From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752908AbbJEUCk (ORCPT ); Mon, 5 Oct 2015 16:02:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59281 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751253AbbJEUCj (ORCPT ); Mon, 5 Oct 2015 16:02:39 -0400 Date: Mon, 5 Oct 2015 23:02:32 +0300 From: "Michael S. Tsirkin" To: Vlad Zolotarov Cc: Greg KH , linux-kernel@vger.kernel.org, hjk@hansjkoch.de, corbet@lwn.net, bruce.richardson@intel.com, avi@cloudius-systems.com, gleb@cloudius-systems.com, stephen@networkplumber.org, alexander.duyck@gmail.com Subject: Re: [PATCH v3 1/3] uio: add ioctl support Message-ID: <20151005225157-mutt-send-email-mst@redhat.com> References: <1443991398-23761-1-git-send-email-vladz@cloudius-systems.com> <1443991398-23761-2-git-send-email-vladz@cloudius-systems.com> <20151005030352.GA27303@kroah.com> <561227C0.5050607@cloudius-systems.com> <20151005080149.GB1747@kroah.com> <561252B3.4000406@cloudius-systems.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <561252B3.4000406@cloudius-systems.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 05, 2015 at 01:36:35PM +0300, Vlad Zolotarov wrote: > >And then there's the issue of why we even need this, why not just > >write a whole new driver for this, like the previous driver did (which > >also used ioctls, yes, I didn't have the chance to object to that before > >everyone else did...) > > Which "previous driver" do u refer here? > IMHO writing something instead of UIO (not just uio_pci_generic) seems like > an overkill for solving this issue. Supporting MSI-X interrupts seem like a > very beneficial feature for uio_pci_generic and it's really not _THAT_ > complicated API - just look at VFIO for a comparison... ;) Except most things VFIO does is actually there for security. Which, for a device that can do DMA and isn't even behind an IOMMU, sounds like a pretty big deal actually. > uio_pci_generic is clearly missing this important feature. And creating > another user space driver infrastructure just to add it seems extremely > unjustified. uio_pci_generic was always intended to be used with extremely simple devices which don't do DMA, or where someone else has set up the IOMMU (like kvm does with CONFIG_KVM_DEVICE_ASSIGNMENT). We need to be much more careful with MSI if there's no IOMMU. -- MST