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From:   Menglong Dong <menglong8.dong@gmail.com>
Date:   Fri, 28 May 2021 15:37:04 +0800
Message-ID: <CADxym3ZjQOmruJXZxR=LwtQRCKQiDFGXNAq+Yk_-+vLJcGchvQ@mail.gmail.com>
Subject: Re: [PATCH v2 0/3] init/initramfs.c: make initramfs support pivot_root
To:     Masami Hiramatsu <mhiramat@kernel.org>
Cc:     Luis Chamberlain <mcgrof@kernel.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Kees Cook <keescook@chromium.org>,
        Sami Tolvanen <samitolvanen@google.com>, ojeda@kernel.org,
        johan@kernel.org, Bjorn Helgaas <bhelgaas@google.com>,
        masahiroy@kernel.org, Menglong Dong <dong.menglong@zte.com.cn>,
        joe@perches.com, Jens Axboe <axboe@kernel.dk>, hare@suse.de,
        Jan Kara <jack@suse.cz>, tj@kernel.org,
        gregkh@linuxfoundation.org, song@kernel.org,
        NeilBrown <neilb@suse.de>,
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        f.fainelli@gmail.com, arnd@arndb.de,
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Hello!

On Fri, May 28, 2021 at 3:10 PM Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> Hi,
[...]
>
>
> 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?
>

Thanks for your report!

I think it's because of the path lookup on '/'. With LOOKUP_DOWN
set, the lookup for '/' of '/init' will follow the mount. However,
during the follow link of '/sbin/init', the '/' of it will not be followed,
because LOOKUP_DOWN only works one time. I'm not sure if this is an
imperfection of 'path_lookupat()'.

I'll fix it in the next series.

Thanks!
Menglong Dong