linux-kernel - RE: [PATCH 15/77] Staging: hv: blkvsc: Add the appropriate MODULE

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Date:	Wed, 6 Jul 2011 15:17:37 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Greg KH <greg@...ah.com>
CC:	"gregkh@...e.de" <gregkh@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"virtualization@...ts.osdl.org" <virtualization@...ts.osdl.org>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	"Hank Janssen" <hjanssen@...rosoft.com>
Subject: RE: [PATCH 15/77] Staging: hv: blkvsc: Add the appropriate
 MODULE_ALIAS() line



> -----Original Message-----
> From: Greg KH [mailto:greg@...ah.com]
> Sent: Wednesday, July 06, 2011 11:02 AM
> To: KY Srinivasan
> Cc: gregkh@...e.de; linux-kernel@...r.kernel.org;
> devel@...uxdriverproject.org; virtualization@...ts.osdl.org; Haiyang Zhang; Hank
> Janssen
> Subject: Re: [PATCH 15/77] Staging: hv: blkvsc: Add the appropriate
> MODULE_ALIAS() line
> 
> On Wed, Jul 06, 2011 at 02:55:12PM +0000, KY Srinivasan wrote:
> > > > I think you mean MODULE_DEVICE_TABLE()?
> > >
> > > Yes, sorry for the typo.
> > >
> > > > I actually went down that path first
> > > > adding code  to  file2alias.c for parsing the vmbus ID table. Given that this
> > > approach
> > > > would make it  impossible to support auto-loading of these drivers
> > > > on many of the released kernels,
> > >
> > > Wait, what?  What is a "released kernel"?  We are working on the
> > > in-kernel patch, we don't care about older distros/releases for this
> > > work at all.  Also, it doesn't make sense at all, why would the change I
> > > asked for make any difference on older distros/kernels?
> >
> > I understand we don't care here about older kernels and I will do what you
> > have suggested. I just wanted to give you the rationale for choices I made:
> > We are currently supporting older distros/kernels using these upstream bits.
> > With the MODULE_ALIAS() approach, since I did not have to change any code
> > outside the hv directory, this was possible. I was mostly concerned about
> > having to make changes to code outside the hv directory and figuring out
> > how to build and propagate these changes (file2alias.c) in older kernels.
> 
> You create a patch like any other patch and give it to the people who
> are stuck with those older kernels.  It shouldn't be that hard, and it
> also shouldn't be something that matters for this mainline work either.
> 
> > > > I chose to go with the MODULE_ALIAS() macro that did not need any
> > > > changes outside our drivers. In both methods, the formatting of the
> > > > name is bus specific since I would be writing the code to parse the
> > > > table in file2alias.c.
> > >
> > > Yes, that is what is needed to be done.
> > >
> > > > Granted, I have been quite unimaginative in my alias names, but I
> > > > thought they were reasonably descriptive. If at all possible, for the
> > > > reasons listed above, I would prefer to use the MODULE_ALIAS() macro
> > > > (I could embed all or part of the guid in the alias). Let me know.
> > >
> > > Please do the correct thing and use MODULE_DEVICE_TABLE().
> >
> > We have four drivers now excluding vmbus and soon we will have only three
> > drivers with the merge of block and stor drivers. Would you still recommend I
> use the
> > full guid to name these drivers.
> 
> Yes, why not?
> 
> > Rather than embedding the entire 128bit guid in module aliases, I was
> > thinking of setting up a more reasonable namespace for these drivers
> > (like what virtio has done for instance). Let me know if this is ok
> > with you if I took that route (mapping the guid to small integers and
> > having these integers be used in alias strings).
> 
> What's the big deal of having a large number as an alias?  Is there some
> constraint here that I am not aware of?

It is certainly easier to deal with a small integer than with 128bit giud and there is
no added benefit dealing with guids since the number of drivers we will support
under vmbus will never exceed a very small number. Having said that, I will go ahead
and embed full guids as you have suggested. So, the aliases for these drivers will be:
vmbus:device guid.

Regards,

K. Y

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