linux-kernel - Re: [PATCH] uio: add irq control support to uio_pci

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Date:	Thu, 16 Apr 2015 14:21:10 -0700
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	"Hans J. Koch" <hjk@...sjkoch.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] uio: add irq control support to uio_pci_generic

On Thu, 16 Apr 2015 09:43:24 +0200
"Michael S. Tsirkin" <mst@...hat.com> wrote:

> On Wed, Apr 15, 2015 at 09:59:34AM -0700, Stephen Hemminger wrote:
> > The driver already supported INTX interrupts but had no in kernel
> > function to enable and disable them.
> > 
> > It is possible for userspace to do this by accessing PCI config
> > directly, but this racy
> 
> How is it racy? We have userspace using this interface,
> if there's a race I want to fix it.

There is nothing to prevent two threads in user space doing 
read/modify write at the same time.

The bigger issue is that DPDK needs to support multiple UIO
interface types. And with current model there is no abstraction.
The way to enable/disable IRQ is different depending on the UIO
drivers.
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