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

[Pablo Polvorin <pablo%polvorin.com.ar@localhost>]

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

From: Pablo Polvorin <pablo%polvorin.com.ar@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: port-xen/51080: Support pvfb on xen domu (patch)
Date: Sat, 25 Jun 2016 14:31:09 -0300

 On Thu, 19 May 2016 09:20:01 +0000 (UTC)
 Manuel Bouyer <bouyer%antioche.eu.org@localhost> wrote:
 
 > The following reply was made to PR port-xen/51080; it has been noted
 > by GNATS.
 > 
 > From: Manuel Bouyer <bouyer%antioche.eu.org@localhost>
 > To: gnats-bugs%NetBSD.org@localhost
 > Cc: port-xen-maintainer%netbsd.org@localhost, gnats-admin%netbsd.org@localhost,
 >         netbsd-bugs%netbsd.org@localhost
 > 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, pablo%polvorin.com.ar@localhost
 > wrote:
 >  > >Description:  
 >  > The patch is available here
 >  > http://blog.polvorin.com.ar/patches/pvfb.patch
 >  > 
 >  > is an attempt at supporting the virtual framebuffer on xen guest
 >  > ( http://wiki.netbsd.org/projects/project/xen-domu-pvfb/ )
 >  > 
 >  > 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  
 >  
 >  Hello,
 >  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 <bouyer%antioche.eu.org@localhost>
 >       NetBSD: 26 ans d'experience feront toujours la difference
 >  --
 >  
 
 Hello, thanks for your comments and sorry for the delay, I've been very
 busy. Will probably be able to work on this again in ~1 week.
 
 Yes AFAIK linux uses command line/user-space tools for configuring the
 resolution (the xen framebuffer plugs into a general fb framework
 that already has the callbacks defined for that). 
 I'll use your hint about the kernel command line, it will be a usable
 workaround that shouldn't require much change.
 
 >  Are you sure the framebuffer has a protocol entry in the xenstore ?
 >  If not, you should probably remove it from xfb_xenbus_resume().
 I can't find documentation about it now, but it's on the linux driver, I
 probably just copied that from there.
 
 >  Are you sure it's not some uninitialised variable ?
 No I'm not :) . Will try to review that again.