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

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Date:	Tue, 27 Apr 2010 16:22:11 -0700
From:	Arve Hjønnevåg <arve@...roid.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	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

2010/4/27 Rafael J. Wysocki <rjw@...k.pl>:
> 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?
>

I prefer to let user space choose the name since we use more than one
suspend blocker in the same process.

-- 
Arve Hjønnevåg
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