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Re: port-xen/51080: Support pvfb on xen domu (patch)

The following reply was made to PR port-xen/51080; it has been noted by GNATS.

From: Manuel Bouyer <>
Subject: Re: port-xen/51080: Support pvfb on xen domu (patch)
Date: Thu, 19 May 2016 11:17:36 +0200

 On Wed, Apr 20, 2016 at 10:20:00PM +0000, wrote:
 > >Description:
 > The patch is available here
 > is an attempt at supporting the virtual framebuffer on xen guest
 > ( )
 > Basic functionality is in place, but reached a point where guidance/feedback would be very welcome in order to push this forward,
 > this is the first piece of kernel code I attempt to write, and I'm not
 > that familiar with netbsd to start with.
 > Need to review, at least
 > * Memory management (conversion to frame number to pass references to xen host).  Currently save/restore isn't working,  but neither do it  without this patch on my install.
 > * code just act as a kind of adapter between xenbus and genfb, wskbddev and wsmousedev, letting them attach to xenbus. Is that the way to go?
 > * The way I added the drivers to be used by autoconf
 this looks good, good work !
 For the framebuffer resolution/depth, how does linux do ? Is it something it
 gets from the domU config file via the store ? Or via the command line ?
 AFAIK NetBSD's genfb doens't have a way to change the resolution from userland.
 If there's no provision to set the parameters in the xenstore you could pass
 it from the kernel command line, e.g. xenfb=1280x1024x32
 This will have to be parsed in xen_parse_cmdline(), which then can be called
 from xfb_xenbus.c.
 Are you sure the framebuffer has a protocol entry in the xenstore ?
 If not, you should probably remove it from xfb_xenbus_resume().
 For the race condition you mention in xfb_xenbus_attach() I don't understant
 how it can happens. The
 genfb framebuffer at 0xffff,  size  , depth,  stride
 line should always be there.
 Are you sure it's not some uninitialised variable ?
 Manuel Bouyer <>
      NetBSD: 26 ans d'experience feront toujours la difference

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