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Subject[PATCH] cgroup: deprecate remount option changes mount option
This patch marks the following features for deprecation.

* Rebinding subsys by remount: Never reached useful state - only works
on empty hierarchies.

* release_agent update by remount: release_agent itself will be
replaced with conventional fsnotify notification.

v2: Lennart pointed out that "name=" is necessary for mounts w/o any
controller attached. Drop "name=" deprecation.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Lennart Poettering <mzxreary@0pointer.de>
---
Documentation/feature-removal-schedule.txt | 10 ++++++++++
kernel/cgroup.c | 5 +++++
2 files changed, 15 insertions(+)

Index: work/Documentation/feature-removal-schedule.txt
===================================================================
--- work.orig/Documentation/feature-removal-schedule.txt
+++ work/Documentation/feature-removal-schedule.txt
@@ -510,3 +510,13 @@ Why: The pci_scan_bus_parented() interfa
convert to using pci_scan_root_bus() so they can supply a list of
bus resources when the bus is created.
Who: Bjorn Helgaas <bhelgaas@google.com>
+
+----------------------------
+
+What: cgroup option updates via remount
+When: March 2013
+Why: Remount currently allows changing bound subsystems and
+ release_agent. Rebinding is hardly useful as it only works
+ when the hierarchy is empty and release_agent itself should be
+ replaced with conventional fsnotify.
+Who: Tejun Heo <tj@kernel.org>
Index: work/kernel/cgroup.c
===================================================================
--- work.orig/kernel/cgroup.c
+++ work/kernel/cgroup.c
@@ -1294,6 +1294,11 @@ static int cgroup_remount(struct super_b
if (ret)
goto out_unlock;

+ /* See feature-removal-schedule.txt */
+ if (opts.subsys_bits != root->actual_subsys_bits || opts.release_agent)
+ pr_warning("cgroup: option changes via remount are deprecated (pid=%d comm=%s)\n",
+ task_tgid_nr(current), current->comm);
+
/* Don't allow flags or name to change at remount */
if (opts.flags != root->flags ||
(opts.name && strcmp(opts.name, root->name))) {

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