linux-kernel - RE: [PATCH v4 0/3] initramfs: add support for xattrs in the initial ram disk

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Date:   Tue, 19 Jul 2022 12:26:02 +0000
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     Rob Landley <rob@...dley.net>, Jim Baxter <jim_baxter@...tor.com>,
        "Eugeniu Rosca" <erosca@...adit-jv.com>
CC:     "hpa@...or.com" <hpa@...or.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "initramfs@...r.kernel.org" <initramfs@...r.kernel.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "bug-cpio@....org" <bug-cpio@....org>,
        "zohar@...ux.vnet.ibm.com" <zohar@...ux.vnet.ibm.com>,
        Silviu Vlasceanu <Silviu.Vlasceanu@...wei.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...wei.com>,
        "takondra@...co.com" <takondra@...co.com>,
        "kamensky@...co.com" <kamensky@...co.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "james.w.mcmechan@...il.com" <james.w.mcmechan@...il.com>,
        "linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>,
        Dirk Behme <dirk.behme@...bosch.com>,
        Eugeniu Rosca <roscaeugeniu@...il.com>
Subject: RE: [PATCH v4 0/3] initramfs: add support for xattrs in the initial
 ram disk

> From: Rob Landley [mailto:rob@...dley.net]
> Sent: Tuesday, July 19, 2022 1:51 PM
> On 7/19/22 01:55, Roberto Sassu wrote:
> >> Thank you, I have tested that patch but the problem remained. Here is my
> >> command line, I wonder if there is something wrong.
> >>
> >> Kernel command line: rw rootfstype=initramtmpfs root=/dev/ram0
> >> initrd=0x500000000 rootwait
> >
> > It is just initramtmpfs, without rootfstype=.
> 
> Whoever wrote that patch really doesn't understand how this stuff works. I can
> tell from the name.

Hi Rob

surely, I should have been more careful in choosing the name of
the option.

> Technically, initramfs is the loader, I.E. "init ramfs". The filesystem instance
> is called "rootfs" (hence the name in /proc/mounts when the insane special case
> the kernel added doesn't hide information from people, making all this harder to
> understand for no obvious reason).

Ok, thanks for the explanation.

> ramfs and tmpfs are two different filesystems that COULD be used to implement
> rootfs. (Last I checked they were the only ram backed filesystems in Linux.)

Yes, that part I got it.

> If a system administrator says they're going to install your server's root
> partition using the "reiserxfs" filesystem, I would not be reassured.

Definitely.

[...]

> P.P.S. If you want to run a command other than /init out of initramfs or initrd,
> use the rdinit=/run/this option. Note the root= overmount mechanism is
> completely different code and uses the init=/run/this argument instead, which
> means nothing to initramfs. Again, specifying root= says we are NOT staying in
> initramfs.

Sorry, it was some time ago. I have to go back and see why we needed
a separate option. Maybe omitting root= was impacting on mounting
the real root filesystem. Will get that information.

Intuitively, given that root= is consumed for example by dracut, it seems
a safer choice to have an option to explicitly choose the desired filesystem.

Roberto