Hi Max, On Mon, Oct 28, 2019 at 10:58:21AM +0000, Max Tottenham via Grub-devel wrote: > Hi Folks > > I've often found myself in a position where I've needed to perform some > debugging of remote hardware that does not have a network accessible KVM > attached. To that end, being able to remotely log into a machine and > have some method of accessing GRUB2 boot time debug messages from > userspace (in my case linux), would be rather useful. It also dawned on > me that this capability might be the sort of thing that folks upstream > might be keen on. > > I have done a little thinking and have thought of two possible > approaches: > > 1. Perform some hacking of the grub environment block (load/save env) > handling to be able to write log data to either the same file in /boot, > or perhaps a separate distinct debug log file.
This can be difficult and unreliable. > 2. Export the debug log to a running kernel as another initrd image. In > other words, have GRUB2 buffer a bunch of log messages and then append > that log data as a separate initrd archive. Some early userspace program > would then be able to copy that archive to the real filesystem, or > stick it into the kernel log buffer. The logfile in the > initrd that GRUB generates could have either a configurable name based > on some setting in grub.cfg, or some well known default name (like > /grub2-debug.log) > > I initially started with 1, but I dislike the approach of having GRUB2 > write to the filesystem, it's also a little cumbersome to setup, > > Approach 2 seems like it would work (at least for linux, I've no > experience with the BSDs but presumably any OS that can load multiple > initrd's would be able to use this approach too), and has the advantage > that it doesn't have to touch any data on disk. Yeah, I think you are right. Additionally, please take a look at [1] and especially at [2]. The series is about to commit and setup_indirect part can be very useful for you. And I would like to see similar feature in the Multiboot2 protocol [3]. Additionally, I think you can take a look at ACPI ERST and UEFI variables. Both can be interesting for you and are used in Linux kernel by something called pstore (in general "grep -Ir pstore Documentation" will show you some interesting things, e.g. ramoops). Though this stuff is limited in size. Daniel [1] https://lkml.org/lkml/2019/10/24/378 [2] https://lkml.org/lkml/2019/10/24/387 [3] https://www.gnu.org/software/grub/manual/multiboot2/ _______________________________________________ Grub-devel mailing list Grub-devel@gnu.org https://lists.gnu.org/mailman/listinfo/grub-devel
