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    Subject[PATCH v2 0/3] cgroup: add xattr support
    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(-)


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