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

From: Alan Stern
Date: Tue May 15 2012 - 12:03:57 EST

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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