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Commit 94d6a5f7 authored by Serge E. Hallyn's avatar Serge E. Hallyn Committed by James Morris
Browse files

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: default avatarSerge E. Hallyn <serue@us.ibm.com>
Acked-by: default avatarDhaval Giani <dhaval@linux.vnet.ibm.com>

Signed-off-by: default avatarSerge E. Hallyn <serue@us.ibm.com>
Signed-off-by: default avatarJames Morris <jmorris@namei.org>
parent 7657d904

Documentation/scheduler/sched-design-CFS.txt

+21 −0
Original line number Original line Diff line number Diff line
@@ -273,3 +273,24 @@ task groups and modify their CPU share using the "cgroups" pseudo filesystem. 




	# #Launch gmplayer (or your favourite movie player)

	# #Launch gmplayer (or your favourite movie player)

	# echo <movie_player_pid> > multimedia/tasks

	# 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.

kernel/user.c

+7 −1
Original line number Original line Diff line number Diff line
@@ -239,7 +239,13 @@ static struct kobj_type uids_ktype = { 
	.release = uids_release,

	.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)

static int uids_user_create(struct user_struct *up)

{

{

	struct kobject *kobj = &up->kobj;

	struct kobject *kobj = &up->kobj;