[Buildroot] [PATCH 2/3] Rework of the init system

[Maxime Ripard]

Hi,

On 06/01/2012 08:13, Arnout Vandecappelle wrote:
> On Monday 02 January 2012 10:52:13 Maxime Ripard wrote:
>> On 20/12/2011 09:03, Arnout Vandecappelle wrote:
>>> On Wednesday 23 November 2011 12:30:10 Maxime Ripard wrote:
> [snip]
>>>> diff --git a/package/busybox/busybox.mk b/package/busybox/busybox.mk
>>>> index 9e91136..73c4969 100644
>>>> --- a/package/busybox/busybox.mk
>>>> +++ b/package/busybox/busybox.mk
>>>> @@ -129,6 +129,16 @@ define BUSYBOX_DISABLE_MMU_APPLETS
>>>>  endef
>>>>  endif
>>>>  
>>>> +ifeq ($(BR2_INIT_BUSYBOX),y)
>>>> +define BUSYBOX_SET_INIT
>>>> +	$(call KCONFIG_ENABLE_OPT,CONFIG_INIT,$(BUSYBOX_BUILD_CONFIG))
>>>> +endef
>>>> +else
>>>> +define BUSYBOX_SET_INIT
>>>> +	$(call KCONFIG_DISABLE_OPT,CONFIG_INIT,$(BUSYBOX_BUILD_CONFIG))
>>>> +endef
>>>> +endif
>>>> +
>>>  I'm not sure if I'd want to have the disable there if BR2_INIT_BUSYBOX
>>> is not selected.  There's nothing against a parallel install of
>>> systemd and busybox-init, selectable by 'init=...' on the kernel
>>> command line.  (Well, except that systemd's symlinks destroy busybox init.)
>>
>> Well mutually exclusive init systems is the more obvious solution.
>> Having an sysv init and systemd should be ok at the same time should be
>> ok indeed, at least from a filesystem and boot point of view, but it
>> will probably be more problematic for the init scripts.
> 
>  Just to be clear: I agree that we should only support mutually exclusive
> init systems, but NOT mutually exclusive init packages.  In other words,
> BR2_INIT_{BUSYBOX,SYSV,SYSTEMD} should be mutually exclusive.  However, 
> IMO that doesn't mean that the unused binaries should be forcibly removed 
> from the system.  In the current situation, it is also possible to compile 
> the init applet of busybox and at the same time install the sysvinit package
> (where the sysvinit package will remove busybox's symlink).
> 
>  The main reason to allow both packages in parallel is that making them
> mutually exclusive adds complexity, while it is difficult to be sure that
> it really enforces mutual exclusivity in all situations.  There are many
> cases where two packages supply the same functionality (especially with
> busybox), and buildroot does little (and should do little) to enforce
> that only one of them is used.
> 
>  Also enforcing it gives little benefit.  You would normally not select
> any init package explicitly, you'd only select a BR2_INIT_ option.  If
> you do select an init package explicitly after all, there may be a good
> reason for it.  (Of course, this does mean that init should be removed
> from the default busybox configs.)
> 
>  The second reason is that it could make sense to have both (especially
> during development).  So why spend extra effort to disable something
> that could be useful?

Ok, it makes sense

> 
>> From what I understood of it, if init scripts are presents, systemd will
>> check the name to see if it has a unit for this, and will prefer the
>> unit if it has one. But I'm not sure how it will behave with our way of
>> naming the init scripts.
> 
>  That's something else: buildroot should install only one set of init 
> scripts, either sysv or systemd.  If you really want both, you'll have
> to put it in the skeleton.

I agree, but you seem to say otherwise in your other mail from today. To
me, there is no need for us to add a fallback to sysv scripts. You will
be in one of the three cases :
  - You use sysvinit or busybox and the package has a sysv script: Great
  - You use systemd and the package has no systemd unit file: Send a patch
  - You use systemd and the package has a systemd unit file: Great

As simple as that.

>>>> diff --git a/package/systemd/Config.in b/package/systemd/Config.in
>>>> index 09cedb9..33d5ccf 100644
>>>> --- a/package/systemd/Config.in
>>>> +++ b/package/systemd/Config.in
>>>> @@ -1,5 +1,6 @@
>>>>  config BR2_PACKAGE_SYSTEMD
>>>>  	bool "systemd"
>>>> +	depends on BR2_INIT_SYSTEMD
>>>  Again, there is no reason why you can't have sysvinit and systemd in
>>> parallel (except for the symlinks).  Also, if you really want them to
>>> be mutually exclusive, I'd prefer the more explicit
>>> 	depends on !BR2_PACKAGE_SYSVINIT
>>
>> Hmmm, you mean BR2_INIT_SYSV ?
> 
>  Well, actually: if you want them to be mutually exclusive, the systemd
> package (and the sysvinit package) have no place in the menuconfig, so
> instead it should be:
> 
> config BR2_PACKAGE_SYSTEMD
> 	depends on BR2_INIT_SYSTEMD
> 
> This will make sure it gets selected if and only if BR2_INIT_SYSTEMD is
> selected, and will hide it from the menuconfig.

Right.

Maxime
-- 
Maxime Ripard, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com