linux-kernel - Re: [PATCH v2 0/3] init/initramfs.c: make initramfs support pivot

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Message-Id: <20210528161012.c9c8e25db29df3dbc142c62e@kernel.org>
Date:   Fri, 28 May 2021 16:10:12 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     menglong8.dong@...il.com
Cc:     mcgrof@...nel.org, josh@...htriplett.org, viro@...iv.linux.org.uk,
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Subject: Re: [PATCH v2 0/3] init/initramfs.c: make initramfs support
 pivot_root

Hi,

On Tue, 25 May 2021 22:15:21 +0800
menglong8.dong@...il.com wrote:

> From: Menglong Dong <dong.menglong@....com.cn>
> 
> As Luis Chamberlain suggested, I split the patch:
> [init/initramfs.c: make initramfs support pivot_root]
> (https://lore.kernel.org/linux-fsdevel/20210520154244.20209-1-dong.menglong@zte.com.cn/)
> into three.
> 
> The goal of the series patches is to make pivot_root() support initramfs.
> 
> In the first patch, I introduce the function ramdisk_exec_exist(), which
> is used to check the exist of 'ramdisk_execute_command' in LOOKUP_DOWN
> lookup mode.
> 
> In the second patch, I create a second mount, which is called
> 'user root', and make it become the root. Therefore, the root has a
> parent mount, and it can be umounted or pivot_root.
> 
> In the third patch, I fix rootfs_fs_type with ramfs, as it is not used
> directly any more, and it make no sense to switch it between ramfs and
> tmpfs, just fix it with ramfs to simplify the code.


This idea sounds good to me. I have tested it with MINCS container shell
script (https://github.com/mhiramat/mincs).

However, I found different issue on init_eaccess() (or symlink lookup)
with this series.

I'm using a busybox initramfs, and it makes /init as a symlink of "/sbin/init"
(absolute path)

When CONFIG_INITRAMFS_USER_ROOT=n, it booted. But CONFIG_INITRAMFS_USER_ROOT=y,
it failed to boot because it failed to find /init. If I made the /init as
a symlink of "sbin/init" (relative path), it works.

Would you have any idea?

Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>