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Subject[PATCH 6/7] support checking of subsystem dependencies
From: Li Zefan <lizf@cn.fujitsu.com>

This allows one subsystem to require that it only be mounted when some
other subsystems are also present in or not in the proposed hierarchy.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
Documentation/cgroups/cgroups.txt | 5 +++++
include/linux/cgroup.h | 2 ++
kernel/cgroup.c | 21 ++++++++++++++++++++-
3 files changed, 27 insertions(+), 1 deletions(-)

diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
index d9014aa..df648c6 100644
--- a/Documentation/cgroups/cgroups.txt
+++ b/Documentation/cgroups/cgroups.txt
@@ -534,6 +534,11 @@ and root cgroup. Currently this will only involve movement between
the default hierarchy (which never has sub-cgroups) and a hierarchy
that is being created/destroyed (and hence has no sub-cgroups).

+int subsys_depend(struct cgroup_subsys *ss, unsigned long subsys_bits)
+Called when a cgroup subsystem wants to check if some other subsystems
+are also present in the proposed hierarchy. If this method returns error,
+the mount of the cgroup filesystem will fail.
+
4. Questions
============

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 1164963..1899449 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -329,6 +329,8 @@ struct cgroup_subsys {
struct cgroup *cgrp);
void (*post_clone)(struct cgroup_subsys *ss, struct cgroup *cgrp);
void (*bind)(struct cgroup_subsys *ss, struct cgroup *root);
+ int (*subsys_depend)(struct cgroup_subsys *ss,
+ unsigned long subsys_bits);
/*
* This routine is called with the task_lock of mm->owner held
*/
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index a512a75..8a07023 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -761,6 +761,25 @@ static int cgroup_show_options(struct seq_file *seq, struct vfsmount *vfs)
return 0;
}

+static int check_subsys_dependency(unsigned long subsys_bits)
+{
+ int i;
+ int ret;
+ struct cgroup_subsys *ss;
+
+ for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+ ss = subsys[i];
+
+ if (test_bit(i, &subsys_bits) && ss->subsys_depend) {
+ ret = ss->subsys_depend(ss, subsys_bits);
+ if (ret)
+ return ret;
+ }
+ }
+
+ return 0;
+}
+
struct cgroup_sb_opts {
unsigned long subsys_bits;
unsigned long flags;
@@ -821,7 +840,7 @@ static int parse_cgroupfs_options(char *data,
if (!opts->subsys_bits)
return -EINVAL;

- return 0;
+ return check_subsys_dependency(opts->subsys_bits);
}

static int cgroup_remount(struct super_block *sb, int *flags, char *data)
-- 1.5.4.rc3




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