Discussion:
Storing Data on systemd bus
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guhan balasubramanian
2017-02-06 20:54:57 UTC
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Hi,

I've followed the tutorial on the 0pointer blog [1] for creating a 'system'
service.
I am currently held up with two questions which would help me come up with
a better design for my "inventory" program.

1. Is it possible to use sd-bus API as an inventory to store and
retrieve data? Whether sd-bus internally would store the data in the bus
forever until deleted, something like a message queue?
2. If above question has a positive answer, I am trying to get and set
properties by creating a service (Example 1 in Reference - Busctl Man
Page <https://www.freedesktop.org/software/systemd/man/busctl.html>). I
am doing this on the system bus, but I am not able to '*store the data
in the bus'* as in the example. For now, I am only able to store data in
the '*process memory' *as global variables. [2] doesn't seem to help
much as the bus is not storing the data using SD_BUS_WRITABLE_PROPERTY. Is
there a reference code or documentation I can refer to?

Please advise and thanks in advance!

-Guhan

References:
1. http://0pointer.net/blog/the-new-sd-bus-api-of-systemd.html
2.
https://github.com/systemd/systemd/blob/master/src/libsystemd/sd-bus/test-bus-objects.c
Lennart Poettering
2017-02-06 20:58:52 UTC
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Post by guhan balasubramanian
Hi,
I've followed the tutorial on the 0pointer blog [1] for creating a 'system'
service.
I am currently held up with two questions which would help me come up with
a better design for my "inventory" program.
1. Is it possible to use sd-bus API as an inventory to store and
retrieve data? Whether sd-bus internally would store the data in the bus
forever until deleted, something like a message queue?
D-Bus is an IPC system, for delivering control messages between
processes.

It's not a storage system, and while messages are queued on it, you
cannot read them out of order, the messages have to be "small", and
you will be kicked off the bus if you stop processing your incoming
messages for too long.

Lennart
--
Lennart Poettering, Red Hat
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