[PATCH kexec-tools] x86: use old screen_info if needed

[Simon Horman]

On Mon, Jan 29, 2018 at 03:59:54PM +0800, Dave Young wrote:
> On 01/29/18 at 08:21am, Simon Horman wrote:
> > On Sun, Jan 28, 2018 at 01:52:31PM +0800, Dave Young wrote:
> > > With modern drm/kms graphic driver kexec-tools does not setup screen_info
> > > correctly so one will only see screen output after those drm drivers
> > > reinitializing after rebooting. Copying the old screen info from original
> > > boot_params will help during my test, although it could not work for some
> > > potential cases, but it is not worse than before.  This has been used in
> > > the kernel kexec_file_load.
> > > 
> > > Signed-off-by: Dave Young <dyoung at redhat.com>
> > 
> > Thanks, applied.
> 
> Hi Simon,
> 
> Thanks for taking it.  I tested the original version on my laptop with
> efi boot.  either of below two changes work for me:
> 
> a) use the setup_linux_vesafb() detected values and change the orig_video_isVGA
> to 0x70 (copy from boot params)
> 
> b) copy all screen_info from boot params.
> 
> I actually was hesitating which one is better and finally I sent the b).
> But maybe a) + b) will be better, since my case is a framebuffer, I'm
> not sure non-framebuffer case though it will be not worse with the
> patch.  Could you consider an appending patch below?

Sure, sorry for being a bit hasty.

I've appended the change below.
> 
> ---
> In current kexec-tools we have already vesafb detecting code,
> but in case unsupported vesa fb types it just return and do nothing
> During my test copying the old boot time screen info works for me with
> efi booted machine. And the vesa fb detected values also work even if the
> fb fix.id is "inteldrmfb", thus change the code to use those values
> detected with fb ioctl first for framebuffer systems.
> 
> Signed-off-by: Dave Young <dyoung at redhat.com>
> ---
>  kexec/arch/i386/x86-linux-setup.c |   10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> --- kexec-tools.orig/kexec/arch/i386/x86-linux-setup.c
> +++ kexec-tools/kexec/arch/i386/x86-linux-setup.c
> @@ -123,6 +123,7 @@ void setup_linux_bootloader_parameters_h
>  	cmdline_ptr[cmdline_len - 1] = '\0';
>  }
>  
> +static int get_bootparam(void *buf, off_t offset, size_t size);
>  static int setup_linux_vesafb(struct x86_linux_param_header *real_mode)
>  {
>  	struct fb_fix_screeninfo fix;
> @@ -144,8 +145,13 @@ static int setup_linux_vesafb(struct x86
>  		/* VIDEO_TYPE_EFI */
>  		real_mode->orig_video_isVGA = 0x70;
>  	} else {
> -		/* cannot handle and other types */
> -		goto out;
> +		int err;
> +		off_t offset = offsetof(typeof(*real_mode), orig_video_isVGA);
> +
> +		/* blindly try old boot time video type */
> +		err = get_bootparam(&real_mode->orig_video_isVGA, offset, 1);
> +		if (err)
> +			goto out;
>  	}
>  	close(fd);
>  
>