linux-kernel - Re: [PATCH V3 2/4] scsi: storvsc: Properly support Fibre Channel devices

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Date:	Fri, 18 Dec 2015 09:13:40 -0800
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Hannes Reinecke <hare@...e.de>,
	"K. Y. Srinivasan" <kys@...rosoft.com>, gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org, devel@...uxdriverproject.org,
	ohering@...e.com, jbottomley@...allels.com, hch@...radead.org,
	linux-scsi@...r.kernel.org, apw@...onical.com, vkuznets@...hat.com,
	jasowang@...hat.com, martin.petersen@...cle.com
Subject: Re: [PATCH V3 2/4] scsi: storvsc: Properly support Fibre Channel
 devices

On Fri, 2015-12-18 at 09:49 +0100, Hannes Reinecke wrote:
> What I would like to see is a clear separation here:
> - Disable FC disk handling if FC attributes are not configured
> - Add a module parameter allowing to disable FC attributes even if 
> they are compiled in. Remember: this is a virtualized guest, and 
> people might want so save kernel memory wherever they can. So always 
> attaching to the fc transport template will make them very unhappy.
> Alternatively you could split out FC device handling into a separate 
> driver, but seeing the diff that's probably overkill.

I don't quite see how this can be a module parameter: the
fc_transport_class is pulled in by symbol references.  They won't go
away whether a module parameter is zero or one.  The only way to get
the module not to link with a transport class is to have it not use the
symbols at compile time (either because they're surrounded by an #ifdef
or with an if() which the compiler evaluates at compile time to zero). 
 In userspace you get around this with introspection and dlopen, but I
don't think we have that functionality in the kernel.

James

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