aboutsummaryrefslogtreecommitdiffstats
path: root/Documentation/cgroups/cgroups.txt
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/cgroups/cgroups.txt')
-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 4a0b64c..004fd5a 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' ?