From: Aristeu Rozanski Date: Tue, 11 Sep 2012 20:28:10 +0000 (-0400) Subject: cgroup: add documentation on extended attributes usage X-Git-Tag: next-20120912~60^2~1 X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=e0cfb101de349d7c1d84eb349f2a385dbbf17350;p=karo-tx-linux.git cgroup: add documentation on extended attributes usage v2: update cgroups.txt instead of creating a new file Cc: Li Zefan Cc: Tejun Heo Cc: Hugh Dickins Cc: Hillf Danton Cc: Lennart Poettering Signed-off-by: Aristeu Rozanski Signed-off-by: Tejun Heo --- diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt index 4a0b64c605fc..004fd5a09e12 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' ?