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

[Martin Kosek]

On 08/25/2015 08:59 PM, Alexander Bokovoy wrote:
> On Tue, 25 Aug 2015, Martin Kosek wrote:
>> On 08/25/2015 05:37 PM, Alexander Bokovoy wrote:
>>> 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.
>>
>> Sure, but given that FreeIPA upgrade is run in the posttrans phase:
>>
>> %posttrans server
>> # This must be run in posttrans so that updates from previous
>> # execution that may no longer be shipped are not applied.
>> /usr/sbin/ipa-server-upgrade --quiet >/dev/null || :
>>
>> I am now not sure how Requires(pre) or Requires(post) help here, in all
>> cases, the right selinux-policy should be there before all the posttrans
>> scripts are being run.
> I've looked at the rpm source code and here is the list of all supported
> requires/dependencies types:
> https://github.com/rpm-software-management/rpm/blob/140744377b019e0de81d76d0931c32228d2ed57e/build/rpmfc.c#L1056
>
>
> Requires(posttrans) is there so we could use this one too but it was
> added only in 4.12-alpha which means it is missing in RHEL/CentOS 7, for
> example, as they are only up to 4.11.
>> Maybe the new selinux-policy is required for certmonger itself or some other
>> event during upgrade?
> No, I don't think so. However, we cannot set Requires(posttrans), thus
> we should be using closest target before it, i.e. Requires(post).

Thank you, but I think I still did not get an answer for my question.

IIUC, the rough rpm process with regards to freeipa-server package upgrade, it 
should be in this order:

_
|
v
RPM installs some dependencies of freeipa-server
|
V
RPM installs "Requires(pre)" of freeipa-server
freeipa-server pre scriptlet runs
|
v
RPM installs freeipa-server
|
v
RPM installs "Requires(post)" of freeipa-server
freeipa-server post scriptlet runs
|
v
RPM installs some dependencies of freeipa-server
|
v
RPM executes posttrans scriptlets, including "ipa-server-upgrade".


My question is, if all the magic happens in the last step, how does adding 
(pre) or (post) Requires help, given we already have the "normal" Requires?