linux-kernel - Re: [PATCH] video4linux: Push down the BKL

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Date:	Fri, 23 May 2008 16:39:56 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	corbet@....net (Jonathan Corbet)
Cc:	video4linux-list@...hat.com, linux-kernel@...r.kernel.org,
	mchehab@...radead.org
Subject: Re: [PATCH] video4linux: Push down the BKL

> On the other hand, the next level of BKL pushdown would be painful as
> all hell, given the massive number of callbacks in the V4L2 API.  So I'm
> thinking it might be justified to create a video_ioctl2_locked() for
> V4L2 drivers which are not yet known to be safe in the absence of the
> BKL.  The amount of extra code would be quite small, and it would let
> safe drivers operate BKL-free.

The problem is that currently they are almost all unsafe - I did a quick
survey as part of the changes. Pushing it down to the video2_ioctl is a
starting point, but the v4l layer is going to need a lot of love and its
own gradual migration.

Right now we've gone from BKL buried in fs to BKL at top of v4l layer
which is indeed only a starting point. I'd assumed the same as you are
think a new video_ioctl2 and switching drivers one by one (I was assuming
adding video2_ioctl_unlocked())

Alan
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