linux-kernel - Re: [PATCH 03/31] fs: introduce new ->get_poll_head and ->poll

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Message-ID: <20180108104513.GB5797@lst.de>
Date:   Mon, 8 Jan 2018 11:45:13 +0100
From:   Christoph Hellwig <hch@....de>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     Christoph Hellwig <hch@....de>, Avi Kivity <avi@...lladb.com>,
        linux-aio@...ck.org, linux-fsdevel@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/31] fs: introduce new ->get_poll_head and
        ->poll_mask methods

On Sat, Jan 06, 2018 at 07:12:42PM +0000, Al Viro wrote:
> On Thu, Jan 04, 2018 at 09:00:15AM +0100, Christoph Hellwig wrote:
> > ->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.
> 
> *UGH*
> 
> Gotta love the optimism, but have you actually done the conversion?
> I'm particularly suspicious about the locking rules here...

I've done just about everything but random drivers.  Which is the ones
where people care about performance and thus aio poll.  I suspect that
we will have various odd cruft drivers that will be left alone.