From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754100AbcGHIb7 (ORCPT ); Fri, 8 Jul 2016 04:31:59 -0400 Received: from mail-lf0-f67.google.com ([209.85.215.67]:32875 "EHLO mail-lf0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751692AbcGHIbx (ORCPT ); Fri, 8 Jul 2016 04:31:53 -0400 Reply-To: alex.popov@linux.com Subject: Re: [PATCH 1/1] irqdomain: Export __irq_domain_alloc_irqs() and irq_domain_free_irqs() References: <1467401388-11221-1-git-send-email-alex.popov@linux.com> To: Thomas Gleixner Cc: Marc Zyngier , LKML , Alexander Popov From: Alexander Popov Message-ID: <577F6578.6030904@linux.com> Date: Fri, 8 Jul 2016 11:34:00 +0300 User-Agent: Mozilla/5.0 (X11; Linux i686; rv:38.0) Gecko/20100101 Thunderbird/38.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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