Re: [PATCH qemu-kvm] device-assignment: add config fd qdev property

["Daniel P. Berrange" <berrange@redhat.com>]

On Wed, May 19, 2010 at 02:18:35PM -0500, Anthony Liguori wrote:
> On 05/19/2010 02:00 PM, Chris Wright wrote:
> >When libvirt launches a guest it first chowns the relevenat
> >/sys/bus/pci/.../config file for an assigned device then drops privileges.
> >
> >This causes an issue for device assignment because despite being file
> >owner, the sysfs config space file checks for CAP_SYS_ADMIN before
> >allowing access to device dependent config space.
> >
> >This adds a new qdev configfd property which allows libvirt to open the
> >sysfs config space file and give qemu an already opened file descriptor.
> >Along with a change pending for the 2.6.35 kernel, this allows the
> >capability check to compare against privileges from when the file was
> >opened.
> >
> >Signed-off-by: Chris Wright<chrisw@redhat.com>
> >   
> 
> An fd as a qdev property seems like a bad idea to me.  I'm not sure I 
> have a better suggestion though.

The entire requirement to pass the open FD to qemu is a bad idea, but
the kernel makes it impossible to do otherwise :-( Personally I wish the
kernel just used the file ownership, so we could chown() the sysfs file 
to 'qemu' user in a normal manner :-(

Daniel
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