On Thu, Aug 16, 2012 at 01:44:56PM -0400, aris@xxxxxxxxxx wrote: > From: Li Zefan <lizefan@xxxxxxxxxx> > > This is one of the items in the plumber's wish list. > > For use cases: > > >> What would the use case be for this? > > > > 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. > > > > Lennart > > v6: > - remove user xattr namespace, only allow trusted and security > v5: > - check for capabilities before setting/removing xattrs > v4: > - no changes > v3: > - instead of config option, use mount option to enable xattr support > > Cc: Li Zefan <lizefan@xxxxxxxxxx> > Cc: Tejun Heo <tj@xxxxxxxxxx> > Cc: Hugh Dickins <hughd@xxxxxxxxxx> > Cc: Hillf Danton <dhillf@xxxxxxxxx> > Cc: Lennart Poettering <lpoetter@xxxxxxxxxx> > Signed-off-by: Li Zefan <lizefan@xxxxxxxxxx> > Signed-off-by: Aristeu Rozanski <aris@xxxxxxxxxx> 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? Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
