[systemd-devel] [PATCH 2/3] Allow $SYSTEMD_PRETEND_INITRD to override initramfs detection

[Zbigniew Jędrzejewski-Szmek]

On Mon, May 04, 2015 at 02:55:39AM +0200, Lennart Poettering wrote:
> On Sat, 02.05.15 13:16, Zbigniew Jędrzejewski-Szmek (zbyszek at in.waw.pl) wrote:
> 
> > When testing generators and other utilities, it is extremely useful
> > to be able to trigger initramfs behaviour.
> 
> Hmm, what about the following solution: instead of checking with
> access() for /etc/initrd-release and then also checking with statfs()
> on / whether the root disk is writable, maybe we should just
> immediately invoke statfs() on /etc/initrd-release and check the
> results. If the call returns ENOENT we know that the file doesn't
> exist, and if it returns useful data we can verify if it's tmpfs. 
> 
> Now, with that in place to test initrd code something like this
> suffices:
>         
>         touch /etc/initrd-release /run/initrd-release
>         mount --bind /run/initrd-release /etc/initrd-release
> 
> As that would result in a file in /etc/initrd-release that is backed
> by tmpfs....
> 
> In general I'd be very conservative when adding new APIs (which is
> basically what $SYSTEMD_PRETEND_INITRD would become), especially if we
> only need them for debugging, they are are quiet dangerous and when we
> have other options too...
Hm, this would require root privileges, and is a global setting. I'd like to
by able to do something like this:

 mkdir /tmp/x && SYSTEMD_PRETEND_INITRD=0 ./systemd-fstab-generator /tmp/{x,x,x}
 mkdir /tmp/y && SYSTEMD_PRETEND_INITRD=1 ./systemd-fstab-generator /tmp/{y,y,y}
 diff -r /tmp/{x,y}

If I have to issue some sudo stuff in between than it's probably not
worth it.

What about having a compilation time switch (like -DVALGRIND that we
already have), which would be used to conditionalize support for
SYSTEMD_PRETEND_INITRD, and potentially similar things later on? This
would make it fairly easy to build or even install systemd with
support for this, without creating a public API.

Zbyszek