[RFC PATCH] rootfs: force mounting rootfs as tmpfs

Quoting Mimi Zohar (2018-02-01 13:51:52)

On Thu, 2018-02-01 at 11:09 -0600, Rob Landley wrote:

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On 02/01/2018 09:55 AM, Mimi Zohar wrote:

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On Thu, 2018-02-01 at 09:20 -0600, Rob Landley wrote:

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With your patch and specifying "root=tmpfs", dracut is complaining:

dracut: FATAL: Don't know how to handle 'root=tmpfs'
dracut: refusing to continue

[googles]... I do not understand why this package exists.

If you're switching to another root filesystem, using a tool that
wikipedia[citation needed] says has no purpose but to switch to another
root filesystem, (so let's reproduce the kernel infrastructure in
userspace while leaving it the kernel too)... why do you need initramfs
to be tmpfs? You're using it for half a second, then discarding it,
what's the point of it being tmpfs?

Unlike the kernel image which is signed by the distros, the initramfs
doesn't come signed, because it is built on the target system. ?Even
if the initramfs did come signed, it is beneficial to measure and
appraise the individual files in the initramfs.

You can still shoot yourself in the foot with tmpfs. People mount a /run
and a /tmp and then as a normal user you can go
https://twitter.com/landley/status/959103235305951233 and maybe the
default should be a little more clever there...

I'll throw it on the todo heap. :)

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Sigh. If people are ok with having rootfs just be tmpfs whenever tmpfs
is configured in, even when you're then going to overmount it with
something else like you're doing, let's just _remove_ the test. If it
can be tmpfs, have it be tmpfs.

Very much appreciated!

Not yet tested, but something like the attached? (Sorry for the
half-finished doc changes in there, I'm at work and have a 5 minute
break. I can test properly this evening if you don't get to it...)

Yes, rootfs is being mounted as tmpfs.

I don't think you can unconditionally replace ramfs with initramfs by
default. Their behavior is different in some cases (e.g. pivot_root vs
switch_root) and it can break many systems that expect ramfs by default.
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