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". In server environments this is
less important as everyone is running as root. But for desktop linux,
this is more important.
The first patch introduces a new flag, KERNFS_ROOT_SUPPORT_USER_XATTR,
that lets kernfs consumers enable user xattr support. The second patch
turns on this feature for cgroupfs.
Daniel Xu (2):
kernfs: Add option to enable user xattrs
cgroupfs: Support user xattrs
fs/kernfs/inode.c | 47 +++++++++++++++++++++++++++++++++++++
fs/kernfs/kernfs-internal.h | 1 +
include/linux/kernfs.h | 6 +++++
kernel/cgroup/cgroup.c | 3 ++-
4 files changed, 56 insertions(+), 1 deletion(-)
--
2.21.1
Hi Daniel,
On Mon, Mar 2, 2020 at 5:42 PM Daniel Xu <[email protected]> wrote:
>
> 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". In server environments this is
> less important as everyone is running as root.
I would recommend removing the "everyone is running as root" statement
as it is not generally true.
Shakeel
On Tue Mar 3, 2020 at 8:50 AM, Shakeel Butt wrote:
> Hi Daniel,
>
>
> On Mon, Mar 2, 2020 at 5:42 PM Daniel Xu <[email protected]> wrote:
> >
> > 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". In server environments this is
> > less important as everyone is running as root.
>
>
> I would recommend removing the "everyone is running as root" statement
> as it is not generally true.
>
>
> Shakeel
Good point, thanks.