Subject: Re: [PATCH 12/36] fs: add new vfs_poll and file_can_poll helpers

From: "Darrick J. Wong" <[email-masked]>
Date: Mon, 19 Mar 2018 19:27:34 -0700

On Mon, Mar 05, 2018 at 01:27:19PM -0800, Christoph Hellwig wrote:
> These abstract out calls to the poll method in preparation for changes
> in how we poll.
> 
> Signed-off-by: Christoph Hellwig <[email-masked]>
> ---
>  drivers/staging/comedi/drivers/serial2002.c |  4 ++--
>  drivers/vfio/virqfd.c                       |  2 +-
>  drivers/vhost/vhost.c                       |  2 +-
>  fs/eventpoll.c                              |  5 ++---
>  fs/select.c                                 | 23 ++++++++---------------
>  include/linux/poll.h                        | 12 ++++++++++++
>  mm/memcontrol.c                             |  2 +-

For the fs/include/mm changes,
Reviewed-by: Darrick J. Wong <[email-masked]>

The other conversions look fine to me too but I've never looked at them
before. :)

--D

>  net/9p/trans_fd.c                           | 18 ++++--------------
>  virt/kvm/eventfd.c                          |  2 +-
>  9 files changed, 32 insertions(+), 38 deletions(-)
> 
> diff --git a/drivers/staging/comedi/drivers/serial2002.c b/drivers/staging/comedi/drivers/serial2002.c
> index b3f3b4a201af..5471b2212a62 100644
> --- a/drivers/staging/comedi/drivers/serial2002.c
> +++ b/drivers/staging/comedi/drivers/serial2002.c
> @@ -113,7 +113,7 @@ static void serial2002_tty_read_poll_wait(struct file *f, int timeout)
>  		long elapsed;
>  		__poll_t mask;
>  
> -		mask = f->f_op->poll(f, &table.pt);
> +		mask = vfs_poll(f, &table.pt);
>  		if (mask & (EPOLLRDNORM | EPOLLRDBAND | EPOLLIN |
>  			    EPOLLHUP | EPOLLERR)) {
>  			break;
> @@ -136,7 +136,7 @@ static int serial2002_tty_read(struct file *f, int timeout)
>  
>  	result = -1;
>  	if (!IS_ERR(f)) {
> -		if (f->f_op->poll) {
> +		if (file_can_poll(f)) {
>  			serial2002_tty_read_poll_wait(f, timeout);
>  
>  			if (kernel_read(f, &ch, 1, &pos) == 1)
> diff --git a/drivers/vfio/virqfd.c b/drivers/vfio/virqfd.c
> index 085700f1be10..2a1be859ee71 100644
> --- a/drivers/vfio/virqfd.c
> +++ b/drivers/vfio/virqfd.c
> @@ -166,7 +166,7 @@ int vfio_virqfd_enable(void *opaque,
>  	init_waitqueue_func_entry(&virqfd->wait, virqfd_wakeup);
>  	init_poll_funcptr(&virqfd->pt, virqfd_ptable_queue_proc);
>  
> -	events = irqfd.file->f_op->poll(irqfd.file, &virqfd->pt);
> +	events = vfs_poll(irqfd.file, &virqfd->pt);
>  
>  	/*
>  	 * Check if there was an event already pending on the eventfd
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 1b3e8d2d5c8b..4d27e288bb1d 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -208,7 +208,7 @@ int vhost_poll_start(struct vhost_poll *poll, struct file *file)
>  	if (poll->wqh)
>  		return 0;
>  
> -	mask = file->f_op->poll(file, &poll->table);
> +	mask = vfs_poll(file, &poll->table);
>  	if (mask)
>  		vhost_poll_wakeup(&poll->wait, 0, 0, poll_to_key(mask));
>  	if (mask & EPOLLERR) {
> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> index 0f3494ed3ed0..2bebae5a38cf 100644
> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
> @@ -884,8 +884,7 @@ static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt,
>  
>  	pt->_key = epi->event.events;
>  	if (!is_file_epoll(epi->ffd.file))
> -		return epi->ffd.file->f_op->poll(epi->ffd.file, pt) &
> -		       epi->event.events;
> +		return vfs_poll(epi->ffd.file, pt) & epi->event.events;
>  
>  	ep = epi->ffd.file->private_data;
>  	poll_wait(epi->ffd.file, &ep->poll_wait, pt);
> @@ -2020,7 +2019,7 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
>  
>  	/* The target file descriptor must support poll */
>  	error = -EPERM;
> -	if (!tf.file->f_op->poll)
> +	if (!file_can_poll(tf.file))
>  		goto error_tgt_fput;
>  
>  	/* Check if EPOLLWAKEUP is allowed */
> diff --git a/fs/select.c b/fs/select.c
> index c6c504a814f9..ba91103707ea 100644
> --- a/fs/select.c
> +++ b/fs/select.c
> @@ -502,14 +502,10 @@ static int do_select(int n, fd_set_bits *fds, struct timespec64 *end_time)
>  					continue;
>  				f = fdget(i);
>  				if (f.file) {
> -					const struct file_operations *f_op;
> -					f_op = f.file->f_op;
> -					mask = DEFAULT_POLLMASK;
> -					if (f_op->poll) {
> -						wait_key_set(wait, in, out,
> -							     bit, busy_flag);
> -						mask = (*f_op->poll)(f.file, wait);
> -					}
> +					wait_key_set(wait, in, out, bit,
> +						     busy_flag);
> +					mask = vfs_poll(f.file, wait);
> +
>  					fdput(f);
>  					if ((mask & POLLIN_SET) && (in & bit)) {
>  						res_in |= bit;
> @@ -819,13 +815,10 @@ static inline __poll_t do_pollfd(struct pollfd *pollfd, poll_table *pwait,
>  
>  	/* userland u16 ->events contains POLL... bitmap */
>  	filter = demangle_poll(pollfd->events) | EPOLLERR | EPOLLHUP;
> -	mask = DEFAULT_POLLMASK;
> -	if (f.file->f_op->poll) {
> -		pwait->_key = filter | busy_flag;
> -		mask = f.file->f_op->poll(f.file, pwait);
> -		if (mask & busy_flag)
> -			*can_busy_poll = true;
> -	}
> +	pwait->_key = filter | busy_flag;
> +	mask = vfs_poll(f.file, pwait);
> +	if (mask & busy_flag)
> +		*can_busy_poll = true;
>  	mask &= filter;		/* Mask out unneeded events. */
>  	fdput(f);
>  
> diff --git a/include/linux/poll.h b/include/linux/poll.h
> index a3576da63377..7e0fdcf905d2 100644
> --- a/include/linux/poll.h
> +++ b/include/linux/poll.h
> @@ -74,6 +74,18 @@ static inline void init_poll_funcptr(poll_table *pt, poll_queue_proc qproc)
>  	pt->_key   = ~(__poll_t)0; /* all events enabled */
>  }
>  
> +static inline bool file_can_poll(struct file *file)
> +{
> +	return file->f_op->poll;
> +}
> +
> +static inline __poll_t vfs_poll(struct file *file, struct poll_table_struct *pt)
> +{
> +	if (unlikely(!file->f_op->poll))
> +		return DEFAULT_POLLMASK;
> +	return file->f_op->poll(file, pt);
> +}
> +
>  struct poll_table_entry {
>  	struct file *filp;
>  	__poll_t key;
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 670e99b68aa6..8774ece5c3c3 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3849,7 +3849,7 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
>  	if (ret)
>  		goto out_put_css;
>  
> -	efile.file->f_op->poll(efile.file, &event->pt);
> +	vfs_poll(efile.file, &event->pt);
>  
>  	spin_lock(&memcg->event_list_lock);
>  	list_add(&event->list, &memcg->event_list);
> diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
> index 0cfba919d167..3811775692d0 100644
> --- a/net/9p/trans_fd.c
> +++ b/net/9p/trans_fd.c
> @@ -231,7 +231,7 @@ static void p9_conn_cancel(struct p9_conn *m, int err)
>  static __poll_t
>  p9_fd_poll(struct p9_client *client, struct poll_table_struct *pt, int *err)
>  {
> -	__poll_t ret, n;
> +	__poll_t ret;
>  	struct p9_trans_fd *ts = NULL;
>  
>  	if (client && client->status == Connected)
> @@ -243,19 +243,9 @@ p9_fd_poll(struct p9_client *client, struct poll_table_struct *pt, int *err)
>  		return EPOLLERR;
>  	}
>  
> -	if (!ts->rd->f_op->poll)
> -		ret = DEFAULT_POLLMASK;
> -	else
> -		ret = ts->rd->f_op->poll(ts->rd, pt);
> -
> -	if (ts->rd != ts->wr) {
> -		if (!ts->wr->f_op->poll)
> -			n = DEFAULT_POLLMASK;
> -		else
> -			n = ts->wr->f_op->poll(ts->wr, pt);
> -		ret = (ret & ~EPOLLOUT) | (n & ~EPOLLIN);
> -	}
> -
> +	ret = vfs_poll(ts->rd, pt);
> +	if (ts->rd != ts->wr)
> +		ret = (ret & ~EPOLLOUT) | (vfs_poll(ts->wr, pt) & ~EPOLLIN);
>  	return ret;
>  }
>  
> diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
> index 6e865e8b5b10..90d30fbe95ae 100644
> --- a/virt/kvm/eventfd.c
> +++ b/virt/kvm/eventfd.c
> @@ -397,7 +397,7 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
>  	 * Check if there was an event already pending on the eventfd
>  	 * before we registered, and trigger it as if we didn't miss it.
>  	 */
> -	events = f.file->f_op->poll(f.file, &irqfd->pt);
> +	events = vfs_poll(f.file, &irqfd->pt);
>  
>  	if (events & EPOLLIN)
>  		schedule_work(&irqfd->inject);
> -- 
> 2.14.2
> 

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