XendBootLoader.py:
- 判读bootloader是否存在
- Linux:/usr/bin/pygrub
- Windows: /usr/lib/xen/boot/hvmloade
- 判断 启动设备是否存在,不存在返回:Disk isn't accessible
- 打开一个管道,用于两个pty进程间通信:/var/run/xend/boot/xenbl.%s
- 构造命令并在pty子进程中执行:
- /usr/bin/pygrub [ --kernel=%s --ramdisk=%s --args=%s --output=%s -q ] path-to-disk
- 如果子进程(执行bootloader)执行失败,或没有任何输出,则raise VmError, msg,否则返回sxp格式的结果。
源码中的注释:
# We need to present the bootloader's tty as a pty slave that xenconsole
# can access. Since the bootloader itself needs a pty slave,
# we end up with a connection like this:
#
# xenconsole -- (slave pty1 master) <-通过管道复制数据-> (master pty2 slave) -- bootloader
#
# where we copy characters between the two master fds, as well as
# listening on the bootloader's fifo for the results.
# filedescriptors:
# r - input from the bootloader (bootstring output)
# m1 - input/output from/to xenconsole
# m2 - input/output from/to pty that controls the bootloader
# r - input from the bootloader (bootstring output)
# m1 - input/output from/to xenconsole
# m2 - input/output from/to pty that controls the bootloader
/usr/bin/pygrub
pygrub解析传入的分区的结构,如果是一个disk,那么就从disk找到active的分区,如果是分区,那就直接解析分区,然后引导启动。
Usage: /usr/bin/pygrub [-q|--quiet] [-i|--interactive] [--output=] [--kernel=] [--ramdisk=] [--args=] [--entry=] <image>
- grub文件路径为:/boot/grub/menu.lst", "/boot/grub/grub.conf" 或 "/grub/menu.lst", "/grub/grub.conf"
- 使用pygrub,启动分区要放在第一个位置。
手动执行的结果是:
linux (kernel /var/run/xend/boot/boot_kernel.L_jphs)(ramdisk /var/run/xend/boot/boot_ramdisk.9Ed02z)(args "ro root=/dev/sda2 ")
PV-GRUB被认为是pygrub的取代:
PV-GRUB replaces PyGrub to boot domU images safely: it runs the regular grub inside the created domain itself and uses regular domU facilities to read the disk / fetch files from network etc.; it eventually loads the PV kernel and chain-boots it.
kernel = "/usr/lib/xen/boot/pv-grub-x86_32.gz"
extra = "(hd0,0)/grub/menu.lst"
/usr/lib/xen/boot/hvmloader
源码在hvmloader.c中,有待继续研究。