[Buildroot] [PATCH] dhcp: add systemd service file

[Yann E. MORIN <yann.morin.1998@free.fr>]

Eric, All,

On 2014-09-22 12:52 +0200, Eric Le Bihan spake thusly:
> On Sun, Sep 21, 2014 at 10:44:45PM +0200, Yann E. MORIN wrote:
> > On 2014-09-15 23:04 +0200, Eric Le Bihan spake thusly:
> > > Add a systemd service file to start dhcpd.
[--SNIP--]
> > > +	echo "d /var/lib/dhcp 0755 - - - -" > \
> > > +		$(TARGET_DIR)/usr/lib/tmpfiles.d/dhcpd.conf
> > > +	echo "f /var/lib/dhcp/dhcpd.leases - - - - -" >> \
> > > +		$(TARGET_DIR)/usr/lib/tmpfiles.d/dhcpd.conf
> >
> > I'm not sure to understand those two. Are they needed on the target?
> >
> > They suspiciously look like our 'makedev' syntax. Does systemd recognise
> > this too?
> 
> Among the zillion of tools provided by systemd, there is 'systemd-tmpfiles'
> [1]. This program creates, deletes, and cleans up volatile and temporary
> files and directories based on configuration files stored in
> /usr/lib/tmpfiles.d and /etc/tmpfiles.d.
> 
> It is true that these files follow a syntax similar to makedev [2]. But unlike
> 'makedev' which sets the proper access rights for / entries at build time,
> 'systemd-tmpfiles' creates the files at runtime if they are missing.
> 
> In the current default skeleton used by Buildroot, parts of /var are
> tmpfs-based and thus get cleaned at each reboot. 'systemd-tmpfiles' can
> recreate them.
> 
> For some reasons, when using systemd, dhcpd complains at start-up about
> /var/lib/dhcp/dhcpd.leases not being accessible. So the Makefile installs a
> file named /usr/lib/tmpfiles.d/dhcp.conf, which contains "instructions" for
> creating the missing file with the proper access rights.

Thanks for the thorough explanations!

> I know that a package named 'foo' can add system users via FOO_USERS, thanks
> to 'mkusers'. Can the same be done with 'makedev'?

Yes, it is possible, see:
    http://nightly.buildroot.org/#_infrastructure_for_packages_with_specific_build_systems
and:
    http://nightly.buildroot.org/#makedev-syntax

You'd need something like:

    define LIBFOO_PERMISSIONS
        /var/lib/dhcp d 0755 0 0 - - - - -
        /var/lib/dhcp/dhcpd.leases f 0600 0 0 - - - - -
    endef

> This would allow a package
> to create files with the proper owner and access rights without having to
> provide additional files.

Problem is /var/lib/dhcp/dhcpd.leases should be on a RW filesystem, and
the only one Buildroot gurantees to be RW is /tmp (which is a tmpfs).

But /var/lib does not point to a subdir in /tmp so whether we use
systemd's feature to create missing files, or the makedev above, we'd
still need to make /var/lib/dhcp a symling to somewhere in /tmp.

Regards,
Yann E. MORIN.

> Side note: since version 215, systemd provides systemd-sysusers, which creates
> system users and groups in /etc/passwd and /etc/group based on the
> configuration files in /usr/lib/sysusers.d/. It is said to be useful for
> systems where /etc can be "reset" to a default version. I still haven't found
> a useful use case for it in an embedded system, though.
> 
> [1] http://www.freedesktop.org/software/systemd/man/systemd-tmpfiles.html
> [2] http://www.freedesktop.org/software/systemd/man/tmpfiles.d.html
> 
> Best regards,
> ELB

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