The purpose of this patch is to allow the Xen hypervisor to pass extra data to GRUB in the form of a kernel command line, allowing the host to customize the boot process of the guest. The command line from Xen is parsed, and any variables within that start with the string `xen_grub_env_` are exposed as environment variables. The grub.cfg script can then use those environment variables as it sees fit.
The main reason for doing this is to allow implementing boot modes in Qubes OS while also using in-VM kernels. For more context on Qubes boot modes, see [1]. In order for this to work with in-VM kernels, it is necessary for dom0 to pass kernel parameters to the guest without modifying the guest's grub.cfg manually. This patch allows this to be done, by allowing dom0 to pass kernel parameters to GRUB, which then provides them to grub.cfg as an environment variable. The grub.cfg script within the VM can then append those variables to the kernel command line. The patch's code is unchanged from the last time I sent it [2], I've simply rebased it on top of the latest commit at the time of this writing (0e36779). I have not run it through the full test suite used previously, but I have ensured that both PV and PVH bootloaders build successfully and can boot an Arch Linux virtual machine on an Arch Linux host. Changes from the version 2 of the patch: * Added documentation for the future to the GRUB manual. * Fixed error checking when allocating memory. * Enhanced coding style, code efficiency, and comments based on Daniel Kiper's previous review and my own re-review. * Added an explicit null termination check on the Xen-provided kernel command line before parsing. * Fixed some memory management issues that could result in unnecessary memory consumption (one memory leak and a couple of places where an extra byte was allocated that didn't need to be). [1] https://github.com/QubesOS/qubes-linux-pvgrub2/pull/16 [2] https://lists.gnu.org/archive/html/grub-devel/2025-06/msg00011.html Aaron Rainbolt (1): kern/xen: Add Xen command line parsing docs/grub.texi | 50 +++++ grub-core/Makefile.core.def | 2 + grub-core/kern/i386/xen/pvh.c | 14 ++ grub-core/kern/main.c | 12 ++ grub-core/kern/xen/cmdline.c | 343 ++++++++++++++++++++++++++++++++++ include/grub/xen.h | 2 + 6 files changed, 423 insertions(+) create mode 100644 grub-core/kern/xen/cmdline.c -- 2.50.1
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