netdev - Re: [PATCH 02/31] fs: add new vfs_poll and file_can

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Date:   Mon, 8 Jan 2018 11:44:19 +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 02/31] fs: add new vfs_poll and file_can_poll helpers

On Sat, Jan 06, 2018 at 07:08:53PM +0000, Al Viro wrote:
> On Thu, Jan 04, 2018 at 09:00:14AM +0100, Christoph Hellwig wrote:
> > These abstract out calls to the poll method in preparation for changes to
> > those methods.
> 
> FWIW, I would make vfs_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);
> }
> 
> That's safe for any struct file, some of the callers already do just that,
> the ones that have vfs_poll() under the check for file_can_poll() will
> simply optimize that piece away and the few that rely upon the knowledge
> of file_operations they are dealing with (vhost, etc.) can bloody well
> cope with the cost of the check.

Sure, works for me.