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

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Date:	Fri, 8 Jul 2016 11:34:00 +0300
From:	Alexander Popov <alex.popov@...ux.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Marc Zyngier <marc.zyngier@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Alexander Popov <alex.popov@...ux.com>
Subject: Re: [PATCH 1/1] irqdomain: Export __irq_domain_alloc_irqs() and
 irq_domain_free_irqs()

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?

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.

Best regards,
Alexander