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Re: [Xen-devel] console: introduce console=none option

On Thu, 2012-01-26 at 16:00 +0000, Jan Beulich wrote:
> >>> On 26.01.12 at 15:58, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> > On 26/01/12 14:41, Jan Beulich wrote:
> >>>>> On 26.01.12 at 13:19, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> >>> XenServer by default boots without a serial console (buggy hardware
> >>> reasons) and dom0 displays a splash screen.  Unfortunately, having Xen
> >>> writing to the vga text area looks ugly whilst dom0 is trying to set up
> >>> non-text mode and display  the splash screen.
> >>>
> >>> We have been using "console=" to prevent this behavior for a while, but
> >>> presented herewith is a patch to fix the problem correctly.
> >> While I don't mind the patch, I'm completely confused by the description:
> >> Where is it that Xen writes to VGA text area after control was passed to
> >> Dom0?
> >>
> >> Jan
> > 
> > I have not debugged it that much as I was looking for a clean solution
> > to our current hack of "console=" (and I have some rather more serious
> > deadlock bugs to debug), but it all Xen printk's are going into the VGA
> > text area, even after dom0 has started.  It is possible that Xen is
> > still writing into the text area after dom0 has switched VGA mode, but I
> > have no proof of this one way or the other.
> Just take a look at vga_endboot() - the output routine gets pointed to
> vga_noop_puts() unless vgacon_keep. Beyond that point nothing
> can possibly get printed to the VGA text screen, or if it does, then I'd
> suspect there's some other change in XenServer that makes it so.

IIRC the original purpose of this patch was to stop Xen from displaying
anything at all on the VGA, not just after dom0 handover but right from
start of day.

This was so that the splash screen (placed by the bootloader) didn't get
overwritten until dom0 comes up and takes over with the boot progress
meter thing.

Maybe that's changed in the meantime but that's my recollection.


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