Heya, (sorry for the late reply)
On 16.08.2012 22:00, Tejun Heo wrote:
On Thu, Aug 16, 2012 at 01:44:56PM -0400, a...@redhat.com wrote:
Attaching meta information to services, in an easily discoverable way. For example, in systemd we create one cgroup for each service, and could then store data like the main pid of the specific service as an xattr on the cgroup itself. That way we'd have almost all service state in the cgroupfs, which would make it possible to terminate systemd and later restart it without losing any state information. But there's more: for example, some very peculiar services cannot be terminated on shutdown (i.e. fakeraid DM stuff) and it would be really nice if the services in question could just mark that on their cgroup, by setting an xattr. On the more desktopy side of things there are other possibilities: for example there are plans defining what an application is along the lines of a cgroup (i.e. an app being a collection of processes). With xattrs one could then attach an icon or human readable program name on the cgroup. The key idea is that this would allow attaching runtime meta information to cgroups and everything they model (services, apps, vms), that doesn't need any complex userspace infrastructure, has good access control (i.e. because the file system enforces that anyway, and there's the "trusted." xattr namespace), notifications (inotify), and can easily be shared among applications.
I'm not against this but unsure whether using kmem is enough for the suggested use case. Lennart, would this suit systemd? How much metadata are we talking about?
Just small things, like values, PIDs, i.e. a few 100 bytes or so per cgroup should be more than sufficient for our needs.
Lennart -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
