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    Subject[PATCH v2 0/4] Support user xattrs in cgroupfs
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    User extended attributes are useful as metadata storage for kernfs
    consumers like cgroups. Especially in the case of cgroups, it is useful
    to have a central metadata store that multiple processes/services can
    use to coordinate actions.

    A concrete example is for userspace out of memory killers. We want to
    let delegated cgroup subtree owners (running as non-root) to be able to
    say "please avoid killing this cgroup". This is especially important for
    desktop linux as delegated subtrees owners are less likely to run as
    root.

    The first two commits set up some stuff for the third commit which
    intro introduce a new flag, KERNFS_ROOT_SUPPORT_USER_XATTR,
    that lets kernfs consumers enable user xattr support. The final commit
    turns on user xattr support for cgroupfs.

    Changes from v1:
    - use kvmalloc for xattr values
    - modify simple_xattr_set to return removed size
    - add accounting for total user xattr size per cgroup

    Daniel Xu (4):
    kernfs: kvmalloc xattr value instead of kmalloc
    kernfs: Add removed_size out param for simple_xattr_set
    kernfs: Add option to enable user xattrs
    cgroupfs: Support user xattrs

    fs/kernfs/inode.c | 91 ++++++++++++++++++++++++++++++++++++-
    fs/kernfs/kernfs-internal.h | 2 +
    fs/xattr.c | 17 +++++--
    include/linux/kernfs.h | 11 ++++-
    include/linux/xattr.h | 3 +-
    kernel/cgroup/cgroup.c | 3 +-
    mm/shmem.c | 2 +-
    7 files changed, 119 insertions(+), 10 deletions(-)

    --
    2.21.1

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