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authorAristeu Rozanski <aris@redhat.com>2012-09-11 16:28:10 -0400
committerTejun Heo <tj@kernel.org>2012-09-12 11:39:50 -0700
commit19ec2567e0a5fe64f4404ad6df697894aec8c493 (patch)
tree64424d60857c7ec9192e4113643071a2a727c7cb /Documentation/cgroups
parenta1a71b45a66fd3c3c453b55fbd180f8fccdd1daa (diff)
downloadlinux-19ec2567e0a5fe64f4404ad6df697894aec8c493.tar.gz
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>
Diffstat (limited to 'Documentation/cgroups')
-rw-r--r--Documentation/cgroups/cgroups.txt24
1 files changed, 22 insertions, 2 deletions
diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
index 4a0b64c605f..004fd5a09e1 100644
--- a/Documentation/cgroups/cgroups.txt
+++ b/Documentation/cgroups/cgroups.txt
@@ -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' ?