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 Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Alexander Graf <graf@xxxxxxxxxx> Subject: initramfs: expose retained initrd as sysfs file Date: Thu, 7 Dec 2023 23:56:54 +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/20231207235654.16622-1-graf@xxxxxxxxxx Signed-off-by: Alexander Graf <graf@xxxxxxxxxx> Tested-by: Bagas Sanjaya <bagasdotme@xxxxxxxxx> 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 && initrd_start) { + 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