Le 01/02/2017 à 13:05, Gustavo Niemeyer a écrit : > > Yes, that's in the plans for configuration support already. The idea > is to extend snapctl with the ability to introspect exactly which > settings have changed since the last successful run of the script, and > perhaps which values it used to hold before. > > For the time being, I suggest not worrying much about that. Just go > ahead and implement the semantics you want the user of the snap to > experience. Inside the configure hook, check to see if the requested > value is already in place and do nothing in that case. This makes the > script idempotent, resilient because it ensures the desired state is > indeed in place, and also cheap to execute in the common case. >
If someone is interested, I have implemented this kind of idempotent configure hook example. It can be found at https://github.com/ubuntu/snow-on-me-snap/blob/master/meta/hooks/configure as part of the christmas snap demo. It features: - support key=value formatting - ignoring, but not erasing unknown keys, comment lines, empty ones. - preserving formatting and ordering, even when changing an existing key. - only snap set arguments will be modified if a value is set. If the value assigned to it is empty, removing the key line - new elements not present in existing configuration file are simply appended. Supporting new keys (like here "foo") is just a matter of adding: update_opt_in_config foo at the end of the file. I hope this helps! (note that the issue is still "what's the supported keys for this snap?") Cheers, Didier > > > On Wed, Feb 1, 2017 at 8:31 AM, Oliver Grawert <o...@ubuntu.com > <mailto:o...@ubuntu.com>> wrote: > > hi, > > after we recently added a config hook [1] to the core snap it is now > possible to disable ssh if you require [2] ... > > there is a long standing request to do the same for syslog for systems > running from SD card, which is why i looked into trying to extend the > existing configure script for this, which made me notice some issue... > > when you call "snap set core foo=bar", there is no indication at all > for the script which variable changes a value, neither in the shell > environment nor in the argument list. > > the only way to get your value is to call snapctl for every existing > variable [3]. since you dont know what specific variable was requested > to change the only way to reliably write it is to write *all* existing > variables ... > > now, if you package something with a more complex config that you want > completely handled via snap config this gets ugly very fast... imagine > something like postfix with can potentially have 100s of config > options. instead of atomically changing a single option you will > regenerate the full config from scratch. this takes a lot longer, > bringing the risk of a completely broken config in case of a power > loss, beyond resulting an an awful config hook script with a large > block of "snapctl get" calls at the top. > > can we extend the config hook implementation minimally so a "snap set > core foo=bar" would at least have something like "SNAP_OPTION=foo" in > the environment that the generating script or binary could read to > avoid the unnecessary processing or would that break some design > concept ? > > ciao > oli > > [1] http://bazaar.launchpad.net/~snappy-dev/core-snap/trunk/view/head:/ > hooks/configure > > <http://bazaar.launchpad.net/%7Esnappy-dev/core-snap/trunk/view/head:/%0Ahooks/configure> > [2] https://github.com/CanonicalLtd/ubuntu-core-docs/blob/master/en/ref > erence/core-configuration.md > > <https://github.com/CanonicalLtd/ubuntu-core-docs/blob/master/en/ref%0Aerence/core-configuration.md> > [3] https://github.com/snapcore/snapd/wiki/hooks > <https://github.com/snapcore/snapd/wiki/hooks> > -- > Snapcraft mailing list > Snapcraft@lists.snapcraft.io <mailto:Snapcraft@lists.snapcraft.io> > Modify settings or unsubscribe at: > https://lists.ubuntu.com/mailman/listinfo/snapcraft > <https://lists.ubuntu.com/mailman/listinfo/snapcraft> > > > > > -- > gustavo @ http://niemeyer.net > >
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