NetBSD Problem Report #51080

From www@NetBSD.org  Wed Apr 20 22:18:48 2016
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Date: Wed, 20 Apr 2016 22:18:46 +0000 (UTC)
From: pablo@polvorin.com.ar
Reply-To: pablo@polvorin.com.ar
To: gnats-bugs@NetBSD.org
Subject: Support pvfb on xen domu (patch)
X-Send-Pr-Version: www-1.0

>Number:         51080
>Category:       port-xen
>Synopsis:       Support pvfb on xen domu (patch)
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    port-xen-maintainer
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Wed Apr 20 22:20:00 +0000 2016
>Last-Modified:  Sat Jun 25 17:30:00 +0000 2016
>Originator:     Pablo Polvorin
>Release:        7.0
>Organization:
>Environment:
>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


There is a little bit more description at http://blog.polvorin.com.ar/2016/04/20/netbsd-pvfb.html 






>How-To-Repeat:

>Fix:
above patch

>Audit-Trail:
From: Manuel Bouyer <bouyer@antioche.eu.org>
To: gnats-bugs@NetBSD.org
Cc: port-xen-maintainer@netbsd.org, gnats-admin@netbsd.org,
        netbsd-bugs@netbsd.org
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 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>
      NetBSD: 26 ans d'experience feront toujours la difference
 --

From: Pablo Polvorin <pablo@polvorin.com.ar>
To: gnats-bugs@NetBSD.org
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> wrote:

 > The following reply was made to PR port-xen/51080; it has been noted
 > by GNATS.
 > 
 > From: Manuel Bouyer <bouyer@antioche.eu.org>
 > To: gnats-bugs@NetBSD.org
 > Cc: port-xen-maintainer@netbsd.org, gnats-admin@netbsd.org,
 >         netbsd-bugs@netbsd.org
 > 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
 > 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>
 >       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.

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