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authorSerge E. Hallyn <serue@us.ibm.com>2008-12-08 15:52:21 -0600
committerJames Morris <jmorris@namei.org>2008-12-09 09:25:53 +1100
commit94d6a5f7341ebaff53d4e41cc81fab37f0d9fbed (patch)
tree07b4a016a50f1cc42c6295ec387a26d1a4481381
parent7657d90497f98426af17f0ac633a9b335bb7a8fb (diff)
downloadlinux-2.6.38-lt-ux500-94d6a5f7341ebaff53d4e41cc81fab37f0d9fbed.tar.gz
user namespaces: document CFS behavior
Documented the currently bogus state of support for CFS user groups with user namespaces. In particular, all users in a user namespace should be children of the user which created the user namespace. This is yet to be implemented. Signed-off-by: Serge E. Hallyn <serue@us.ibm.com> Acked-by: Dhaval Giani <dhaval@linux.vnet.ibm.com> Signed-off-by: Serge E. Hallyn <serue@us.ibm.com> Signed-off-by: James Morris <jmorris@namei.org>
-rw-r--r--Documentation/scheduler/sched-design-CFS.txt21
-rw-r--r--kernel/user.c8
2 files changed, 28 insertions, 1 deletions
diff --git a/Documentation/scheduler/sched-design-CFS.txt b/Documentation/scheduler/sched-design-CFS.txt
index eb471c7a905..8398ca4ff4e 100644
--- a/Documentation/scheduler/sched-design-CFS.txt
+++ b/Documentation/scheduler/sched-design-CFS.txt
@@ -273,3 +273,24 @@ task groups and modify their CPU share using the "cgroups" pseudo filesystem.
# #Launch gmplayer (or your favourite movie player)
# echo <movie_player_pid> > multimedia/tasks
+
+8. Implementation note: user namespaces
+
+User namespaces are intended to be hierarchical. But they are currently
+only partially implemented. Each of those has ramifications for CFS.
+
+First, since user namespaces are hierarchical, the /sys/kernel/uids
+presentation is inadequate. Eventually we will likely want to use sysfs
+tagging to provide private views of /sys/kernel/uids within each user
+namespace.
+
+Second, the hierarchical nature is intended to support completely
+unprivileged use of user namespaces. So if using user groups, then
+we want the users in a user namespace to be children of the user
+who created it.
+
+That is currently unimplemented. So instead, every user in a new
+user namespace will receive 1024 shares just like any user in the
+initial user namespace. Note that at the moment creation of a new
+user namespace requires each of CAP_SYS_ADMIN, CAP_SETUID, and
+CAP_SETGID.
diff --git a/kernel/user.c b/kernel/user.c
index 6c924bc48c0..6608a3d8ca6 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -239,7 +239,13 @@ static struct kobj_type uids_ktype = {
.release = uids_release,
};
-/* create /sys/kernel/uids/<uid>/cpu_share file for this user */
+/*
+ * Create /sys/kernel/uids/<uid>/cpu_share file for this user
+ * We do not create this file for users in a user namespace (until
+ * sysfs tagging is implemented).
+ *
+ * See Documentation/scheduler/sched-design-CFS.txt for ramifications.
+ */
static int uids_user_create(struct user_struct *up)
{
struct kobject *kobj = &up->kobj;