re: [PATCH 14/36] aio: implement IOCB_CMD_POLL

Jeff Moyer
2018-03-05T21:52:00Z

Christoph Hellwig <hch@lst.de> writes:

> Simple one-shot poll through the io_submit() interface. To poll for
> a file descriptor the application should submit an iocb of type
> IOCB_CMD_POLL. It will poll the fd for the events specified in the
> the first 32 bits of the aio_buf field of the iocb.
>
> Unlike poll or epoll without EPOLLONESHOT this interface always works
> in one shot mode, that is once the iocb is completed, it will have to be
> resubmitted.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Also acked this one in the last posting.

Acked-by: Jeff Moyer <jmoyer@redhat.com>

> ---
> fs/aio.c | 102 +++++++++++++++++++++++++++++++++++++++++++
> include/uapi/linux/aio_abi.h | 6 +--
> 2 files changed, 104 insertions(+), 4 deletions(-)
>
> diff --git a/fs/aio.c b/fs/aio.c
> index da87cbf7c67a..0bafc4975d51 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -5,6 +5,7 @@
> * Implements an efficient asynchronous io interface.
> *
> * Copyright 2000, 2001, 2002 Red Hat, Inc. All Rights Reserved.
> + * Copyright 2018 Christoph Hellwig.
> *
> * See ../COPYING for licensing terms.
> */
> @@ -156,9 +157,17 @@ struct kioctx {
> unsigned id;
> };
>
> +struct poll_iocb {
> + struct file *file;
> + __poll_t events;
> + struct wait_queue_head *head;
> + struct wait_queue_entry wait;
> +};
> +
> struct aio_kiocb {
> union {
> struct kiocb rw;
> + struct poll_iocb poll;
> };
>
> struct kioctx *ki_ctx;
> @@ -1565,6 +1574,96 @@ static ssize_t aio_write(struct kiocb *req, struct iocb *iocb, bool vectored,
> return ret;
> }
>
> +static void __aio_complete_poll(struct poll_iocb *req, __poll_t mask)
> +{
> + fput(req->file);
> + aio_complete(container_of(req, struct aio_kiocb, poll),
> + mangle_poll(mask), 0);
> +}
> +
> +static void aio_complete_poll(struct poll_iocb *req, __poll_t mask)
> +{
> + struct aio_kiocb *iocb = container_of(req, struct aio_kiocb, poll);
> +
> + if (!(iocb->flags & AIO_IOCB_CANCELLED))
> + __aio_complete_poll(req, mask);
> +}
> +
> +static int aio_poll_cancel(struct kiocb *rw)
> +{
> + struct aio_kiocb *iocb = container_of(rw, struct aio_kiocb, rw);
> +
> + remove_wait_queue(iocb->poll.head, &iocb->poll.wait);
> + __aio_complete_poll(&iocb->poll, 0); /* no events to report */
> + return 0;
> +}
> +
> +static int aio_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
> + void *key)
> +{
> + struct poll_iocb *req = container_of(wait, struct poll_iocb, wait);
> + struct file *file = req->file;
> + __poll_t mask = key_to_poll(key);
> +
> + assert_spin_locked(&req->head->lock);
> +
> + /* for instances that support it check for an event match first: */
> + if (mask && !(mask & req->events))
> + return 0;
> +
> + mask = vfs_poll_mask(file, req->events);
> + if (!mask)
> + return 0;
> +
> + __remove_wait_queue(req->head, &req->wait);
> + aio_complete_poll(req, mask);
> + return 1;
> +}
> +
> +static ssize_t aio_poll(struct aio_kiocb *aiocb, struct iocb *iocb)
> +{
> + struct poll_iocb *req = &aiocb->poll;
> + unsigned long flags;
> + __poll_t mask;
> +
> + /* reject any unknown events outside the normal event mask. */
> + if ((u16)iocb->aio_buf != iocb->aio_buf)
> + return -EINVAL;
> + /* reject fields that are not defined for poll */
> + if (iocb->aio_offset || iocb->aio_nbytes || iocb->aio_rw_flags)
> + return -EINVAL;
> +
> + req->events = demangle_poll(iocb->aio_buf) | POLLERR | POLLHUP;
> + req->file = fget(iocb->aio_fildes);
> + if (unlikely(!req->file))
> + return -EBADF;
> +
> + req->head = vfs_get_poll_head(req->file, req->events);
> + if (!req->head) {
> + fput(req->file);
> + return -EINVAL; /* same as no support for IOCB_CMD_POLL */
> + }
> + if (IS_ERR(req->head)) {
> + mask = PTR_TO_POLL(req->head);
> + goto done;
> + }
> +
> + init_waitqueue_func_entry(&req->wait, aio_poll_wake);
> +
> + spin_lock_irqsave(&req->head->lock, flags);
> + mask = vfs_poll_mask(req->file, req->events);
> + if (!mask) {
> + __kiocb_set_cancel_fn(aiocb, aio_poll_cancel,
> + AIO_IOCB_DELAYED_CANCEL);
> + __add_wait_queue(req->head, &req->wait);
> + }
> + spin_unlock_irqrestore(&req->head->lock, flags);
> +done:
> + if (mask)
> + aio_complete_poll(req, mask);
> + return -EIOCBQUEUED;
> +}
> +
> static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
> struct iocb *iocb, bool compat)
> {
> @@ -1628,6 +1727,9 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
> case IOCB_CMD_PWRITEV:
> ret = aio_write(&req->rw, iocb, true, compat);
> break;
> + case IOCB_CMD_POLL:
> + ret = aio_poll(req, iocb);
> + break;
> default:
> pr_debug("invalid aio operation %d\n", iocb->aio_lio_opcode);
> ret = -EINVAL;
> diff --git a/include/uapi/linux/aio_abi.h b/include/uapi/linux/aio_abi.h
> index 2c0a3415beee..ed0185945bb2 100644
> --- a/include/uapi/linux/aio_abi.h
> +++ b/include/uapi/linux/aio_abi.h
> @@ -39,10 +39,8 @@ enum {
> IOCB_CMD_PWRITE = 1,
> IOCB_CMD_FSYNC = 2,
> IOCB_CMD_FDSYNC = 3,
> - /* These two are experimental.
> - * IOCB_CMD_PREADX = 4,
> - * IOCB_CMD_POLL = 5,
> - */
> + /* 4 was the experimental IOCB_CMD_PREADX */
> + IOCB_CMD_POLL = 5,
> IOCB_CMD_NOOP = 6,
> IOCB_CMD_PREADV = 7,
> IOCB_CMD_PWRITEV = 8,