The patch titled
Subject: initramfs: expose retained initrd as sysfs file
has been added to the -mm mm-nonmm-unstable branch. Its filename is
initramfs-expose-retained-initrd-as-sysfs-file.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/initramfs-expose-retained-initrd-as-sysfs-file.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Alexander Graf <graf@xxxxxxxxxx>
Subject: initramfs: expose retained initrd as sysfs file
Date: Wed, 6 Dec 2023 21:33:23 +0000
When the kernel command line option "retain_initrd" is set, we do not free
the initrd memory. However, we also don't expose it to anyone for
consumption. That leaves us in a weird situation where the only user of
this feature is ppc64 and arm64 specific kexec tooling.
To make it more generally useful, this patch adds a kobject to the
firmware object that contains the initrd context when "retain_initrd" is
set. That way, we can access the initrd any time after boot from user
space and for example hand it into kexec as --initrd parameter if we want
to reboot the same initrd. Or inspect it directly locally.
With this patch applied, there is a new /sys/firmware/initrd file when the
kernel was booted with an initrd and "retain_initrd" command line option
is set.
Link: https://lkml.kernel.org/r/20231206213323.78233-1-graf@xxxxxxxxxx
Signed-off-by: Alexander Graf <graf@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: James Gowans <jgowans@xxxxxxxxxx>
Cc: Jan H. Schönherr <jschoenh@xxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/ABI/testing/sysfs-firmware-initrd | 8 ++++++
Documentation/admin-guide/kernel-parameters.txt | 5 ++-
init/initramfs.c | 18 +++++++++++++-
3 files changed, 28 insertions(+), 3 deletions(-)
--- /dev/null
+++ a/Documentation/ABI/testing/sysfs-firmware-initrd
@@ -0,0 +1,8 @@
+What: /sys/firmware/initrd
+Date: December 2023
+Contact: Alexander Graf <graf@xxxxxxxxxx>
+Description:
+ When the kernel was booted with an initrd and the
+ "retain_initrd" option is set on the kernel command
+ line, /sys/firmware/initrd contains the contents of the
+ initrd that the kernel was booted with.
--- a/Documentation/admin-guide/kernel-parameters.txt~initramfs-expose-retained-initrd-as-sysfs-file
+++ a/Documentation/admin-guide/kernel-parameters.txt
@@ -2438,7 +2438,7 @@
between unregistering the boot console and initializing
the real console.
- keepinitrd [HW,ARM]
+ keepinitrd [HW,ARM] See retain_initrd.
kernelcore= [KNL,X86,IA-64,PPC]
Format: nn[KMGTPE] | nn% | "mirror"
@@ -5580,7 +5580,8 @@
Useful for devices that are detected asynchronously
(e.g. USB and MMC devices).
- retain_initrd [RAM] Keep initrd memory after extraction
+ retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will
+ be accessible via /sys/firmware/initrd.
retbleed= [X86] Control mitigation of RETBleed (Arbitrary
Speculative Code Execution with Return Instructions)
--- a/init/initramfs.c~initramfs-expose-retained-initrd-as-sysfs-file
+++ a/init/initramfs.c
@@ -574,6 +574,16 @@ extern unsigned long __initramfs_size;
#include <linux/initrd.h>
#include <linux/kexec.h>
+static ssize_t raw_read(struct file *file, struct kobject *kobj,
+ struct bin_attribute *attr, char *buf,
+ loff_t pos, size_t count)
+{
+ memcpy(buf, attr->private + pos, count);
+ return count;
+}
+
+static BIN_ATTR(initrd, 0440, raw_read, NULL, 0);
+
void __init reserve_initrd_mem(void)
{
phys_addr_t start;
@@ -715,8 +725,14 @@ done:
* If the initrd region is overlapped with crashkernel reserved region,
* free only memory that is not part of crashkernel region.
*/
- if (!do_retain_initrd && initrd_start && !kexec_free_initrd())
+ if (!do_retain_initrd && initrd_start && !kexec_free_initrd()) {
free_initrd_mem(initrd_start, initrd_end);
+ } else if (do_retain_initrd) {
+ bin_attr_initrd.size = initrd_end - initrd_start;
+ bin_attr_initrd.private = (void *)initrd_start;
+ if (sysfs_create_bin_file(firmware_kobj, &bin_attr_initrd))
+ pr_err("Failed to create initrd sysfs file");
+ }
initrd_start = 0;
initrd_end = 0;
_
Patches currently in -mm which might be from graf@xxxxxxxxxx are
initramfs-expose-retained-initrd-as-sysfs-file.patch
