linux-kernel - Re: [PATCH v6 2/2] init/do_mounts.c: create second mount for initramfs

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Date:   Wed, 16 Jun 2021 20:57:56 -0700
From:   Menglong Dong <menglong8.dong@...il.com>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Kees Cook <keescook@...omium.org>,
        Sami Tolvanen <samitolvanen@...gle.com>, johan@...nel.org,
        ojeda@...nel.org, jeyu@...nel.org, masahiroy@...nel.org,
        joe@...ches.com, Jan Kara <jack@...e.cz>, hare@...e.de,
        Jens Axboe <axboe@...nel.dk>, tj@...nel.org,
        gregkh@...uxfoundation.org, song@...nel.org,
        NeilBrown <neilb@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Barret Rhoden <brho@...gle.com>, f.fainelli@...il.com,
        palmerdabbelt@...gle.com, wangkefeng.wang@...wei.com,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>, vbabka@...e.cz,
        Alexander Potapenko <glider@...gle.com>, pmladek@...e.com,
        johannes.berg@...el.com,
        "Eric W. Biederman" <ebiederm@...ssion.com>, jojing64@...il.com,
        terrelln@...com, geert@...ux-m68k.org,
        linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Luis Chamberlain <mcgrof@...nel.org>, arnd@...db.de,
        Chris Down <chris@...isdown.name>, mingo@...nel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Josh Triplett <josh@...htriplett.org>
Subject: Re: [PATCH v6 2/2] init/do_mounts.c: create second mount for
 initramfs

Hello,

On Mon, Jun 07, 2021 at 05:15:24AM -0700, menglong8.dong@...il.com wrote:
> On Mon, Jun 07, 2021 at 12:31:47PM +0200, Christian Brauner wrote:
> > On Sat, Jun 05, 2021 at 10:47:07PM +0800, Menglong Dong wrote:
> [...]
> > > 
> > > I think it's necessary, as I explained in the third patch. When the rootfs
> > > is a block device, ramfs is used in init_mount_tree() unconditionally,
> > > which can be seen from the enable of is_tmpfs.
> > > 
> > > That makes sense, because rootfs will not become the root if a block
> > > device is specified by 'root' in boot cmd, so it makes no sense to use
> > > tmpfs, because ramfs is more simple.
> > > 
> > > Here, I make rootfs as ramfs for the same reason: the first mount is not
> > > used as the root, so make it ramfs which is more simple.
> > 
> > Ok. If you don't mind I'd like to pull and test this before moving
> > further. (Btw, I talked about this at Plumbers before btw.)
> > What did you use for testing this? Any way you can share it?
> 

I notice that it have been ten days, and is it ok to move a little
further? (knock-knock :/)

Thanks!
Menglong Dong

> Ok, no problem definitely. I tested this function in 3 way mainly:
> 
> 1. I debug the kernel with qemu and gdb, and trace the the whole
>    process, to ensure that there is no abnormal situation.
> 2. I tested pivot_root() in initramfs and ensured that it can be
>    used normally. What's more, I also tested docker and ensured
>    container can run normally without 'DOCKER_RAMDISK=yes' set in
>    initramfs.
> 3. I tried to enable and disable CONFIG_INITRAMFS_MOUNT, and
>    ensured that the system can boot successfully from initramfs, initrd
>    and sda.
> 
> What's more, our team is going to test it comprehensively, such as
> ltp, etc.
> 
> Thanks!
> Menglong Dong                                                                                                                                                         
>