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

From: Roberto Sassu <roberto.sassu@huawei.com>
To: Rob Landley <rob@landley.net>, Jim Baxter <jim_baxter@mentor.com>,
	"Eugeniu Rosca" <erosca@de.adit-jv.com>
Cc: "hpa@zytor.com" <hpa@zytor.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Arvind Sankar <nivedita@alum.mit.edu>,
	Mimi Zohar <zohar@linux.ibm.com>,
	"viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>,
	"linux-security-module@vger.kernel.org" 
	<linux-security-module@vger.kernel.org>,
	"linux-integrity@vger.kernel.org"
	<linux-integrity@vger.kernel.org>,
	"initramfs@vger.kernel.org" <initramfs@vger.kernel.org>,
	"linux-api@vger.kernel.org" <linux-api@vger.kernel.org>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"bug-cpio@gnu.org" <bug-cpio@gnu.org>,
	"zohar@linux.vnet.ibm.com" <zohar@linux.vnet.ibm.com>,
	Silviu Vlasceanu <Silviu.Vlasceanu@huawei.com>,
	Dmitry Kasatkin <dmitry.kasatkin@huawei.com>,
	"takondra@cisco.com" <takondra@cisco.com>,
	"kamensky@cisco.com" <kamensky@cisco.com>,
	"arnd@arndb.de" <arnd@arndb.de>,
	"james.w.mcmechan@gmail.com" <james.w.mcmechan@gmail.com>,
	"linux-kbuild@vger.kernel.org" <linux-kbuild@vger.kernel.org>,
	Dirk Behme <dirk.behme@de.bosch.com>,
	Eugeniu Rosca <roscaeugeniu@gmail.com>
Subject: RE: [PATCH v4 0/3] initramfs: add support for xattrs in the initial ram disk
Date: Tue, 19 Jul 2022 12:26:02 +0000	[thread overview]
Message-ID: <5b8b0bcac01b477eaa777ceb8c109f58@huawei.com> (raw)
In-Reply-To: <dc86769f-0ac6-d9f3-c003-54d3793ccfec@landley.net>

> From: Rob Landley [mailto:rob@landley.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