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Message-ID: <20251021-bannmeile-arkaden-ae2ea9264b85@brauner> Date: Tue, 21 Oct 2025 15:05:35 +0200 From: Christian Brauner <brauner@...nel.org> To: Askar Safin <safinaskar@...il.com>, Christoph Hellwig <hch@...radead.org> Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, Linus Torvalds <torvalds@...ux-foundation.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Al Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>, Andy Shevchenko <andy.shevchenko@...il.com>, Aleksa Sarai <cyphar@...har.com>, Thomas Weißschuh <thomas.weissschuh@...utronix.de>, Julian Stecklina <julian.stecklina@...erus-technology.de>, Gao Xiang <hsiangkao@...ux.alibaba.com>, Art Nikpal <email2tema@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, Alexander Graf <graf@...zon.com>, Rob Landley <rob@...dley.net>, Lennart Poettering <mzxreary@...inter.de>, linux-arch@...r.kernel.org, linux-block@...r.kernel.org, initramfs@...r.kernel.org, linux-api@...r.kernel.org, linux-doc@...r.kernel.org, Michal Simek <monstr@...str.eu>, Luis Chamberlain <mcgrof@...nel.org>, Kees Cook <kees@...nel.org>, Thorsten Blum <thorsten.blum@...ux.dev>, Heiko Carstens <hca@...ux.ibm.com>, Arnd Bergmann <arnd@...db.de>, Dave Young <dyoung@...hat.com>, Christophe Leroy <christophe.leroy@...roup.eu>, Krzysztof Kozlowski <krzk@...nel.org>, Borislav Petkov <bp@...en8.de>, Jessica Clarke <jrtc27@...c27.com>, Nicolas Schichan <nschichan@...ebox.fr>, David Disseldorp <ddiss@...e.de>, patches@...ts.linux.dev Subject: Re: [PATCH v3 0/3] initrd: remove half of classic initrd support On Fri, Oct 17, 2025 at 06:09:53AM +0000, Askar Safin wrote: > Intro > ==== > This patchset removes half of classic initrd (initial RAM disk) support, > i. e. linuxrc code path, which was deprecated in 2020. > Initramfs still stays, RAM disk itself (brd) still stays. > And other half of initrd stays, too. > init/do_mounts* are listed in VFS entry in > MAINTAINERS, so I think this patchset should go through VFS tree. > I tested the patchset on 8 (!!!) archs in Qemu (see details below). > If you still use initrd, see below for workaround. > > In 2020 deprecation notice was put to linuxrc initrd code path. > In v1 I tried to remove initrd > fully, but Nicolas Schichan reported that he still uses > other code path (root=/dev/ram0 one) on million devices [4]. > root=/dev/ram0 code path did not contain deprecation notice. Without Acks or buy-in from other maintainers this is not a change we can just do given that a few people already piped up and expressed reservations that this would be doable for them. @Christoph, you marked this as deprecated years ago. What's your take on this? > > So, in this version of patchset I remove deprecated code path, > i. e. linuxrc one, while keeping other, i. e. root=/dev/ram0 one. > > Also I put deprecation notice to remaining code path, i. e. to > root=/dev/ram0 one. I plan to send patches for full removal > of initrd after one year, i. e. in September 2026 (of course, > initramfs will still work). > > Also, I tried to make this patchset small to make sure it > can be reverted easily. I plan to send cleanups later. > > Details > ==== > Other user-visible changes: > > - Removed kernel command line parameters "load_ramdisk" and > "prompt_ramdisk", which did nothing and were deprecated > - Removed /proc/sys/kernel/real-root-dev . It was used > for initrd only > - Command line parameters "noinitrd" and "ramdisk_start=" are deprecated > > This patchset is based on v6.18-rc1. > > Testing > ==== > I tested my patchset on many architectures in Qemu using my Rust > program, heavily based on mkroot [1]. > > I used the following cross-compilers: > > aarch64-linux-musleabi > armv4l-linux-musleabihf > armv5l-linux-musleabihf > armv7l-linux-musleabihf > i486-linux-musl > i686-linux-musl > mips-linux-musl > mips64-linux-musl > mipsel-linux-musl > powerpc-linux-musl > powerpc64-linux-musl > powerpc64le-linux-musl > riscv32-linux-musl > riscv64-linux-musl > s390x-linux-musl > sh4-linux-musl > sh4eb-linux-musl > x86_64-linux-musl > > taken from this directory [2]. > > So, as you can see, there are 18 triplets, which correspond to 8 subdirs in arch/. > > For every triplet I tested that: > - Initramfs still works (both builtin and external) > - Direct boot from disk still works > - Remaining initrd code path (root=/dev/ram0) still works > > Workaround > ==== > If "retain_initrd" is passed to kernel, then initramfs/initrd, > passed by bootloader, is retained and becomes available after boot > as read-only magic file /sys/firmware/initrd [3]. > > No copies are involved. I. e. /sys/firmware/initrd is simply > a reference to original blob passed by bootloader. > > This works even if initrd/initramfs is not recognized by kernel > in any way, i. e. even if it is not valid cpio archive, nor > a fs image supported by classic initrd. > > This works both with my patchset and without it. > > This means that you can emulate classic initrd so: > link builtin initramfs to kernel; in /init in this initramfs > copy /sys/firmware/initrd to some file in / and loop-mount it. > > This is even better than classic initrd, because: > - You can use fs not supported by classic initrd, for example erofs > - One copy is involved (from /sys/firmware/initrd to some file in /) > as opposed to two when using classic initrd > > Still, I don't recommend using this workaround, because > I want everyone to migrate to proper modern initramfs. > But still you can use this workaround if you want. > > Also: it is not possible to directly loop-mount > /sys/firmware/initrd . Theoretically kernel can be changed > to allow this (and/or to make it writable), but I think nobody needs this. > And I don't want to implement this. > > On Qemu's -initrd and GRUB's initrd > ==== > Don't panic, this patchset doesn't remove initramfs > (which is used by nearly all Linux distros). And I don't > have plans to remove it. > > Qemu's -initrd option and GRUB's initrd command refer > to initrd bootloader mechanism, which is used to > load both initrd and (external) initramfs. > > So, if you use Qemu's -initrd or GRUB's initrd, > then you likely use them to pass initramfs, and thus > you are safe. > > v1: https://lore.kernel.org/lkml/20250913003842.41944-1-safinaskar@gmail.com/ > > v1 -> v2 changes: > - A lot. I removed most patches, see cover letter for details > > v2: https://lore.kernel.org/lkml/20251010094047.3111495-1-safinaskar@gmail.com/ > > v2 -> v3 changes: > - Commit messages > - Expanded docs for "noinitrd" > - Added link to /sys/firmware/initrd workaround to pr_warn > > [1] https://github.com/landley/toybox/tree/master/mkroot > [2] https://landley.net/toybox/downloads/binaries/toolchains/latest > [3] https://lore.kernel.org/all/20231207235654.16622-1-graf@amazon.com/ > [4] https://lore.kernel.org/lkml/20250918152830.438554-1-nschichan@freebox.fr/ > > Askar Safin (3): > init: remove deprecated "load_ramdisk" and "prompt_ramdisk" command > line parameters > initrd: remove deprecated code path (linuxrc) > init: remove /proc/sys/kernel/real-root-dev > > .../admin-guide/kernel-parameters.txt | 12 +- > Documentation/admin-guide/sysctl/kernel.rst | 6 - > arch/arm/configs/neponset_defconfig | 2 +- > fs/init.c | 14 --- > include/linux/init_syscalls.h | 1 - > include/linux/initrd.h | 2 - > include/uapi/linux/sysctl.h | 1 - > init/do_mounts.c | 11 +- > init/do_mounts.h | 18 +-- > init/do_mounts_initrd.c | 107 ++---------------- > init/do_mounts_rd.c | 24 +--- > 11 files changed, 23 insertions(+), 175 deletions(-) > > > base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787 > -- > 2.47.3 >
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