# SPDX-License-Identifier: LGPL-2.1+
#
# Copyright (c) 2021 Valve.
#
# Maintained by Guilherme G. Piccoli <gpiccoli@igalia.com>
#
#
# ###########################################################################
# ############################ SteamOS Kdump ##############################
# ###########################################################################
#
#
# This is the SteamOS Kdump/Pstore infrastructure; the goal is to collect
# data whenever a kernel crash is detected. There is a lightweight
# collection, that only grabs dmesg, and a more complete setting to grab the
# whole (compressed) vmcore. See the DETAILS section below for more info.
#
#
# ############################ HOW-TO USE IT ##############################
#
#
# 1. Install the package with pacman if not available in your image - there's
# a pre-built binary package in this gitlab; to check if it's already installed
# look the pacman installed package list. Also, be sure the systemd service was
# properly loaded by checking 'systemctl status kdump-steamos.service'.
#
# 2. Only the dmesg is collected, and by default this happens via the Pstore
# mechanism, i.e., no extra memory should be reserved and no GRUB change is
# required. If 'lsmod' shows "ramoops", then Pstore is in use.
#
# 3. The logs are stored in a ZIP file at "/home/.steamos/offload/var/kdump/";
# besides the dmesg with some extra information, the image build version,
# running kernel version and dmidecode are stored in this ZIP file as well.
# This file is named as: "steamos-SERIAL-STEAM_USER.timestamp.zip", where
# SERIAL is the machine serial (from dmidecode), STEAM_USER is the Steam
# account name (based on the last logged Steam user) and timestamp tz is UTC.
#
# 4. (IMPORTANT) Please, test the infrastructure in order to see if a dummy
# crash log is collected before using it to try debugging complex issues.
# In order to do that, login to a shell and execute, as root user:
# 'echo 1 > /proc/sys/kernel/sysrq ; echo c > /proc/sysrq-trigger'
#
# This action will trigger a dummy crash and reboot the system; check if there
# is a ZIP file with the crash logs in the directory described in (3).
#
# 5. Some tunnings are available at "/etc/default/kdump"; for example users
# can choose Kdump instead of Pstore (USE_PSTORE_RAM), and if using Kdump,
# collect the full vmcore (FULL_COREDUMP). The vmcore is not stored in the
# ZIP file, but it's saved in "/home/.steamos/offload/var/kdump/crash/".
# NOTICE that, if Kdump is used instead of Pstore, the following flags are
# needed in GRUB cmdline: "crashkernel=192M crash_kexec_post_notifiers" and
# a regular reboot is necessary.
#
#
# ############################## DETAILS ##################################
#
# CAVEATS / INSTRUCTIONS
# ###########################################################################
# (a) Currently, we don't automatically edit GRUB config; see TODO (1) below.
# This is not required if Pstore is used (which is the default).
#
# In case Kdump is used, boot-time reserved memory is required, check step (5)
# in the HOW-TO above. The memory amount was empirically determined - setting
# 144M wasn't enough and 160M is unstable, so 192M seems good enough. This
# amount might change in future kernel versions, requiring tests using the
# approach suggested in the step (4) above.
#
# (b) The kdump-steamos package requires a RW rootfs in case it's not currently
# embedded in your image. Users can make use of 'tune2fs' or 'steamos-readonly'
# in order to make the rootfs RW, since it's RO by default. Also, we assume the
# nvme partitioning scheme is default across all versions (A/B, nvme0n1p4 / p5
# are the root ones, etc) and didn't change with new updates, for example. Both
# Kdump and Pstore facilities relies in mounting partitions.
#
# (c) Due to a post-transaction hook exec'ed by libalpm (90-dracut-install.hook)
# unfortunately after installing the kdump-steamos package *all* initramfs
# images are recreated - this is not necessary, we're thinking how to prevent
# that, but for now be prepared: the installation take some (long) minutes only
# due to that ={
#
# (d) Unfortunately makedumpfile from Arch Linux is not available on official
# repos, only in AUR. But it is available on Holo, so we make use of that.
# Also, a discussion was started to get it included on official repos:
# https://lists.archlinux.org/pipermail/aur-general/2022-January/036767.html
# https://aur.archlinux.org/packages/makedumpfile/#comment-843853
#
#
# TODOs
# ###########################################################################
# (1) We'd like to be able to automatically edit GRUB and recreate its config
# file - implementation tests are ongoing.
#
# (2) The log submission mechanism is incomplete - we save the logs as a local
# ZIP file (as discussed in the HOW-TO), but they aren't submitted to a remote
# Valve server. There's an API in-place, so the implementation is starting.
#
# (3) Hopefully we can fix/prevent the unnecessary re-creation of all initramfs
# images - it happens due to our package installing files on directory
# "/usr/lib/dracut/modules.d" which triggers the unfortunate initramfs rebuild.
#
# (4) We have a "fragile" way of determining a mount point required for Kdump;
# this is something to improve maybe, in order to make the Kdump more reliable.
#
# (5) Pstore ramoops backend has some limitations that we're discussing with
# the kernel community - right now we can only collect ONE dmesg and its
# size is truncated on "record_size" bytes, not allowing a file split like
# efi-pstore; thankfully we still can collect 2MiB dmesg, but hopefully we can
# improve that upstream.
#
# (6) Add a more reliable reboot mechanism - we had seen issues in the past
# with "reboot -f", and relying in sysrq reboot as a quirk managed to be a safe
# option, so this is something to think about. Should be easy to implement.
#
# (7) Maybe a good idea would be to allow creating the minimum image for any
# specified kernel, not only for the running one (which is what we do now).
# Low-priority idea, easy to implement.
#