grub学习(3) 加载initrd

 

grub_err_t
grub_cmd_initrd (grub_command_t cmd __attribute__ ((unused)),
		 int argc, char *argv[])
{
	struct linux_kernel_header *lh;
	
	/* 打开initrd并计算其需要的页面 */
	file = grub_file_open (argv[0]);
	size = grub_file_size (file);
	initrd_pages = (page_align (size) >> 12);
	
	/* 计算initrd加载地址 */
	lh = (struct linux_kernel_header *) real_mode_mem;
	/* Get the highest address available for the initrd.  */
	if (grub_le_to_cpu16 (lh->version) >= 0x0203)
    {
      addr_max = grub_cpu_to_le32 (lh->initrd_addr_max);
    }
	addr_max -= 0x10000;

	/* Usually, the compression ratio is about 50%.  */
	addr_min = (grub_addr_t) prot_mode_target + ((prot_mode_pages * 3) << 12)
				+ page_align (size);

	/* Put the initrd as high as possible, 4KiB aligned.  */
	addr = (addr_max - size) & ~0xFFF;
	
	/* 分配空间 */
	grub_relocator_chunk_t ch;
    err = grub_relocator_alloc_chunk_align (relocator, &ch,
					    addr_min, addr, size, 0x1000,
					    GRUB_RELOCATOR_PREFERENCE_HIGH);
    initrd_mem = get_virtual_current_address (ch);
    initrd_mem_target = get_physical_target_address (ch);
	
	/* 读取initrd到缓存 */
	grub_file_read (file, initrd_mem, size) != size
	
	lh->ramdisk_image = initrd_mem_target;
	lh->ramdisk_size = size;
	lh->root_dev = 0x0100; 
}