linux-kernel - Re: [PATCH] initrd: support erofs as initrd

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Message-ID: <198facfefe8.11982931078232.326054837204882979@zohomail.com>
Date: Sat, 30 Aug 2025 15:49:48 +0400
From: Askar Safin <safinaskar@...omail.com>
To: "Gao Xiang" <hsiangkao@...ux.alibaba.com>
Cc: "Byron Stanoszek" <gandalf@...ds.org>, "Christoph Hellwig" <hch@....de>,
	"gregkh" <gregkh@...uxfoundation.org>,
	"julian.stecklina" <julian.stecklina@...erus-technology.de>,
	"linux-fsdevel" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel" <linux-kernel@...r.kernel.org>,
	"rafael" <rafael@...nel.org>,
	"torvalds" <torvalds@...ux-foundation.org>,
	"viro" <viro@...iv.linux.org.uk>,
	"Thomas Weißschuh" <thomas.weissschuh@...utronix.de>,
	"Christian Brauner" <brauner@...nel.org>,
	"systemd-devel" <systemd-devel@...ts.freedesktop.org>,
	"Lennart Poettering" <mzxreary@...inter.de>
Subject: Re: [PATCH] initrd: support erofs as initrd

 ---- On Thu, 28 Aug 2025 21:14:34 +0400  Gao Xiang <hsiangkao@...ux.alibaba.com> wrote --- 
 > Which part of the running system check the cpio signature.

You mean who checks cpio signature at boot?
Ideally, bootloader should do this.

For example, as well as I understand, UKI's EFI stub checks
initramfs signature. (See
https://github.com/systemd/systemd/blob/main/docs/ROOTFS_DISCOVERY.md
).

It seems that this document (ROOTFS_DISCOVERY) covers
zillions of use cases, so I hope you will find something for you.

I also added to CC Poettering and systemd, hopefully they have some
ideas.

 > Why users need to extract the whole cpio to tmpfs just for some data
 > part in the erofs? even some data is never used?

Initramfs should be small. Time for extracting should not matter.
If initramfs is too big, and time becomes issue, you are doing it
wrong.

Point of initramfs is to be transition stage and then get to real root.
Initramfs should not be feature-rich and should not be big.

 > Personally I just don't understand why cpio stands out considering it
 > even the format itself doesn't support xattrs and more.

As I said above, initramfs should not be feature-rich.

(But xattrs can be added to it, if needed.)

-- 
Askar Safin
https://types.pl/@safinaskar