GNU bug report logs - #77109
[feature] [shepherd] Accept multiple services for actions

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Maxim Cournoyer <maxim.cournoyer <at> gmail.com>
To: bug-guix <bug-guix <at> gnu.org>
Subject: [feature] [shepherd] Accept multiple services for actions
Date: Wed, 19 Mar 2025 15:02:38 +0900

Hi,

Coming from a world where 'guix install package1 package2 ...' is a thing, I
sometimes would like to be able to do:

--8<---------------cut here---------------start------------->8---
herd restart service1 service2 ...
--8<---------------cut here---------------end--------------->8---

Which Shepherd gladly accepts but disregarding service2 ...

Would it be a good idea to teach the Shepherd how to do this?

-- 
Thanks,
Maxim

Message #8 received at 77109 <at> debbugs.gnu.org (full text, mbox):

From: Tomas Volf <~@wolfsden.cz>
To: Maxim Cournoyer <maxim.cournoyer <at> gmail.com>
Cc: 77109 <at> debbugs.gnu.org
Subject: Re: bug#77109: [feature] [shepherd] Accept multiple services for
 actions
Date: Wed, 19 Mar 2025 14:00:12 +0100

[Message part 1 (text/plain, inline)]

Maxim Cournoyer <maxim.cournoyer <at> gmail.com> writes:

> Hi,
>
> Coming from a world where 'guix install package1 package2 ...' is a thing, I
> sometimes would like to be able to do:
>
> herd restart service1 service2 ...
>
> Which Shepherd gladly accepts but disregarding service2 ...
>
> Would it be a good idea to teach the Shepherd how to do this?

I guess it could be special-cased for start, stop, restart, since these
three do not take (by default) any arguments (I *think* you can make
`start' procedure taking arguments?  I have never tried.).  But for
general case, the `service2' is passed as an argument to the action
`restart' of service `service1'.

I am not sure having different semantics for restart and any other
action is a good idea though.

But what I think would be a good idea is for start, stop, restart to
signal an error when additional unexpected arguments are provided.

Tomas

-- 
There are only two hard things in Computer Science:
cache invalidation, naming things and off-by-one errors.

[signature.asc (application/pgp-signature, inline)]

Message #11 received at 77109 <at> debbugs.gnu.org (full text, mbox):

From: Ludovic Courtès <ludo <at> gnu.org>
To: Tomas Volf <~@wolfsden.cz>
Cc: 77109 <at> debbugs.gnu.org, Maxim Cournoyer <maxim.cournoyer <at> gmail.com>
Subject: Re: bug#77109: [feature] [shepherd] Accept multiple services for
 actions
Date: Wed, 19 Mar 2025 19:57:30 +0100

Hi,

Tomas Volf <~@wolfsden.cz> skribis:

> I guess it could be special-cased for start, stop, restart, since these
> three do not take (by default) any arguments (I *think* you can make
> `start' procedure taking arguments?  I have never tried.).  But for
> general case, the `service2' is passed as an argument to the action
> `restart' of service `service1'.

I think we could special-case that on the client side (in ‘herd’) with
something like:

  herd restart --batch s1 s2 s3

which would restart those services one after the other.

WDYT?

Ludo’.

Message #14 received at 77109 <at> debbugs.gnu.org (full text, mbox):

From: Tomas Volf <~@wolfsden.cz>
To: Ludovic Courtès <ludo <at> gnu.org>
Cc: 77109 <at> debbugs.gnu.org, Maxim Cournoyer <maxim.cournoyer <at> gmail.com>
Subject: Re: bug#77109: [feature] [shepherd] Accept multiple services for
 actions
Date: Wed, 19 Mar 2025 20:47:25 +0100

[Message part 1 (text/plain, inline)]

Ludovic Courtès <ludo <at> gnu.org> writes:

> Hi,
>
> Tomas Volf <~@wolfsden.cz> skribis:
>
>> I guess it could be special-cased for start, stop, restart, since these
>> three do not take (by default) any arguments (I *think* you can make
>> `start' procedure taking arguments?  I have never tried.).  But for
>> general case, the `service2' is passed as an argument to the action
>> `restart' of service `service1'.
>
> I think we could special-case that on the client side (in ‘herd’) with
> something like:
>
>   herd restart --batch s1 s2 s3
>
> which would restart those services one after the other.
>
> WDYT?

Oh, that could work, nice.  Maybe a little bit more generic?

--8<---------------cut here---------------start------------->8---
herd ACTION --batch s1 s2 s3 [-- args...]
--8<---------------cut here---------------end--------------->8---

Technically that prevents the user from batch-restarting service called
`--', but I would not be surprised if there would be some issues with
that already, so ¯\_(ツ)_/¯.

The default actions (restart, ...) still should probably signal an error
if they get arguments, people (me included) will forget the --batch from
time to time.

>
> Ludo’.

-- 
There are only two hard things in Computer Science:
cache invalidation, naming things and off-by-one errors.

[signature.asc (application/pgp-signature, inline)]

Message #17 received at 77109 <at> debbugs.gnu.org (full text, mbox):

From: Maxim Cournoyer <maxim.cournoyer <at> gmail.com>
To: Tomas Volf <~@wolfsden.cz>
Cc: 77109 <at> debbugs.gnu.org, Ludovic Courtès <ludo <at> gnu.org>
Subject: Re: bug#77109: [feature] [shepherd] Accept multiple services for
 actions
Date: Thu, 20 Mar 2025 12:16:56 +0900

Hi Tomas,

Tomas Volf <~@wolfsden.cz> writes:

> Maxim Cournoyer <maxim.cournoyer <at> gmail.com> writes:
>
>> Hi,
>>
>> Coming from a world where 'guix install package1 package2 ...' is a thing, I
>> sometimes would like to be able to do:
>>
>> herd restart service1 service2 ...
>>
>> Which Shepherd gladly accepts but disregarding service2 ...
>>
>> Would it be a good idea to teach the Shepherd how to do this?
>
> I guess it could be special-cased for start, stop, restart, since these
> three do not take (by default) any arguments (I *think* you can make
> `start' procedure taking arguments?  I have never tried.).  But for
> general case, the `service2' is passed as an argument to the action
> `restart' of service `service1'.

I think even special cased, it wouldn't be too surprising.  I've never
had a though of overriding the base actions for these to extend them in
what would be surprising ways ;-).

> I am not sure having different semantics for restart and any other
> action is a good idea though.
>
> But what I think would be a good idea is for start, stop, restart to
> signal an error when additional unexpected arguments are provided.

Failing to change the behavior as suggested, that would still be an
improvement, yes.  But then you'd also be special casing these actions,
as actions are designed to receive an arbitrary number of arguments and
cannot forcibly know which ones are really used/necessary in advance?

-- 
Thanks,
Maxim

Message #20 received at 77109 <at> debbugs.gnu.org (full text, mbox):

From: Tomas Volf <~@wolfsden.cz>
To: Maxim Cournoyer <maxim.cournoyer <at> gmail.com>
Cc: 77109 <at> debbugs.gnu.org, Ludovic Courtès <ludo <at> gnu.org>
Subject: Re: bug#77109: [feature] [shepherd] Accept multiple services for
 actions
Date: Fri, 21 Mar 2025 00:34:28 +0100

Maxim Cournoyer <maxim.cournoyer <at> gmail.com> writes:

>> I am not sure having different semantics for restart and any other
>> action is a good idea though.
>>
>> But what I think would be a good idea is for start, stop, restart to
>> signal an error when additional unexpected arguments are provided.
>
> Failing to change the behavior as suggested, that would still be an
> improvement, yes.  But then you'd also be special casing these actions,
> as actions are designed to receive an arbitrary number of arguments and
> cannot forcibly know which ones are really used/necessary in advance?

But the default implementation of `restart' knows it takes no arguments.
So something like the following.

--8<---------------cut here---------------start------------->8---
diff --git a/modules/shepherd/service.scm b/modules/shepherd/service.scm
index 79d14cf..68c4cca 100644
--- a/modules/shepherd/service.scm
+++ b/modules/shepherd/service.scm
@@ -1115,6 +1115,10 @@ the action."
       ;; Restarting is done in the obvious way.
       ((restart)
        (lambda (running . args)
+         (unless (null? args)
+           (local-output
+            (l10n "Action `restart' of ~a takes no arguments.")
+            (service-canonical-name service)))
          (let ((stopped-services (stop-service service)))
            (for-each start-service
                      (remove transient-service? stopped-services))
--8<---------------cut here---------------end--------------->8---

Dunno, just an (untested) idea. ¯\_(ツ)_/¯

Tomas

-- 
There are only two hard things in Computer Science:
cache invalidation, naming things and off-by-one errors.

Message #23 received at 77109 <at> debbugs.gnu.org (full text, mbox):

From: Tomas Volf <~@wolfsden.cz>
To: Maxim Cournoyer <maxim.cournoyer <at> gmail.com>
Cc: 77109 <at> debbugs.gnu.org, Ludovic Courtès <ludo <at> gnu.org>
Subject: Re: bug#77109: [feature] [shepherd] Accept multiple services for
 actions
Date: Fri, 21 Mar 2025 11:05:15 +0100

Actually, now that I think about it, why are formal arguments for the
restart lambda `(running . args)'?  For example status has just `(_)'.
Neither `running' nor `args' are used in the lambda itself.

Changing the formal arguments to simply _ would get us the same behavior
you get when you try to invoke e.g. status action with multiple
arguments (an error).

Ludovic, any opinions here?

Tomas

-- 
There are only two hard things in Computer Science:
cache invalidation, naming things and off-by-one errors.

Message #26 received at 77109 <at> debbugs.gnu.org (full text, mbox):

From: Ludovic Courtès <ludo <at> gnu.org>
To: Tomas Volf <~@wolfsden.cz>
Cc: 77109 <at> debbugs.gnu.org, Maxim Cournoyer <maxim.cournoyer <at> gmail.com>
Subject: Re: bug#77109: [feature] [shepherd] Accept multiple services for
 actions
Date: Fri, 21 Mar 2025 23:53:08 +0100

Tomas Volf <~@wolfsden.cz> skribis:

> Actually, now that I think about it, why are formal arguments for the
> restart lambda `(running . args)'?  For example status has just `(_)'.
> Neither `running' nor `args' are used in the lambda itself.
>
> Changing the formal arguments to simply _ would get us the same behavior
> you get when you try to invoke e.g. status action with multiple
> arguments (an error).

I think it’s a bug.  Back in the day (commit
a84ecf34be2a35e8b068d4232d8932acc5986c33) would pass those extra
arguments to ‘start’:

--8<---------------cut here---------------start------------->8---
      ((restart)
       (lambda (running . args)
         (if running
             (stop obj)
             (local-output "~a was not running." (canonical-name obj)))
         (start obj args)))
--8<---------------cut here---------------end--------------->8---

Which is consistent and should probably be restored.

That way, we’d get an error when restarting services that take no
arguments.

Ludo’.

Message #29 received at 77109 <at> debbugs.gnu.org (full text, mbox):

From: Ludovic Courtès <ludo <at> gnu.org>
To: Tomas Volf <~@wolfsden.cz>
Cc: 77109 <at> debbugs.gnu.org, Maxim Cournoyer <maxim.cournoyer <at> gmail.com>
Subject: Re: bug#77109: [feature] [shepherd] Accept multiple services for
 actions
Date: Sat, 22 Mar 2025 19:49:34 +0100

Ludovic Courtès <ludo <at> gnu.org> skribis:

> Tomas Volf <~@wolfsden.cz> skribis:
>
>> Actually, now that I think about it, why are formal arguments for the
>> restart lambda `(running . args)'?  For example status has just `(_)'.
>> Neither `running' nor `args' are used in the lambda itself.
>>
>> Changing the formal arguments to simply _ would get us the same behavior
>> you get when you try to invoke e.g. status action with multiple
>> arguments (an error).
>
> I think it’s a bug.  Back in the day (commit
> a84ecf34be2a35e8b068d4232d8932acc5986c33) would pass those extra
> arguments to ‘start’:
>
>       ((restart)
>        (lambda (running . args)
>          (if running
>              (stop obj)
>              (local-output "~a was not running." (canonical-name obj)))
>          (start obj args)))
>
> Which is consistent and should probably be restored.

Done in 3ab3930a30495391e5176355e524a8dc026bd060.

Ludo’.

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