[Freeipa-devel] [PATCH 477] spec file: Add Requires(pre) on selinux-policy

[Alexander Bokovoy]

On Tue, 25 Aug 2015, Martin Kosek wrote:
>On 08/25/2015 04:37 PM, Jan Cholasta wrote:
>> On 25.8.2015 14:50, Alexander Bokovoy wrote:
>>> On Tue, 25 Aug 2015, Jan Cholasta wrote:
>>>> On 25.8.2015 14:23, Alexander Bokovoy wrote:
>>>>> On Tue, 25 Aug 2015, Jan Cholasta wrote:
>>>>>> Hi,
>>>>>>
>>>>>> the attached patch fixes
>>>>>> <https://fedorahosted.org/freeipa/ticket/5256>.
>>>>>>
>>>>>> Honza
>>>>>>
>>>>>> --
>>>>>> Jan Cholasta
>>>>>
>>>>>> From 216be8de30747f80f490d4e91a7cca4af3e767d6 Mon Sep 17 00:00:00 2001
>>>>>> From: Jan Cholasta <jcholast at redhat.com>
>>>>>> Date: Tue, 25 Aug 2015 14:14:25 +0200
>>>>>> Subject: [PATCH] spec file: Add Requires(pre) on selinux-policy
>>>>>>
>>>>>> This prevents ipa-server-upgrade failures on SELinux AVCs because of
>>>>>> old
>>>>>> selinux-policy version.
>>>>>>
>>>>>> https://fedorahosted.org/freeipa/ticket/5256
>>>>>> ---
>>>>>> freeipa.spec.in | 1 +
>>>>>> 1 file changed, 1 insertion(+)
>>>>>>
>>>>>> diff --git a/freeipa.spec.in b/freeipa.spec.in
>>>>>> index cba91fe..fd73cda 100644
>>>>>> --- a/freeipa.spec.in
>>>>>> +++ b/freeipa.spec.in
>>>>>> @@ -139,6 +139,7 @@ Requires: systemd-units >= 38
>>>>>> Requires(pre): shadow-utils
>>>>>> Requires(pre): systemd-units
>>>>>> Requires(post): systemd-units
>>>>>> +Requires(pre): selinux-policy >= %{selinux_policy_version}
>>>>>> Requires: selinux-policy >= %{selinux_policy_version}
>>>>>> Requires(post): selinux-policy-base
>>>>>> Requires: slapi-nis >= 0.54.2-1
>>>>> If we have it in Requires(pre), we don't need it in Requires, as
>>>>> Requires(pre) is a superset of guarantees that Requires gives you.
>>>>
>>>> Martin (CCed) told me Requires(pre) does not imply Requires.
>>> See http://rpm.org/api/4.4.2.2/tsort.html (available since 2007):
>>> ----------------
>>> Since the only way out of a dependency loop is to snip the loop
>>> somewhere, rpm uses hints from Requires: dependencies to distinguish
>>> co-requisite (these are not needed to install, only to use, a package)
>>> from pre-requisite (these are guaranteed to be installed before the
>>> package that includes the dependency) relations.
>>> ----------------
>>>
>>>>>
>>>>> Requires(pre) ensures that selinux-policy of specific version is
>>>>> installed before pre scripts of freeipa-server would run, be it in the
>>>>> same transaction or in a previous one.
>>>>>
>>>>
>>>> Hmm, ipa-server-upgrade is run in posttrans. Should the Requires(pre)
>>>> be changed to Required(posttrans)?
>>> I don't think there is posttrans target. Perhaps, we can just make sure
>>> Requires(post) is enough.
>>
>> OK, let's try that. Updated patch attached.
>>
>
>Will this really make a difference? I thought the problem is caused by
>selinux-policy being installed after freeipa-server package upgrade. We already
>have Requires on selinux-policy, so I am not sure what is actually changed by
>this patch.
The change is that with Requires(pre) or Requires(post) we are
guaranteed that selinux-policy is installed and available before our pre
or post scriptlets are run. With Requires only we are not guaranteed to
be installed after selinux-policy, only that it would be available as
part of the same transaction we are installed in.

We don't really need to have Requires(pre) because we don't rely on
selinux-policy being available in pre scriptlet. Forcing Requires(pre)
doesn't help anyone else (rpm/yum/dnf need to solve dependency loops and
we are only complicating with Requires(pre) if we don't actually need
it). Thus, choosing Require(post) is more correct from distribution
point of view.
-- 
/ Alexander Bokovoy