Re: [systemd-devel] Implicit unit dependency on slice might be too weak ?

2015-09-30 Thread Francis Moreau 
On Wed, Sep 30, 2015 at 11:06 PM, Lennart Poettering
 wrote:
> On Tue, 22.09.15 15:52, Lennart Poettering (lenn...@poettering.net) wrote:
>
>> On Mon, 21.09.15 16:50, Francis Moreau (francis.m...@gmail.com) wrote:
>>
>> > Hi,
>> >
>> > If a unit depends on a slice, a Wants=machine.slice is automatically
>> > added to the unit constraints.
>> >
>> > Why is "Requires=machine.slice" not prefered instead ?
>>
>> I think I agree, we should really make this a requires.
>
> This has been changed now, with 8c8da0e0cb498245c765732cf9caa081a70c560f
>

Thanks for the update.


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Re: [systemd-devel] Implicit unit dependency on slice might be too weak ?

2015-09-24 Thread Francis Moreau 
On 09/22/2015 03:52 PM, Lennart Poettering wrote:
> On Mon, 21.09.15 16:50, Francis Moreau (francis.m...@gmail.com) wrote:
> 
>> Hi,
>>
>> If a unit depends on a slice, a Wants=machine.slice is automatically
>> added to the unit constraints.
>>
>> Why is "Requires=machine.slice" not prefered instead ?
> 
> I think I agree, we should really make this a requires.
> 

One thing I noted is that even if the slice failed to start, the slice
is still created by starting the unit belonging to that slice, and the
resource controls are still correctly applied to the slice.

Is that expected that units create slice that they belong to ?

I would have expected the unit fails to start because it couldn't find
the slice.

Thanks.

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Re: [systemd-devel] Implicit unit dependency on slice might be too weak ?

2015-09-22 Thread Francis Moreau 
Hello,

On Mon, Sep 21, 2015 at 7:43 PM, David Herrmann  wrote:
> Hi
>
> On Mon, Sep 21, 2015 at 4:50 PM, Francis Moreau  
> wrote:
>> Hi,
>>
>> If a unit depends on a slice, a Wants=machine.slice is automatically
>> added to the unit constraints.
>>
>> Why is "Requires=machine.slice" not prefered instead ?
>
> Usually "Wants=" is preferred as it makes the units more fail-safe.
> Especially for slices, I cannot see why "Requires=" would be
> beneficial. If a specific unit needs this, a simple
> "Requires=foobar.slice" gets you what you want.
>

But what if the slice fails to start ?

Will the unit asking for a specific slice (which fails to start) be
moved into another slice ? It seems that whatever the final
destination used by systemd, the constraints used by the "fallback"
slice won't be correct, no ?

Thanks
-- 
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Re: [systemd-devel] Implicit unit dependency on slice might be too weak ?

2015-09-22 Thread David Herrmann 
Hi

On Tue, Sep 22, 2015 at 10:58 AM, Francis Moreau  wrote:
> Hello,
>
> On Mon, Sep 21, 2015 at 7:43 PM, David Herrmann  wrote:
>> Hi
>>
>> On Mon, Sep 21, 2015 at 4:50 PM, Francis Moreau  
>> wrote:
>>> Hi,
>>>
>>> If a unit depends on a slice, a Wants=machine.slice is automatically
>>> added to the unit constraints.
>>>
>>> Why is "Requires=machine.slice" not prefered instead ?
>>
>> Usually "Wants=" is preferred as it makes the units more fail-safe.
>> Especially for slices, I cannot see why "Requires=" would be
>> beneficial. If a specific unit needs this, a simple
>> "Requires=foobar.slice" gets you what you want.
>>
>
> But what if the slice fails to start ?
>
> Will the unit asking for a specific slice (which fails to start) be
> moved into another slice ? It seems that whatever the final
> destination used by systemd, the constraints used by the "fallback"
> slice won't be correct, no ?

Correct.

You still get a big fat error on your screen and you should fix your
setup. Again, if that's no suitable, you better use "Requires=".

Thanks
David
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Re: [systemd-devel] Implicit unit dependency on slice might be too weak ?

2015-09-22 Thread Francis Moreau 
On Tue, Sep 22, 2015 at 2:18 PM, Zbigniew Jędrzejewski-Szmek
 wrote:
> On Tue, Sep 22, 2015 at 11:52:05AM +0200, Francis Moreau wrote:
>> On Tue, Sep 22, 2015 at 11:14 AM, David Herrmann  
>> wrote:
>> > Hi
>> >
>> > On Tue, Sep 22, 2015 at 10:58 AM, Francis Moreau  
>> > wrote:
>> [...]
>> >>>
>> >>
>> >> But what if the slice fails to start ?
>> >>
>> >> Will the unit asking for a specific slice (which fails to start) be
>> >> moved into another slice ? It seems that whatever the final
>> >> destination used by systemd, the constraints used by the "fallback"
>> >> slice won't be correct, no ?
>> >
>> > Correct.
>> >
>> > You still get a big fat error on your screen and you should fix your
>> > setup. Again, if that's no suitable, you better use "Requires=".
>> >
>>
>> To put a unit in a slice, one uses by default
>>
>>Slice=myslice.slice
>>
>> and the default behaviour is to add Wants=myslice.slice to the unit.
>>
>> If the unit will always fail to start if myslice.slice fails then I
>> would say the default  behaviour should be Requires=myslice.slice.
>
> Does it actually fail? If yes, then Requires= would be better. If not,
> then Wants= should stay.
>

Well that simply means Requires= is more appropriate IMHO.

> (I tried to test this:
> - with a slice with ConditionPathExists= that is false, the
>   slice is not started and the unit is started.

The strange thing is that even if the condition is not met, the slice
is created in the cgroupfs and is used:

# cat >myservice.service

Re: [systemd-devel] Implicit unit dependency on slice might be too weak ?

2015-09-22 Thread Lennart Poettering 
On Mon, 21.09.15 16:50, Francis Moreau (francis.m...@gmail.com) wrote:

> Hi,
> 
> If a unit depends on a slice, a Wants=machine.slice is automatically
> added to the unit constraints.
> 
> Why is "Requires=machine.slice" not prefered instead ?

I think I agree, we should really make this a requires.

Lennart

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Lennart Poettering, Red Hat
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Re: [systemd-devel] Implicit unit dependency on slice might be too weak ?

2015-09-22 Thread Francis Moreau 
On Tue, Sep 22, 2015 at 11:14 AM, David Herrmann  wrote:
> Hi
>
> On Tue, Sep 22, 2015 at 10:58 AM, Francis Moreau  
> wrote:
[...]
>>>
>>
>> But what if the slice fails to start ?
>>
>> Will the unit asking for a specific slice (which fails to start) be
>> moved into another slice ? It seems that whatever the final
>> destination used by systemd, the constraints used by the "fallback"
>> slice won't be correct, no ?
>
> Correct.
>
> You still get a big fat error on your screen and you should fix your
> setup. Again, if that's no suitable, you better use "Requires=".
>

To put a unit in a slice, one uses by default

   Slice=myslice.slice

and the default behaviour is to add Wants=myslice.slice to the unit.

If the unit will always fail to start if myslice.slice fails then I
would say the default  behaviour should be Requires=myslice.slice.

I think getting an clean error to inform that the slice can't be
started at first and not trying to start the unit (which will crash
anyway) is more appropriate than getting a big fat obscure warning
because my unit will fail to start.

Thanks
-- 
Francis
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Re: [systemd-devel] Implicit unit dependency on slice might be too weak ?

2015-09-22 Thread Zbigniew Jędrzejewski-Szmek 
On Tue, Sep 22, 2015 at 11:52:05AM +0200, Francis Moreau wrote:
> On Tue, Sep 22, 2015 at 11:14 AM, David Herrmann  
> wrote:
> > Hi
> >
> > On Tue, Sep 22, 2015 at 10:58 AM, Francis Moreau  
> > wrote:
> [...]
> >>>
> >>
> >> But what if the slice fails to start ?
> >>
> >> Will the unit asking for a specific slice (which fails to start) be
> >> moved into another slice ? It seems that whatever the final
> >> destination used by systemd, the constraints used by the "fallback"
> >> slice won't be correct, no ?
> >
> > Correct.
> >
> > You still get a big fat error on your screen and you should fix your
> > setup. Again, if that's no suitable, you better use "Requires=".
> >
> 
> To put a unit in a slice, one uses by default
> 
>Slice=myslice.slice
> 
> and the default behaviour is to add Wants=myslice.slice to the unit.
> 
> If the unit will always fail to start if myslice.slice fails then I
> would say the default  behaviour should be Requires=myslice.slice.
Does it actually fail? If yes, then Requires= would be better. If not,
then Wants= should stay.

(I tried to test this:
- with a slice with ConditionPathExists= that is false, the
  slice is not started and the unit is started.
- with a slice that has [Slice] Slice=, the unit is neither started
  nor errors out:

Sep 22 08:09:27 yy systemd[1]: xxx.slice located outside its parent slice. 
Refusing.
Sep 22 08:09:27 yy systemd[1]: Cannot add dependency job for unit xxx.slice, 
ignoring: Unit xxx.slice failed to load: Invalid argument. See system logs and 
'systemctl status xxx.slice' for details.

systemd becomes unresponsive... This looks like a bug. This was
with systemd-219-23.fc22.x86_64, I'll test with something more modern
later.)

Zbyszek
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[systemd-devel] Implicit unit dependency on slice might be too weak ?

2015-09-21 Thread Francis Moreau 
Hi,

If a unit depends on a slice, a Wants=machine.slice is automatically
added to the unit constraints.

Why is "Requires=machine.slice" not prefered instead ?

Thanks.
-- 
Francis
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Re: [systemd-devel] Implicit unit dependency on slice might be too weak ?

2015-09-21 Thread David Herrmann 
Hi

On Mon, Sep 21, 2015 at 4:50 PM, Francis Moreau  wrote:
> Hi,
>
> If a unit depends on a slice, a Wants=machine.slice is automatically
> added to the unit constraints.
>
> Why is "Requires=machine.slice" not prefered instead ?

Usually "Wants=" is preferred as it makes the units more fail-safe.
Especially for slices, I cannot see why "Requires=" would be
beneficial. If a specific unit needs this, a simple
"Requires=foobar.slice" gets you what you want.

Thanks
David
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