Re: [PATCH 13/36] fs: introduce new ->get_poll_head and ->poll_mask methods

On Mon, Mar 19, 2018 at 08:29:38PM -0700, Darrick J. Wong wrote:

On Mon, Mar 05, 2018 at 01:27:20PM -0800, Christoph Hellwig wrote:

quoted

->get_poll_head returns the waitqueue that the poll operation is going
to sleep on.  Note that this means we can only use a single waitqueue
for the poll, unlike some current drivers that use two waitqueues for
different events.  But now that we have keyed wakeups and heavily use
those for poll there aren't that many good reason left to keep the
multiple waitqueues, and if there are any ->poll is still around, the
driver just won't support aio poll.

Signed-off-by: Christoph Hellwig <hch@lst.de>

I've been wondering, how does a regular filesystem connect with this?

In general, it doesn't.  In Unix regular files aren't pollable.

Also, does anything implement get_poll_head?  It looks to me like an aio
poll provider has to provide both...

Yes.  Everyone who implements ->poll_mask also needs to implement
get_poll_head.  For sockets we just happen to be able to use a generic
implementation in net/socket.c for most of them.

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