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user namespaces: document CFS behavior

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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>
This commit is contained in:
Serge E. Hallyn 2008-12-08 15:52:21 -06:00 committed by James Morris
parent 7657d90497
commit 94d6a5f734
2 changed files with 28 additions and 1 deletions
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21
Documentation/scheduler/sched-design-CFS.txt
View file

@ -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.

8
kernel/user.c
View file

@ -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;