On Thu, Dec 07, 2023 at 11:56:54PM +0000, Alexander Graf wrote: > 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. > > Signed-off-by: Alexander Graf <graf@xxxxxxxxxx> > Tested-by: Bagas Sanjaya <bagasdotme@xxxxxxxxx> > > --- > > v1 -> v2: > > - Reword commit message to explain the new file path > - Add a Documentation/ABI/testing/sysfs-firmware-initrd file > > v2 -> v3: > > - Only expose file when initrd is present (James Gowans) > --- > .../ABI/testing/sysfs-firmware-initrd | 8 ++++++++ > .../admin-guide/kernel-parameters.txt | 5 +++-- > init/initramfs.c | 18 +++++++++++++++++- > 3 files changed, 28 insertions(+), 3 deletions(-) > create mode 100644 Documentation/ABI/testing/sysfs-firmware-initrd > > diff --git a/Documentation/ABI/testing/sysfs-firmware-initrd b/Documentation/ABI/testing/sysfs-firmware-initrd > new file mode 100644 > index 000000000000..20bf7cf77a19 > --- /dev/null > +++ b/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. > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index 65731b060e3f..51575cd31741 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/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) You may want to adjust documentation to address my testing [1]. In summary, only the first initrd blob that was passed to the kernel will be exposed in /sys/firmware/initrd. Thanks. [1]: https://lore.kernel.org/linux-doc/2a86a7f2-bbf3-43fb-82b9-40d3397d5578@xxxxxxxxxx/ -- An old man doll... just what I always wanted! - Clara
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