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    SubjectRe: [PATCH 2/2] cgroup: add xattr support
    Hello,

    On Mon, Jan 16, 2012 at 04:07:05PM +0800, Li Zefan wrote:
    > 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
    >
    > Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>

    Ummm... I don't feel too good about this. Why can't those extra
    information be kept somewhere else? Overloading cgroupfs as storage
    for essentially opaque userland information doesn't seem like a good
    idea to me.

    Thanks.

    --
    tejun


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