linux-kernel - Re: [PATCH 0/8] introduce dynamic device creation/removal

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Message-ID: <20150302141805.6e0ed07a@www.etchedpixels.co.uk>
Date:	Mon, 2 Mar 2015 14:18:05 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Minchan Kim <minchan@...nel.org>,
	Jerome Marchand <jmarchan@...hat.com>,
	Nitin Gupta <ngupta@...are.org>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/8] introduce dynamic device creation/removal

> > This is a long term plan, of course, but I'd like to see sysfs functions go away
> > in a year or so. What do you think?
> 
> hoo boy.  Creating a /dev node and doing ioctls on it is really old
> school.  So old school that I've forgotten why we don't do it any more.
> 
> Hopefully Alan can recall the thinking?

Gee.. pass me the walking stick and the pipe !

The problem we used to have with it was re-use of /dev nodes and
permissions. For example if I create a ZRAM instance and then we crash
and my /dev is persistent then next boot I can potentially be opening
that left over node (or it may even be forgotten), which has old and
stale permissions on it.

With devtmpfs it's a bit easier and saner.

The old abuser of this was the old PCMCIA layer which has more exciting
versions of the problem as it used /tmp for some nodes.

Switching to sysfs probably fits better but the problem is the generic
one of revoking access rights to an object.

Alan
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