linux-kernel - Re: [linux-pm] [PATCH 2/9] PM: suspend_block: Add driver to access suspend blockers from user-space

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Message-ID: <Pine.LNX.4.44L0.1004271432280.1850-100000@iolanthe.rowland.org>
Date:	Tue, 27 Apr 2010 14:33:23 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Arve Hjønnevåg <arve@...roid.com>
cc:	Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Magnus Damm <damm@...l.co.jp>,
	<linux-pm@...ts.linux-foundation.org>
Subject: Re: [linux-pm] [PATCH 2/9] PM: suspend_block: Add driver to access
  suspend blockers from user-space

On Mon, 26 Apr 2010, Arve Hjønnevåg wrote:

> > If you insist on using ioctl for init, you should use the standard
> > convention for passing variable-length data.  The userspace program
> > sets up a fixed-size buffer containing a pointer to the name and the
> > name's length, and it passes the buffer's address as the ioctl
> > argument.
> 
> Are you sure that is the standard? I searched for ioctls with NAME in
> their name and only found one that passed the name that way. The rest
> used fixed length string buffers, or passed the buffersize to _IOC
> like I do. For instance, input.h has ioctls to read string and
> bitmasks where user space specify the buffer size as an argument to
> the ioctl macro. These pass data from the kernel to user space, but I
> don't passing a string length is any worse than passing a buffer size.

You're right.  Okay, I withdraw my objection.

Alan Stern

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