cgroup: add documentation on extended attributes usage

v2: update cgroups.txt instead of creating a new file

Cc: Tejun Heo <tj@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Hillf Danton <dhillf@gmail.com>
Cc: Lennart Poettering <lpoetter@redhat.com>
Acked-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Aristeu Rozanski <aris@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Aristeu Rozanski 2012-09-11 16:28:10 -04:00 committed by Tejun Heo
parent a1a71b45a6
commit 19ec2567e0

View File

@ -29,7 +29,8 @@ CONTENTS:
3.1 Overview
3.2 Synchronization
3.3 Subsystem API
4. Questions
4. Extended attributes usage
5. Questions
1. Control Groups
=================
@ -650,7 +651,26 @@ and root cgroup. Currently this will only involve movement between
the default hierarchy (which never has sub-cgroups) and a hierarchy
that is being created/destroyed (and hence has no sub-cgroups).
4. Questions
4. Extended attribute usage
===========================
cgroup filesystem supports certain types of extended attributes in its
directories and files. The current supported types are:
- Trusted (XATTR_TRUSTED)
- Security (XATTR_SECURITY)
Both require CAP_SYS_ADMIN capability to set.
Like in tmpfs, the extended attributes in cgroup filesystem are stored
using kernel memory and it's advised to keep the usage at minimum. This
is the reason why user defined extended attributes are not supported, since
any user can do it and there's no limit in the value size.
The current known users for this feature are SELinux to limit cgroup usage
in containers and systemd for assorted meta data like main PID in a cgroup
(systemd creates a cgroup per service).
5. Questions
============
Q: what's up with this '/bin/echo' ?