Re: triggering udev rules based on the state of udevd

[Bill Nottingham <notting@redhat.com>]

Kay Sievers (kay.sievers@vrfy.org) said: 
> > There doesn't seem to be a good happy medium that allows for degraded assembly
> > when needed, but normal assembly in most cases. One potential way to do this
> > would be to queue events such as these RAID-handling events as 'idle', or
> > 'end of queue', such that they are always run at the end of queue after other
> > events have run. Is that sort of thing possible?
> 
> What would be a "queue"? How would you define one?

The event queue... basically just a push an event to 'last'.

> Can't you run a "all I need is there" - check with every matching
> device, and make sure, you serialize/lock things properly, and only
> the last device/event would have all needed requirements and trigger
> the action, all earlier would just need to give up. The s390 stuff
> does things like that with the "collect" extra, Ubuntu has a
> "watershed" extra, which may do something like you need.

watershed just locks to avoid running multiple instances of the same
base command; it doesn't actually solve this. Moreover, just saying
'only the last device/event' isn't really proper - how do you tell what
is 'last' in the event of a degraded raid array?

Bill