linux-kernel - Re: [PATCH 1/1] irqdomain: Export __irq_domain_alloc_irqs() and irq_domain_free

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Message-ID: <20160716092218.3a2de5c7@arm.com>
Date:	Sat, 16 Jul 2016 09:22:18 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Alexander Popov <alex.popov@...ux.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] irqdomain: Export __irq_domain_alloc_irqs() and
 irq_domain_free_irqs()

On Sat, 16 Jul 2016 04:33:59 +0300
Alexander Popov <alex.popov@...ux.com> wrote:

> On 08.07.2016 11:34, Alexander Popov wrote:
> > On 06.07.2016 14:17, Thomas Gleixner wrote:  
> >> On Fri, 1 Jul 2016, Alexander Popov wrote:
> >>  
> >>> Export __irq_domain_alloc_irqs() and irq_domain_free_irqs() for being
> >>> able to work with irq_domain hierarchy in modules.  
> >>
> >> We usually export only when we have a proper use case which is supposed to go
> >> into the kernel tree proper. What's yours?  
> > 
> > Hello, Thomas,
> > 
> > I work at Positive Technologies ( https://www.ptsecurity.com/ ). We develop
> > a bare-metal hypervisor, which targets x86_64 and supports Linux as a guest OS.
> > 
> > Intel VT-x allows hypervisor to inject interrupts into virtual machines.
> > We want to handle these interrupts in guest Linux.
> > 
> > So I wrote a simple kernel module creating an irq_domain, which has
> > x86_vector_domain as a parent in the hierarchy. In this module I just call:
> > - irq_domain_alloc_irqs() to allocate irqs and allow calling request_irq()
> >    for them;
> > - irqd_cfg(irq_get_irq_data()) to get the APIC vectors of the allocated irqs;
> > - irq_domain_free_irqs() to free the resources at the end.
> > 
> > It allows to handle interrupts injected by the hypervisor in guest Linux easily,
> > without emulating MSI-capable PCI device at the hypervisor side.
> > 
> > Everything works fine if __irq_domain_alloc_irqs() and irq_domain_free_irqs()
> > are exported. Is it a proper use-case?  
> 
> Hello again, Thomas,
> 
> Did I properly answer your question? Will you accept my patch exporting these
> two functions?
> 
> > Do you think my module could be useful for the mainline in some form?
> > It took me some time to understand irq_domain hierarchy design, so I can
> > prepare some patch or share my code to help others.  
> 
> Do you think my paravirtualization code registering a child irq_domain
> for x86_vector_domain could bring any profit to the mainline?
> I would be glad to put effort and do it.

I think that without any in-tree modular users of these symbols, the
incentive for exporting those is pretty low. I can't really say
anything about your particular use-case, but I'd really to see some
code before taking that kind of patch.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny.