RE: [Xen-devel] Trying fbcon in dom1,but take_over_console fails...

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> > I suspect you'd be better off getting the xencons to 
> register as ttyS0
> > (xencons=ttyS0) so that it doesn't go anywhere near the 
> console, and 
> > compile in  VT, VT_CONSOLE and DUMMY_CONSOLE.
> Tried that, as well as disabling VGA_CONSOLE, but no 
> improvements :-(:-( however, when built as a module, it is 
> somewhat easier to debug this problem in fbcon, since dom1 is 
> still running after it segfaults, and I can still use dmesg 
> to see the printk's (strange that they don't appear on the 
> console...).

Do you actually need fbcon? You don't need it to run X in most setups.

[If you want the printk's to come out on the console, use the KERN_ALERT prefix]


Ian

> >
> > Please let us know how you get on.
> 
> Ok, here's what I found so far:
> 
> Using printk statements, I was able to find the culprit, it 
> seems to be the vc pointer which is not initialised properly.
> 
> Here's the piece of code (from fbcon_startup):
> 
>         /* Setup default font */
>         if (!p->fontdata) {
>                 if (!fontname[0] || !(font = find_font(fontname)))
>                         font = get_default_font(info->var.xres,
>                                                 info->var.yres);
> 
>                 DPRINTK("fbcon_startup: ca\n");
> 
>                 vc->vc_font.width = font->width;
>                 vc->vc_font.height = font->height;
>                 vc->vc_font.data = p->fontdata = font->data;
>                 vc->vc_font.charcount = 256; /* FIXME  Need 
> to support more fonts */
> 
>                 DPRINTK("fbcon_startup: cb\n");
> 
>         }
> 
> And the oops occurs between the two DPRINTK's...
> So I added a check at startup:
> 
> static const char *fbcon_startup(void)
> {
>         const char *display_desc = "frame buffer device";
>         struct display *p = &fb_display[fg_console];
>         struct vc_data *vc = vc_cons[fg_console].d;
>         struct font_desc *font = NULL;
>         struct module *owner;
>         struct fb_info *info = NULL;
>         struct fbcon_ops *ops;
>         int rows, cols;
>         int irqres;
> 
>         DPRINTK("fbcon_startup... fg_console: %d, vc: 
> %d\n",fg_console,vc);
> 
> This prints 0 for the fg_console (not necessarely a problem) 
> as well as vc... 
> which is defenately a problem since it is dereferenced later!
> 
> Seems like the vc_cons is not setup right, I'll have to take 
> a look into vt.c I guess.
> Could this be due to the missing ps/2 port on domU (since 
> they are assigned to dom0)?
> 
> Will report back when I know more.
> 
> 
> Regards,
> Mark.
> 
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> http://lists.xensource.com/xen-devel
> 

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