Hi Eric,
On 12/17/2019 02:02 AM, Eric DeVolder wrote:
The --command-line, --append, and --reuse-cmdline options to kexec can
be used in combination to craft a kernel command line for a kernel
loaded via kexec. In addition, the kexec tool may also manipulate
further the command line, eg. elfcorehdr addition.
Thanks for proposing this change. I have some comments/queries (see below).
To aid in debugging kdump/kexec related issues, it would be helpful
for kexec to print the final constructed kernel command line argument.
For example, the following simple change (for i386/x86_64):
diff --git a/kexec/arch/i386/x86-linux-setup.c
b/kexec/arch/i386/x86-linux-setup.c
index 057ee14..6dc4adc 100644
--- a/kexec/arch/i386/x86-linux-setup.c
+++ b/kexec/arch/i386/x86-linux-setup.c
@@ -57,6 +57,8 @@ void setup_linux_bootloader_parameters_high(
char *cmdline_ptr;
unsigned long initrd_base, initrd_addr_max;
+ printf("Final kernel cmdline: '%s'\n", cmdline);
+
If we want to add this for debugging purposes, its better to have
dbgprintf() instead of printf() here. This will make sure that the debug
message is printed only when '-d' flag is specified while calling kexec
utility from command-line.
/* Say I'm a boot loader */
real_mode->loader_type = LOADER_TYPE_KEXEC << 4;
results in the following on a systemd-based system (formatted to fit
in 70 char lines):
% systemctl status -l kdump.service
● kdump.service - Crash recovery kernel arming
Loaded: loaded (/usr/lib/systemd/system/kdump.service; enabled;
vendor preset: enabled)
Active: active (exited) since Mon 2019-12-16 14:59:21 EST;
2min 53s ago
Process: 14058 ExecStop=/usr/bin/kdumpctl stop (code=exited,
status=0/SUCCESS)
Process: 14073 ExecStart=/usr/bin/kdumpctl start (code=exited,
status=0/SUCCESS)
Main PID: 14073 (code=exited, status=0/SUCCESS)
Dec 16 14:59:18 vm364 kdumpctl[14058]: Stopping kdump: [OK]
Dec 16 14:59:18 vm364 systemd[1]: Stopped Crash recovery kernel arming.
Dec 16 14:59:18 vm364 systemd[1]: Starting Crash recovery kernel arming...
Dec 16 14:59:21 vm364 kdumpctl[14073]: Final kernel cmdline: 'BOOT_IMAGE=
/vmlinuz-4.14.35-1902.7.3.1.el7uek.x86_64 ro rhgb quiet LANG=en_US.UTF-8
irqpoll nr_cpus=1 reset_devices cgroup_disable=memory mce=off numa=off
udev.children-max=2 panic=10 rootflags=nofail acpi_no_memhotplug
transparent_hugepage=never nokaslr novmcoredd disable_cpu_apicid=0
elfcorehdr=901492K'
Dec 16 14:59:21 vm364 systemd[1]: Started Crash recovery kernel arming.
Dec 16 14:59:21 vm364 kdumpctl[14073]: kexec: loaded kdump kernel
Dec 16 14:59:21 vm364 kdumpctl[14073]: Starting kdump: [OK]
and the output is also available in /var/log/messages.
Since kdumpctl is a distribution specific script (Used by Fedora/RHEL),
which invokes 'kexec' under the hood, we can discuss the features
supported by 'kexec' rather than the distribution specific scripts
(discussion regarding which are probably more suited to the Fedora kexec
list: kexec@xxxxxxxxxxxxxxxxxxxxxxx)
There might also be an opportunity to consolidate handling of the
kernel command line, as most arch targets have the --command-line,
--append, and --reuse-cmdline options, though each arch independently
codes the support for these options.
This seems like a good idea, more on the same below ...
Note: Simply printing the cmdline in scripts such as kdumpctl may not
result in the same ordering, and will omit any addition made internally
by kexec, such as the elfcorehdr.
I propose the addition of an option to kexec, --print-kcl (to mirror
--print-ckr), that would control such printing, as well as the needed
per arch conditional print statements similar to the above to print the
final constructed kernel command line.
... I am not sure I understand the above point. Looking at the latest
kexec-tools man page (see:
git://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git), I
couldn't find '--print-ckr' option:
--print-ckr-size: Print crash kernel region size, if available.
Can you please elaborate on '--print-ckr' and '--print-kcl' options more.
Thanks,
Bhupesh
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