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: <201004280003.31668.rjw@sisk.pl>
Date:	Wed, 28 Apr 2010 00:03:31 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>,
	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 Tuesday 27 April 2010, Alan Stern wrote:
> 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.

In the meantime, though, I thought that the suspend blocker might be created
by _open() if we found a way to automatically choose a name for it.  That'd be
kind of logical, since it's later destroyed by _release().

So, what about using the name of the process that opened the special device
file (or that name with'0' appended, or generally with a number appended) as
the suspend blocker name?

Rafael
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