This can be used to attach metadata to a cgroup, which is required by systemd. As lazy as I am, here just quoted from Lennart for the detailed 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 Changelog v1->v2: - add kmem_xattr APIs - use these new APIs in both tmpfs and cgroup Early discussions can be found in this thread: https://lkml.org/lkml/2012/1/16/51 Note: this patchset is based on Tejun's cgroup.git/for-next -- fs/xattr.c | 167 +++++++++++++++++++++++++++++++++++++++++ include/linux/cgroup.h | 18 +++- include/linux/shmem_fs.h | 3 +- include/linux/xattr.h | 23 ++++++ init/Kconfig | 12 +++ kernel/cgroup.c | 184 ++++++++++++++++++++++++++++++++++++---------- mm/shmem.c | 151 +++----------------------------------- 7 files changed, 371 insertions(+), 187 deletions(-) -- 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
