From 94d6a5f7341ebaff53d4e41cc81fab37f0d9fbed Mon Sep 17 00:00:00 2001 From: "Serge E. Hallyn" Date: Mon, 8 Dec 2008 15:52:21 -0600 Subject: [PATCH] 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 Acked-by: Dhaval Giani Signed-off-by: Serge E. Hallyn Signed-off-by: James Morris --- Documentation/scheduler/sched-design-CFS.txt | 21 ++++++++++++++++++++ kernel/user.c | 8 +++++++- 2 files changed, 28 insertions(+), 1 deletion(-) 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 > 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//cpu_share file for this user */ +/* + * Create /sys/kernel/uids//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; -- 2.41.1