linux-kernel - Re: [RFC PATCH 1/3] block: add a flag to identify PM request

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Date:	Tue, 15 May 2012 12:03:56 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Lin Ming <ming.m.lin@...el.com>
cc:	Jens Axboe <axboe@...nel.dk>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Linux-pm mailing list <linux-pm@...r.kernel.org>,
	SCSI development list <linux-scsi@...r.kernel.org>
Subject: Re: [RFC PATCH 1/3] block: add a flag to identify PM request

On Tue, 15 May 2012, Lin Ming wrote:

> On Tue, 2012-05-15 at 10:35 -0400, Alan Stern wrote:
> > On Tue, 15 May 2012, Lin Ming wrote:
> > 
> > > Add a flag REQ_PM to identify the request is PM related.
> > > As an example, modify scsi code to use this flag.
> > 
> > There already is such a flag; you don't need to add one.  In fact, 
> > there already are _two_ such flags, and it would be best to remove one 
> > of them.  In include/linux/blkdev.h:
> > 
> > 	REQ_TYPE_PM_SUSPEND,		/* suspend request */
> > 	REQ_TYPE_PM_RESUME,		/* resume request */
> > 
> > Apparently they had been used by the old ide driver, but they don't
> > seem to be used anywhere now.
> 
> IDE code still uses both types and they are used for system
> suspend/resume. See generic_ide_suspend and generic_ide_resume.

You're right, of course.  I searched for "BLK_TYPE_PM_" instead of 
"REQ_TYPE_PM_".  :-(

> But we need a flag to check whether it is runtime suspend/resume
> request.

It should be possible to fix up the IDE code so that it uses the same
flag for both suspend and resume.  After all, there's no real danger of
confusion -- you never get into a situation where you're not sure
whether the current PM action is a suspend or a resume.

Alan Stern

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