[Buildroot] [PATCH v2] package/dbusbroker: new package

Yann E. MORIN yann.morin.1998 at free.fr
Sun Jun 14 13:10:13 UTC 2020

Norbert, All,

On 2020-06-12 09:02 +0200, Norbert Lange spake thusly:
> Am Fr., 12. Juni 2020 um 07:32 Uhr schrieb Yann E. MORIN
> <yann.morin.1998 at free.fr>:
> >
> > Thanks for this new improved version. :-)
> >
> > I still have a few concerns about it, see below...
> >
> > On 2020-06-11 01:24 +0200, Norbert Lange spake thusly:
> > > Add dbus-broker, which is a drop-in replacement
> > > for the dbus-daemon.
> >
> > Sorry, but this commit log is far from enough. See below for all the
> > pieces I find are missing.
> >
> > A commit log is not here to describe what is being done, but why it
> > is being done. It is here so that the others can understand it. The
> > more details you can add (up to a certain externt, of course!), the
> > easier the patch can be reviewed, especially when there are
> > misundersstanding like what I provided in my own submission.
> Yes, I hoped you could merge this from your version, which I commented BTW.
> I have more a problem with the workflow of the ML, especially if someone
> "branches out" with another patch.

When I am suggesting an alternate solution, but I have some doubts about
it, I would usually take the original patch, massage it into my idea of
what it should look like, test it, and resubmit to make my point.

Then the original submitter (and others!) have a way to see the point,
and comment further by providing additional review and explanations on
why the alternate proposal is not correct.

Eventually, the original submitter can further improve by keeping the
good pieces, removing the bad ones, and so on... and resubmit a new

So you are very welcome to have re-spun this new iteration. :-)

> > The commit log also misses the explanations about the licensing
> > information. This is *very* important to have, because it is not
> > obvious hy the terms are as they are, and wh we have two files for
> > each sub-projects. You could have simply duplicated what I wrote
> > in my own submission.
> Yes, I am not up to speed about commit-log stuff, and I usually
> keep explanations where the code is.

Usually, we like the nitty-gritty details in the commit log, for
posterity, while we keep the comments in the code to the bare minimal.

In this case, the licensing dirtiness should be kept in the commit log,
and a comment could be added in the .mk, like:

    # Inconsistency between AUTHORS and README, keep both, and
    # interpret as per the README

> > Finally, the folowing, from here [*]:
> >
> > > bases on Yanns changes, and
> > > -   add an own config entry for dbus-broker-launch
> > >     enabled by default if systemd init is used
> >
> > We usually do not enable options by default. But see below...
> >
> >
> > So, I see you don;t like it, but BR2_COREUTILS_HOST_DEPENDENCY is
> > already a dependency of systemd, so adding it to dbus-broker is not in
> > fact adding any new build-time overhead. And if your build machine has a
> > recent-enough, BR2_COREUTILS_HOST_DEPENDENCY will be empty already.
> There is still the point of keeping things simple, and I dont get why
> ../dbus.socket
> cant be used, instead of an gnu-specific option.

I tend to like it better that we use it, because this makes it explicit.

Also, there is always the ambiguity about what a relative symlink means
when created: is it relative to the current working directory, or
relative to the symlink itself?

And since we already anyway are sure we do have it (either from the host
or as a dependency of systemd itself), let's just use it...

And BTW, we do not explicitly support building on a non-GNU system
anyway, so it being a GNU extension is moot (IMHO).

> > > -   undo adding dbus user - never used by this package
> >
> > So, how does the does the message bus daemon runs as non-root? In the
> > original dbus pakcage, we define a user, that is used to switch the
> > mesage bus to run as non-root. Pleas explain why the user is nopt
> > needed.
> Ok,  I take everything back.
> I thought this was handled in the service files by adding isolation options
> (as systemd does the "launching"). Seems like it does drop to the uid,
> dunno what I tested months ago when first created that package

OK, I knew that would have been systemd doing the uid-drop, by I'd still
like the info appear somewhere (so that we do not later question this in
light of the original dbus package which defines one).

> > Why do you add an option to enable the launcher? Just do it
> > unconditionally when systemd is enabled. And select expat as I did in my
> > own patch, in the main symbol:
> Well, my first attempt was to only make dbus-broker(-launch) available
> with systemd,
> given that there is probably no one using it differently yet.
> If you argue that it makes sense to provide the plain dbus-broker,
> then it makes sense doing so with systemd aswell.
> (see below, I use system without dbus or dbus-broker-launch).

I guess you meant 'systemd' in that last sentence.

But OK, I would be fine to introduce this package as a systemd-only
option for now, until someone actually provides a non-systemd launcher.

So, we would still not need an extra option, but just:

        bool "dbus-broker"
        depends on BR2_USE_MMU
        depends on BR2_TOOLCHAIN_HAS_THREADS
        depends on BR2_PACKAGE_SYSTEMD
        select BR2_PACKAGE_EXPAT

And explain in the commit log that the launcher needs systemd, and that
without the launcher there is no point in dbus-broker.

> > So, in addition to all the above, this patch is lacking two other things
> > that I did provide:
> >
> >   - switching systemd to work with dbus-broker (rather than whining
> >     about it in the commit log;
> I got a patch series for systemd, just a matter of finding the time
> (and retesting).
> But I would just simply *take out* the dependency to DBUS
> ( and UTIL_LINUX_BINARIES and UTIL_LINUX_NOLOGIN, getting a systemd
> rootfs below 20MB).
> I have been running systemd without either for more than a year.
> What would be your pick here? no dependency and a warning if neither
> is available?

What would be the reason for not wanting dbus on a systemd-based system
(honest question) ?

Should we move that select to a (existing?) sub-option of systemd?

> adding some BR2_HAS_DBUS_DAEMON that is set by both, so systemd
> features (like logind) and packages depending on that (and potentially
> on PACKAGE_DBUS if they need the library or tools)?
> (https://github.com/nolange/buildroot/commits/improve_systemd_nodbus)

In the current case, we would have the systemd's sub-option(s) select
what they require, and move the select down to logind (and other
sub-options, maybe?)

        bool "logind"
        depends on BR2_USE_MMU  # dbus && dbus-broker
        depends on BR2_TOOLCHAIN_HAS_THREADS  # dbus && dbus-broker

    comment "logind needs a toolchain w/ threads"
        depends on BR2_USE_MMU
        depends on !BR2_TOOLCHAIN_HAS_THREADS

... and keep the systemd.mk as it is now.

Note that is there are three or more sub-option that require dbus, we
could go with an intermediate option:

        depends on BR2_USE_MMU  # dbus && dbus-broker
        depends on BR2_TOOLCHAIN_HAS_THREADS  # dbus && dbus-broker

        bool "logind"
        depends on BR2_USE_MMU  # needs_dbus
        depends on BR2_TOOLCHAIN_HAS_THREADS  # needs_dbus

    comment "logind needs a toolchain w/ threads"
        depends on BR2_USE_MMU
        depends on !BR2_TOOLCHAIN_HAS_THREADS

> >   - a runtime test that demonstrates that systemd does run fine with
> >     dbus-broker, and that the original dbus still takes precendence when
> >     both dbus and dbus-broker are enabled.
> >
> > Note that the runtime test is not only about demonstrating the feature;
> > it is also and foremost a way to guarantee that any regression will be
> > caught, since we automatically run the runtime tests weekly in gitlab-ci.
> Ok. Since you already have that, and I know little about your test framework,
> then could you please incorporate this version into your patch-set.

If you agree, then I'll try to merge your new submission with your
comments into my series and re-spin it soon-ish, if that's OK with you.

Yann E. MORIN.

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