linux-kernel - Re: UIO: missing resource mapping

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Message-ID: <20120712234011.GE2592@local>
Date:	Fri, 13 Jul 2012 01:40:11 +0200
From:	"Hans J. Koch" <hjk@...sjkoch.de>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	"Hans J. Koch" <hjk@...sjkoch.de>,
	Andreas Schallenberg <embedded@....net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dominic Eschweiler <eschweiler@...s.uni-frankfurt.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	kvm@...r.kernel.org
Subject: Re: UIO: missing resource mapping

On Fri, Jul 13, 2012 at 02:16:32AM +0300, Michael S. Tsirkin wrote:
> On Thu, Jul 12, 2012 at 09:44:33PM +0200, Hans J. Koch wrote:
> > > Looking further at the code, I cannot see where the mem fields are
> > > being filled at all.
> > > Which code is supposed to write the struct uio_mem?
> > 
> > In my opinion, the driver should. However, Michael's idea is to use
> > /sys/bus/pci/devices/XXXXXresourceX for mapping purposes.
> > 
> > That is of course also possible, but obviously it leads to confusion.
> > We already had a long thread about this:
> > 
> > http://www.spinics.net/lists/kvm/msg73837.html
> > 
> > Michael, can we change the driver to offer all available PCI BARs in the
> > normal UIO way? I'm afraid otherwise we'll have the same discussion over
> > and over again.
> > 
> > Thanks,
> > Hans
> 
> My concern was people will ask for more and more stuff that pci
> sysfs already has.
> If we do add these is there a way to not duplicate code from pci?
> Export pci_mmap_resource and use it? Or make the uio attributes
> softlinks to pci sysfs somehow?

I understand your concern. Of course I'm also not in favor of duplicating
code, but I don't think there's much overhead. PCI already exports all
information needed by pci_resource_start(dev, bar) and
pci_resource_len(dev, bar). Have a look at other UIO PCI drivers like
uio_cif.c or uio_netx.c to see how it works. It's just a few more lines
of code to loop through all BARs and add the to info->mem[i].

By the way, the current size of the info->mem[] array was exactly made
with PCI in mind...

Thanks,
Hans

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