Re: [systemd-devel] sd_bus_get_unique_name returns -EBADMSG or -EBUSY
On Wed, 7 Apr 2021 16:15:40 +0200 Lennart Poettering wrote: > > > As you stated in the linked email, there is no global state. > > So, I suppose that if I call any sd_bus_* function that > > all that I have to take into account is that the data > > that is passed to those functions is protected. If they > > use different connections, then no data should be shared, > > no? > > Not sure I grok the question. It was just a repeat, stated differently. I assume that anything related to the same sd_bus* object, which includes sd_bus_message* objects that use that sd_bus* can not be passed to more than one function at a time and executed in parallel. But (which is what I stated above) if the (associated) sd_bus* is different, then that is possible. I think you already confirmed that this is possible. So, my plan will be to add a "lock" per connection. I have dbus::Connection objects and it will be very clear which one any call to a sd_bus_* function is associated with; so I can use those objects as "lock". I put lock between quotes here because it won't be an ordinary mutex: a mutex blocks other threads as long as the thread holds this mutex (aka, is inside the function). That is quite long imho: normally I try to keep mutexes that can block out other threads for (much) less than a micro second. Longer than 10 micro seconds is unacceptable (and wrong use of mutexes imho). I invented a different concept to deal with threads with my library: I run threaded code in 'tasks' which are then basically executed single-threaded (not the same thread, but one thread at a time runs a task). All variables that a task deals with while running are private members of the task object and there is therefore no locking needed at all for those variables. However, I decided against using a different sdbus connection per thread for the simple reason that I do not keep track of threads; I have tasks that when needing to run get cpu time from an available thread. I could use one connection per task, but that has (a lot of) overhead, since I create, execute and destroy tasks a LOT. Aka, you'd get a new connection for every sd_bus message. It seemed more logical to me to make a connection and keep that alive; and reuse it over and over for new messages. That way, in most cases, I'll just have a single connection (ie, to the userbus) without a repeat of the handshake all the time. But since I have tasks for doing everything, like sending a signal, or a method call, and those run in parallel at the moment, the connection, aka sd_bus object, is used by multiple threads concurrently at the moment, causing more than one thread to enter the sd_bus library at the time time for the same sd_bus object. ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] sd_bus_get_unique_name returns -EBADMSG or -EBUSY
On Mi, 07.04.21 12:17, Carlo Wood (ca...@alinoe.com) wrote: > On Tue, 6 Apr 2021 18:41:21 +0200 > Lennart Poettering wrote: > > > EBADMSG usually means that somehow an invalid dbus packet we couldn't > > parse entered the stream. maybe some memory corruption thing? or maybe > > you are using this in a threaded env without locking? > > > > Lennart > > Yes, that is the case. I was reading up on the demands, > which I found on > https://www.spinics.net/lists/systemd-devel/msg01779.html > > making me wonder why I went through the trouble of supporting > dbus with my library :p (which aims at massive parallel > execution without EVER blocking or going to sleep). sd-bus is fully async. It only blocks if you call the functions that are synchronous wrappers around async functions. e.g. sd_bus_call() is actually more or less a synchronous wrapper around the same stuff that sd_bus_call_async() does async. Async means here the work is enqueued into the socket or client side, and then dispatched by an event loop of sorts. The event loop can be sd-event, or you can use any other you like, that has a poll()-like glue interface. You are supposed to have one sd-bus connection per thread though. It's the model this is all built for. If you want to share one connection among multiple threads, you need to do your locking around that yourself. > Libraries that do not support threading are a pain :/. Well, depends what you mean by "supporting". sd-bus is written with threads in mind, i.e. everything is broken down to local contexts, there's no global non-fixed data and such. It's just a different model that you might be used to: i.e. one connection per thread and locking if desired must be done in your own code. > It would really help if you could tell me a more fine- > grained multi-threading demands; like - per connection. D-Bus as a protocol is big on global ordering. It's thus not really compatible with being dispatched in thread pools, because those would basically randomize dispatch ordering. It's a design decision of D-Bus. > Surely I can execute sd_bus_* functions that deal with > a different dbus* in parallel? Yes. You are not supposed to share individual sd_bus objects (and their associated helper objects) between multiple threads, unless you do your own locking around it. But you can have as many sd_bus objects you want and run the independently from any number of threads you like, fully in parallel. > As you stated in the linked email, there is no global state. > So, I suppose that if I call any sd_bus_* function that > all that I have to take into account is that the data > that is passed to those functions is protected. If they > use different connections, then no data should be shared, > no? Not sure I grok the question. Lennart -- Lennart Poettering, Berlin ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] hostnamectl set-hostname non-admin user
Thanks Silvio! That's just what I needed.
Cheers,
-Damien
On Tue, Apr 6, 2021 at 9:26 PM Silvio Knizek wrote:
> Am Dienstag, dem 06.04.2021 um 16:21 +0300 schrieb Damien LEFEVRE:
> > Hi,
> >
> > I have an embedded device and I do not install sudo. I need to have a
> > non-root running the main service capable of changing the hostname.
> >
> > After spending a long afternoon on this I still have not managed.
> >
> > Here i've tried adding my new user but only read-only requests go
> > through
> > /usr/share/dbus-1/system.d/org.freedesktop.hostname1.conf
> > ```xml
> >
> > > Configuration 1.0//EN"
> >
> > "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd;>
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > ```
> >
> >
> > /usr/share/polkit-1/actions/org.freedesktop.hostname1.policy
> > ```xml
> >
> > > Configuration 1.0//EN"
> > "
> > http://www.freedesktop.org/standards/PolicyKit/1/policyconfig.dtd;>
> >
> >
> >
> >
> >
> > The systemd Project
> >
> > http://www.freedesktop.org/wiki/Software/systemd > url>
> >
> >
> > Set host
> > name
> > Authentication is
> > required to set the local host name.
> >
> > auth_admin_keep
> >
> > auth_admin_keep
> > auth_admin_keep
> >
> >
> >
> >
> > Set static host
> > name
> > Authentication is
> > required to set the statically configured local host name, as well as
> > the pretty host name.
> >
> > auth_admin_keep
> >
> > auth_admin_keep
> > auth_admin_keep
> >
> > > key="org.freedesktop.policykit.imply">org.freedesktop.hostname1.set-
> > hostname org.freedesktop.hostname1.set-machine-info
> >
> >
> >
> > Set machine
> > information
> > Authentication is
> > required to set local machine information.
> >
> > auth_admin_keep
> >
> > auth_admin_keep
> > auth_admin_keep
> >
> >
> >
> >
> > Get product
> > UUID
> > Authentication is
> > required to get product UUID.
> >
> > auth_admin_keep
> >
> > auth_admin_keep
> > auth_admin_keep
> >
> >
> >
> >
> > ```
> >
> > Despite all my attempts I always get 'Could not set property: Access
> > denied' for hostnamectl set-hostname
> >
> > And get the 'org.freedesktop.DBus.Error.AccessDenied' in dbus-monitor
> >
> > method call time=1617739342.317948 sender=:1.23 ->
> > destination=org.freedesktop.hostname1 serial=3
> > path=/org/freedesktop/hostname1; interface=org.freedesktop.hostname1;
> > member=SetStaticHostname
> >string "blabla"
> >boolean true
> > ...
> > error time=1617739342.320289 sender=:1.24 -> destination=:1.23
> > error_name=org.freedesktop.DBus.Error.AccessDenied reply_serial=3
> >string "Permission denied"
> >
> >
> > Any help would be greatly appreciated =)
> >
> > -Damien
>
> Hi Damien,
>
> you actually need to configure polkit for this. Something like
> /etc/polkit-1/rules.d/49-allow-myuser-access-to-hostnamed.rules
>
> ```javascript
> polkit.addRule(function(action, subject) {
> if (action.id == "org.freedesktop.hostname1.set-hostname") {
> if (subject.user == "myuser") {
> return polkit.Result.YES;
> }
> }
> });
> ```
>
> Your dbus definition only says that one can define rules including such
> actions.
>
> HTH
> Silvio
>
> ___
> systemd-devel mailing list
> systemd-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/systemd-devel
>
___
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Re: [systemd-devel] sd_bus_get_unique_name returns -EBADMSG or -EBUSY
On Tue, 6 Apr 2021 18:41:21 +0200 Lennart Poettering wrote: > EBADMSG usually means that somehow an invalid dbus packet we couldn't > parse entered the stream. maybe some memory corruption thing? or maybe > you are using this in a threaded env without locking? > > Lennart Yes, that is the case. I was reading up on the demands, which I found on https://www.spinics.net/lists/systemd-devel/msg01779.html making me wonder why I went through the trouble of supporting dbus with my library :p (which aims at massive parallel execution without EVER blocking or going to sleep). Libraries that do not support threading are a pain :/. It would really help if you could tell me a more fine- grained multi-threading demands; like - per connection. Surely I can execute sd_bus_* functions that deal with a different dbus* in parallel? As you stated in the linked email, there is no global state. So, I suppose that if I call any sd_bus_* function that all that I have to take into account is that the data that is passed to those functions is protected. If they use different connections, then no data should be shared, no? Carlo ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
