Re: [Qemu-devel] [PATCH] set vidmode in linux kernel header when boot x86 using qemu bootloader

[Anthony Liguori]

Hi Joy,

joy zhao wrote:
> hi,
> I made a patch to have qemu parse vga field in kernel command line and 
> set the vid_mode field of real-mode kernel header.
> This patch is necessary because vga is one of the special command line 
> options that should be parsed in bootloader, as in linux kernel 
> Documentation/x86/i386/boot.txt. After bootloader write the passed vga 
> value into the vid_mode field of linux real-mode kernel header, this 
> vid_mode will be handled by linux/x86/boot/video.c in linux kernel to 
> select vesa graphics mode, and only in this mode can vesafb be 
> registered(in vesafb_probe()).
> So, if we decide to launch linux directly from qemu command line as 
> "qemu -kernel ... -initrd... -append "..." ", (use qemu bootloader) 
> and use vesafb as framebuffer driver, this patch to qemu is required, 
> otherwise, the screen should just blank since the vesafb fails to 
> register itself.
> Joy.
>
>  

Need a Signed-off-by: to apply this.

> diff --git a/qemu/hw/pc.c b/qemu-new/hw/pc.c
> index 66cc780..5615db8 100644
> --- a/qemu/hw/pc.c
> +++ b/qemu-new/hw/pc.c
> @@ -593,6 +593,77 @@ static long get_file_size(FILE *f)
>      return size;
>  }
>  
> +static uint16_t hato16i(char *hex)
> +{
> + uint16_t integer = 0;
> + if(hex[1] == 'x')
> +    hex += 2;
> +
> +    while(*hex != '\0'){
> +  integer = (integer<<4);
> +
> +  if(*hex >= 0x30 && *hex <= 0x39){ /*0~9*/
> +   integer += *hex - 0x30;
> +  }else if(*hex >= 0x61 && *hex <= 0x66){ /*a~f*/
> +   integer += *hex - 0x61 + 0xa;
> +  }else if(*hex >= 0x41 && *hex <= 0x46){ /*A~F*/
> +   integer += *hex - 0x41 + 0xa;
> +  }else
> +   break;
> +
> +  hex++;
> + } 
> + return integer;
> +}

Make sure you format according to CodingStyle.  Also, this function 
isn't needed as strtoul(hex, NULL, 16) provides the same functionality.

> +static uint16_t ato16i(char *dec)
> +{
> + uint16_t integer = 0;
> +
> +    while(*dec != '\0'){
> +  integer *= 10;
> +
> +  if(*dec >= 0x30 && *dec <= 0x39){ /*0~9*/
> +   integer += *dec - 0x30;
> +  }else
> +   break;
> +
> +  dec++;
> + } 
> + return integer;
> +}
> +static int get_vga_mode(const char* kernel_cmdline, uint16_t *vga_mode)
> +{
> + char mode[6];
> + int i = 0;
> + char *p = strstr(kernel_cmdline, "vga=");
> + if(p == NULL)
> +  return 1;
> +
> + p += 4;
> +
> + while(*p != ' ' && *p != '\0' && i < 6) {
> +  mode[i] = *p;
> +  i++;
> +  p++;  
> + }
> +
> + if(!strncmp(mode, "ask", 3)){
> +  *vga_mode = 0xfffd;
> + }else if(!strncmp(mode, "normal",6)){
> +  *vga_mode = 0xffff;
> + }else if(!strncmp(mode, "ext", 3)){
> +  *vga_mode = 0xfffe;
> + }else if(!strncmp(mode, "0x", 2)){//in hexdecimal
> +  *vga_mode = hato16i(mode);
> + }else //in decimal
> +  *vga_mode = ato16i(mode);

strtoul(mode, NULL, 0) will cover both hex and decimal.  You can check 
the value afterword to enforce u16 if you really want to.

Regards,

Anthony Liguori