Re: [systemd-devel] Still confused with socket activation
04.02.2021 17:53, Simon McVittie пишет: > On Thu, 04 Feb 2021 at 13:07:33 +0100, Reindl Harald wrote: >> "Requires=a.service" combined with "Before=a.service" is contradictory - >> don't you get that? > > It means what it says: whenever my service is enabled, a.service must > also be enabled, but my service has to start first (and stop last). > Nitpicking - you probably mean "activated", not "enabled". "enabled" means something entirely different in systemd (at least above config directives are not related to "enabling" unit). > For instance, imagine this scenario: > > * my service sets something up that will trigger an action later: > perhaps it creates a configuration fragment in a.conf.d > > * any number of other services might be doing the same as my service > > * whenever at least one service has done that, when they have all finished > doing their setup, we need to start a.service, which will take those > triggers (e.g. contents of a.conf.d) and "commit" whatever is needed > for all of them > > * if multiple services have set up a triggered action, we only want to > run a.service once, and it will act on all the triggers as a batch > This is racy. If one of other services is activated when a.service is already being activated due to other service, it is unpredictable whether a.service will pick changes made by all other services. The only way to ensure that all other services are being activated together with (and finished before) a.service is to have a.service Wants(Requires)/After them (or WantedBy(RequiredBy)=a.service in all of them). > Then my service should have Requires=a.service (because if a.service > never runs, the "commit" action will never happen and my service will > not do what I wanted); and it should have Before=a.service (because the > triggers need to be in place before a.service processes them). > If you never activate a.service explicitly you also never know whether it completed successfully or not. You only have status of "some other service" and it will fail only if a.service definition is missing; it won't tell you anything about result of a.service itself. While this is interesting exercise, it is really stretching systemd dependency systems way beyond what it was deigned for. > dpkg and RPM triggers are not (currently!) systemd services, but they > work a lot like this. They're typically used to regenerate caches. > > Another reason to combine Requires with Before is that Before is really > a short name for "start before and stop after", and After is really a > short name for "start after and stop before". If you're dealing with > actions taken during system shutdown or session logout, the stop action > might be the one that does the real work, making it more likely that > Before dependencies are the important ones. > > smcv > ___ > systemd-devel mailing list > systemd-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/systemd-devel > ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Still confused with socket activation
On Thu, 2021-02-04 at 22:16 +0300, Andrei Borzenkov wrote: > 03.02.2021 22:25, Benjamin Berg пишет: > > Requires= actually has the difference that the unit must become > > part of > > the transaction (if it is not active already). So you get a hard > > failure and appropriate logging if the unit cannot be added to the > > transaction for some reason. > > > > Oh, I said "documented" :) systemd documentation does not even define > what "transaction" is. You really need to know low level implementation > details to use it in this way. > > But thank you, I missed this subtlety. Of course another reason could be > stop behavior. Oh, good point! I really had not been considering the implication on stop behaviour. :) Benjamin > > > Care to show more complete example and explain why Wants does not > > > work in this case? > > > > Wants= would work fine. I think it boils down to whether you find > > the > > extra assertions useful. The Requires= documentation actually > > suggests > > using Wants= exactly to avoid this. > > > > Benjamin > > > > signature.asc Description: This is a digitally signed message part ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Still confused with socket activation
03.02.2021 22:25, Benjamin Berg пишет: > On Wed, 2021-02-03 at 20:47 +0300, Andrei Borzenkov wrote: >> 03.02.2021 00:25, Benjamin Berg пишет: >>> On Tue, 2021-02-02 at 22:50 +0300, Andrei Borzenkov wrote: 02.02.2021 17:59, Lennart Poettering пишет: > > Note that Requires= in almost all cases should be combined with > an > order dep of After= onto the same unit. Years ago I asked for example when Requires makes sense without After. Care to show it? I assume you must have use case if you say "in almost all". >>> >>> In the GNOME systemd units there are a few places where a Requires= >>> is >>> combined with Before=. >>> >> >> This is functionally completely equivalent to simply using >> Wants+Before. >> At least as long as you rely on *documented* functions. > > Requires= actually has the difference that the unit must become part of > the transaction (if it is not active already). So you get a hard > failure and appropriate logging if the unit cannot be added to the > transaction for some reason. > Oh, I said "documented" :) systemd documentation does not even define what "transaction" is. You really need to know low level implementation details to use it in this way. But thank you, I missed this subtlety. Of course another reason could be stop behavior. >> Care to show more complete example and explain why Wants does not >> work in this case? > > Wants= would work fine. I think it boils down to whether you find the > extra assertions useful. The Requires= documentation actually suggests > using Wants= exactly to avoid this. > > Benjamin > signature.asc Description: OpenPGP digital signature ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Still confused with socket activation
On Thu, 04 Feb 2021 at 13:07:33 +0100, Reindl Harald wrote: > "Requires=a.service" combined with "Before=a.service" is contradictory - > don't you get that? It means what it says: whenever my service is enabled, a.service must also be enabled, but my service has to start first (and stop last). For instance, imagine this scenario: * my service sets something up that will trigger an action later: perhaps it creates a configuration fragment in a.conf.d * any number of other services might be doing the same as my service * whenever at least one service has done that, when they have all finished doing their setup, we need to start a.service, which will take those triggers (e.g. contents of a.conf.d) and "commit" whatever is needed for all of them * if multiple services have set up a triggered action, we only want to run a.service once, and it will act on all the triggers as a batch Then my service should have Requires=a.service (because if a.service never runs, the "commit" action will never happen and my service will not do what I wanted); and it should have Before=a.service (because the triggers need to be in place before a.service processes them). dpkg and RPM triggers are not (currently!) systemd services, but they work a lot like this. They're typically used to regenerate caches. Another reason to combine Requires with Before is that Before is really a short name for "start before and stop after", and After is really a short name for "start after and stop before". If you're dealing with actions taken during system shutdown or session logout, the stop action might be the one that does the real work, making it more likely that Before dependencies are the important ones. smcv ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Still confused with socket activation
On Thu, 2021-02-04 at 13:07 +0100, Reindl Harald wrote: > Am 04.02.21 um 12:46 schrieb Benjamin Berg: > > On Wed, 2021-02-03 at 16:43 +0100, Reindl Harald wrote: > > > seriously - explain what you expect to happen in case of > > > > > > Requires=a.service > > > Before=a.service > > > > > > except some warning that it's nonsense > > > > So, one way I used it is as ExecStartPost= equivalent for a .target > > unit. i.e. pull in a Type=oneshot service once a target has become > > active in order to execute a simple command > > "Requires=a.service" combined with "Before=a.service" is > contradictory - > don't you get that? Your statements will not become more informed by repeating them. It looks to me like you are interpreting Requires= incorrectly. Of course, one can see a contradiction in saying "B requires A in order to run" and then also saying "start A after B is ready". But systemd considers requirements and ordering as two independent problems. As such "Requires=A" only means something like "unit A must be added to the transaction together with B". A statement that does not imply ordering. Yes, this is a a very logical/mathematical meaning which may not be what you intuitively expect. And it does have the unfortunate side effect of sometimes confusing people and they forget to add a needed After= that they thought was implied. But, it is well defined what happens when combining Requires= with Before=. There is no contradiction. Benjamin signature.asc Description: This is a digitally signed message part ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Still confused with socket activation
Am 04.02.21 um 12:46 schrieb Benjamin Berg: On Wed, 2021-02-03 at 16:43 +0100, Reindl Harald wrote: seriously - explain what you expect to happen in case of Requires=a.service Before=a.service except some warning that it's nonsense So, one way I used it is as ExecStartPost= equivalent for a .target unit. i.e. pull in a Type=oneshot service once a target has become active in order to execute a simple command "Requires=a.service" combined with "Before=a.service" is contradictory - don't you get that? ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Still confused with socket activation
On Wed, 2021-02-03 at 16:43 +0100, Reindl Harald wrote: > seriously - explain what you expect to happen in case of > > Requires=a.service > Before=a.service > > except some warning that it's nonsense So, one way I used it is as ExecStartPost= equivalent for a .target unit. i.e. pull in a Type=oneshot service once a target has become active in order to execute a simple command. Benjamin signature.asc Description: This is a digitally signed message part ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Still confused with socket activation
On Wed, 2021-02-03 at 20:47 +0300, Andrei Borzenkov wrote: > 03.02.2021 00:25, Benjamin Berg пишет: > > On Tue, 2021-02-02 at 22:50 +0300, Andrei Borzenkov wrote: > > > 02.02.2021 17:59, Lennart Poettering пишет: > > > > > > > > Note that Requires= in almost all cases should be combined with > > > > an > > > > order dep of After= onto the same unit. > > > > > > Years ago I asked for example when Requires makes sense without > > > After. > > > Care to show it? I assume you must have use case if you say "in > > > almost all". > > > > In the GNOME systemd units there are a few places where a Requires= > > is > > combined with Before=. > > > > This is functionally completely equivalent to simply using > Wants+Before. > At least as long as you rely on *documented* functions. Requires= actually has the difference that the unit must become part of the transaction (if it is not active already). So you get a hard failure and appropriate logging if the unit cannot be added to the transaction for some reason. > Care to show more complete example and explain why Wants does not > work in this case? Wants= would work fine. I think it boils down to whether you find the extra assertions useful. The Requires= documentation actually suggests using Wants= exactly to avoid this. Benjamin signature.asc Description: This is a digitally signed message part ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Still confused with socket activation
03.02.2021 21:13, Andrei Borzenkov пишет: > 02.02.2021 12:43, Ulrich Windl пишет: >> Hi! >> >> Having: >> --- >> # /usr/lib/systemd/system/virtlockd.service >> [Unit] >> Description=Virtual machine lock manager >> Requires=virtlockd.socket >> Requires=virtlockd-admin.socket > > That's always wrong with After for the same units s/with/without/ ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Still confused with socket activation
02.02.2021 12:43, Ulrich Windl пишет: > Hi! > > Having: > --- > # /usr/lib/systemd/system/virtlockd.service > [Unit] > Description=Virtual machine lock manager > Requires=virtlockd.socket > Requires=virtlockd-admin.socket That's always wrong with After for the same units unless you can prove that both socket units are always ordered Before service unit due to dependency chain, at least if intention is to ensure socket units are active *before* service unit. In real life nobody notices it because both sockets are started much earlier which papers over race condition. And if after 10 years of software existence everyone still gets it wrong I strongly suspect something is not right with software, not with everyone. > Before=libvirtd.service > ... > --- > > How would I start both sockets successfully unter program control? I do not understand what you want to say here, sorry. What "program control" means? What exactly are you trying to do? > If I start one socket, I cannot start the other without an error (as > libvirtd.service is running already, see my earlier message from last week). I do not see how starting socket unit is related to starting service unit. Unless there was incoming traffic on socket. Also I do not understand why you need to start socket units if you *already* started service unit. Again, you do not really provide much coherent information to do any suggestion. And I do not really understand the reason to use two different socket units that apparently are always started together and activate the same service. Just create single socket unit that listens on both sockets. > If I mask the socket units, I cannot start the libvirtd.service. > So would I disable the socket units and start libvirtd.service? You misunderstand what "disable" means in systemd (see remark above). You cannot disable (in common sense) starting of socket units together with virtlockd.service because starting of virtlockd.service will always attempt to start both socket units (that is exactly what Requires/Wants are about). Actually if they are "enabled" (in systemd sense) then they are started very early during boot, long before service unit. What exact problem you have in this case? > Unfortunately if someone (update when vendor-preset is enabled) re-enables > the socket units, it would break things, so I tried to mask them, but that > failed, too. > error: Could not issue start for prm_virtlockd: Unit virtlockd.socket is > masked. > > Regards, > Ulrich > > > > > ___ > systemd-devel mailing list > systemd-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/systemd-devel > ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Still confused with socket activation
03.02.2021 00:25, Benjamin Berg пишет: > On Tue, 2021-02-02 at 22:50 +0300, Andrei Borzenkov wrote: >> 02.02.2021 17:59, Lennart Poettering пишет: >>> >>> Note that Requires= in almost all cases should be combined with an >>> order dep of After= onto the same unit. >> >> Years ago I asked for example when Requires makes sense without >> After. >> Care to show it? I assume you must have use case if you say "in >> almost all". > > In the GNOME systemd units there are a few places where a Requires= is > combined with Before=. > This is functionally completely equivalent to simply using Wants+Before. At least as long as you rely on *documented* functions. Care to show more complete example and explain why Wants does not work in this case? signature.asc Description: OpenPGP digital signature ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Still confused with socket activation
Am 03.02.21 um 10:43 schrieb Benjamin Berg: On Wed, 2021-02-03 at 08:00 +0100, Reindl Harald wrote: Am 02.02.21 um 22:25 schrieb Benjamin Berg: On Tue, 2021-02-02 at 22:50 +0300, Andrei Borzenkov wrote: 02.02.2021 17:59, Lennart Poettering пишет: Note that Requires= in almost all cases should be combined with an order dep of After= onto the same unit. Years ago I asked for example when Requires makes sense without After. Care to show it? I assume you must have use case if you say "in almost all". In the GNOME systemd units there are a few places where a Requires= is combined with Before= sounds like complete nonsense you can not require something at your own to be there but on the other hand start before it - at least by common sense The units are indeed non-trivial. I have put in a lot of effort to find a solution that both works and is robust in various failure modes. It may well be that there is a better approach with similar properties. But, session login and logout(!) is not quite as trivial as one could hope for unfortunately (backward compatibility and workarounds add some complexities). So, I would love to be educated on how to simplify all this while still catching the various corner cases. But in order to convince me, you'll need to make a more concrete suggestion and explain its properties seriously - explain what you expect to happen in case of Requires=a.service Before=a.service except some warning that it's nonsense you need a.service but want to be started before a.service sounds like wash me but don't make me wet ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Still confused with socket activation
On Wed, 2021-02-03 at 08:00 +0100, Reindl Harald wrote: > > > Am 02.02.21 um 22:25 schrieb Benjamin Berg: > > On Tue, 2021-02-02 at 22:50 +0300, Andrei Borzenkov wrote: > > > 02.02.2021 17:59, Lennart Poettering пишет: > > > > > > > > Note that Requires= in almost all cases should be combined with > > > > an > > > > order dep of After= onto the same unit. > > > > > > Years ago I asked for example when Requires makes sense without > > > After. > > > Care to show it? I assume you must have use case if you say "in > > > almost all". > > > > In the GNOME systemd units there are a few places where a Requires= > > is > > combined with Before= > > sounds like complete nonsense > > you can not require something at your own to be there but on the other > hand start before it - at least by common sense The units are indeed non-trivial. I have put in a lot of effort to find a solution that both works and is robust in various failure modes. It may well be that there is a better approach with similar properties. But, session login and logout(!) is not quite as trivial as one could hope for unfortunately (backward compatibility and workarounds add some complexities). So, I would love to be educated on how to simplify all this while still catching the various corner cases. But in order to convince me, you'll need to make a more concrete suggestion and explain its properties. Benjamin signature.asc Description: This is a digitally signed message part ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Still confused with socket activation
Am 02.02.21 um 22:25 schrieb Benjamin Berg: On Tue, 2021-02-02 at 22:50 +0300, Andrei Borzenkov wrote: 02.02.2021 17:59, Lennart Poettering пишет: Note that Requires= in almost all cases should be combined with an order dep of After= onto the same unit. Years ago I asked for example when Requires makes sense without After. Care to show it? I assume you must have use case if you say "in almost all". In the GNOME systemd units there are a few places where a Requires= is combined with Before= sounds like complete nonsense you can not require something at your own to be there but on the other hand start before it - at least by common sense ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Still confused with socket activation
On Tue, 2021-02-02 at 22:50 +0300, Andrei Borzenkov wrote: > 02.02.2021 17:59, Lennart Poettering пишет: > > > > Note that Requires= in almost all cases should be combined with an > > order dep of After= onto the same unit. > > Years ago I asked for example when Requires makes sense without > After. > Care to show it? I assume you must have use case if you say "in > almost all". In the GNOME systemd units there are a few places where a Requires= is combined with Before=. Benjamin signature.asc Description: This is a digitally signed message part ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Still confused with socket activation
On Di, 02.02.21 22:50, Andrei Borzenkov (arvidj...@gmail.com) wrote: > 02.02.2021 17:59, Lennart Poettering пишет: > > > > Note that Requires= in almost all cases should be combined with an > > order dep of After= onto the same unit. > > Years ago I asked for example when Requires makes sense without After. > Care to show it? I assume you must have use case if you say "in almost all". You can synthesize cases where it doesn't matter: if you know the order is enforced by other means already, for example transitive ordering. i.e. think of a late-boot service that needs some early-boot preparation service to have run. Because the early-boot service probably ordered itself before sysinit.target, and the late-boot service is implicitly ordered after basic.target, there isn' a need to order them directly against each other too, the transient deps between sysinit.target and basic.target already gurantee correct ordering. And there are other cases: for example if the ordering is already configured the other way, or if you have any other reason you know the stuff is ordered already. Lennart -- Lennart Poettering, Berlin ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Still confused with socket activation
02.02.2021 17:59, Lennart Poettering пишет: > > Note that Requires= in almost all cases should be combined with an > order dep of After= onto the same unit. Years ago I asked for example when Requires makes sense without After. Care to show it? I assume you must have use case if you say "in almost all". ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Still confused with socket activation
On Di, 02.02.21 10:43, Ulrich Windl (ulrich.wi...@rz.uni-regensburg.de) wrote: > Hi! > > Having: > --- > # /usr/lib/systemd/system/virtlockd.service > [Unit] > Description=Virtual machine lock manager > Requires=virtlockd.socket > Requires=virtlockd-admin.socket > Before=libvirtd.service > ... > --- > > How would I start both sockets successfully unter program control? > If I start one socket, I cannot start the other without an error (as > libvirtd.service is running already, see my earlier message from last week). > If I mask the socket units, I cannot start the libvirtd.service. > So would I disable the socket units and start libvirtd.service? > Unfortunately if someone (update when vendor-preset is enabled) re-enables > the socket units, it would break things, so I tried to mask them, but that > failed, too. > error: Could not issue start for prm_virtlockd: Unit virtlockd.socket is > masked. I don't grok what you are trying to say, the excerpt of the unit file is too short. Please provide the relevant parts of the other unit files too. Masking is a big hammer, the last resort. It should not be part of the usual workflow. Note that Requires= in almost all cases should be combined with an order dep of After= onto the same unit. If the unit above doesn't do that it's almost certainly broken. Lennart -- Lennart Poettering, Berlin ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
[systemd-devel] Still confused with socket activation
Hi! Having: --- # /usr/lib/systemd/system/virtlockd.service [Unit] Description=Virtual machine lock manager Requires=virtlockd.socket Requires=virtlockd-admin.socket Before=libvirtd.service ... --- How would I start both sockets successfully unter program control? If I start one socket, I cannot start the other without an error (as libvirtd.service is running already, see my earlier message from last week). If I mask the socket units, I cannot start the libvirtd.service. So would I disable the socket units and start libvirtd.service? Unfortunately if someone (update when vendor-preset is enabled) re-enables the socket units, it would break things, so I tried to mask them, but that failed, too. error: Could not issue start for prm_virtlockd: Unit virtlockd.socket is masked. Regards, Ulrich ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
