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Subject[PATCH 1/2] cgroup: revise how we re-populate root directory
When remounting cgroupfs with some subsystems added to it and some
removed, cgroup will remove all the files in root directory and then
re-popluate it.

What I'm doing here is, only remove files which belong to subsystems that
are to be unbound, and only create files for newly-added subsystems.
The purpose is to have all other files untouched.

This is a preparation for cgroup xattr support.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
include/linux/cgroup.h | 11 +++---
kernel/cgroup.c | 92 +++++++++++++++++++++++++++++++----------------
2 files changed, 67 insertions(+), 36 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index e9b6021..13db9e8 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -327,6 +327,9 @@ struct cftype {
*/
size_t max_write_len;

+ /* The subsystem this cgroup file belongs to */
+ struct cgroup_subsys *subsys;
+
int (*open)(struct inode *inode, struct file *file);
ssize_t (*read)(struct cgroup *cgrp, struct cftype *cft,
struct file *file,
@@ -419,16 +422,14 @@ struct cgroup_scanner {
* called by subsystems from within a populate() method
*/
int cgroup_add_file(struct cgroup *cgrp, struct cgroup_subsys *subsys,
- const struct cftype *cft);
+ struct cftype *cft);

/*
* Add a set of new files to the given cgroup directory. Should
* only be called by subsystems from within a populate() method
*/
-int cgroup_add_files(struct cgroup *cgrp,
- struct cgroup_subsys *subsys,
- const struct cftype cft[],
- int count);
+int cgroup_add_files(struct cgroup *cgrp, struct cgroup_subsys *subsys,
+ struct cftype cft[], int count);

int cgroup_is_removed(const struct cgroup *cgrp);

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index a5d3b53..c4ed6fe 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -781,6 +781,8 @@ static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode);
static struct dentry *cgroup_lookup(struct inode *, struct dentry *, struct nameidata *);
static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry);
static int cgroup_populate_dir(struct cgroup *cgrp);
+static int cgroup_repopulate_dir(struct cgroup *cgrp, unsigned long added_bits,
+ unsigned long removed_bits);
static const struct inode_operations cgroup_dir_inode_operations;
static const struct file_operations proc_cgroupstats_operations;

@@ -882,34 +884,44 @@ static void remove_dir(struct dentry *d)
dput(parent);
}

-static void cgroup_clear_directory(struct dentry *dentry)
+static void cgroup_clear_directory(struct dentry *dentry, bool remove_all,
+ unsigned long removed_bits)
{
- struct list_head *node;
+ LIST_HEAD(head);
+ struct dentry *d, *node;

BUG_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
+
spin_lock(&dentry->d_lock);
- node = dentry->d_subdirs.next;
- while (node != &dentry->d_subdirs) {
- struct dentry *d = list_entry(node, struct dentry, d_u.d_child);
+ list_for_each_entry_safe(d, node, &dentry->d_subdirs, d_u.d_child) {
+ struct cftype *cft = d->d_fsdata;
+
+ if (!remove_all && cft->subsys &&
+ !test_bit(cft->subsys->subsys_id, &removed_bits))
+ continue;

spin_lock_nested(&d->d_lock, DENTRY_D_LOCK_NESTED);
- list_del_init(node);
+ list_move(&d->d_u.d_child, &head);
if (d->d_inode) {
/* This should never be called on a cgroup
* directory with child cgroups */
BUG_ON(d->d_inode->i_mode & S_IFDIR);
dget_dlock(d);
- spin_unlock(&d->d_lock);
- spin_unlock(&dentry->d_lock);
+ }
+ spin_unlock(&d->d_lock);
+ }
+ spin_unlock(&dentry->d_lock);
+
+ list_for_each_entry_safe(d, node, &head, d_u.d_child) {
+ spin_lock(&d->d_lock);
+ list_del_init(&d->d_u.d_child);
+ spin_unlock(&d->d_lock);
+ if (d->d_inode) {
d_delete(d);
simple_unlink(dentry->d_inode, d);
dput(d);
- spin_lock(&dentry->d_lock);
- } else
- spin_unlock(&d->d_lock);
- node = dentry->d_subdirs.next;
+ }
}
- spin_unlock(&dentry->d_lock);
}

/*
@@ -919,7 +931,7 @@ static void cgroup_d_remove_dir(struct dentry *dentry)
{
struct dentry *parent;

- cgroup_clear_directory(dentry);
+ cgroup_clear_directory(dentry, true, 0);

parent = dentry->d_parent;
spin_lock(&parent->d_lock);
@@ -1284,6 +1296,7 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
struct cgroupfs_root *root = sb->s_fs_info;
struct cgroup *cgrp = &root->top_cgroup;
struct cgroup_sb_opts opts;
+ unsigned long added_bits, removed_bits;

mutex_lock(&cgrp->dentry->d_inode->i_mutex);
mutex_lock(&cgroup_mutex);
@@ -1294,6 +1307,9 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
if (ret)
goto out_unlock;

+ added_bits = opts.subsys_bits & ~root->subsys_bits;
+ removed_bits = root->subsys_bits & ~opts.subsys_bits;
+
/* Don't allow flags or name to change at remount */
if (opts.flags != root->flags ||
(opts.name && strcmp(opts.name, root->name))) {
@@ -1308,8 +1324,8 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
goto out_unlock;
}

- /* (re)populate subsystem files */
- cgroup_populate_dir(cgrp);
+ /* re-populate subsystem files */
+ cgroup_repopulate_dir(cgrp, added_bits, removed_bits);

if (opts.release_agent)
strcpy(root->release_agent_path, opts.release_agent);
@@ -2710,16 +2726,17 @@ static umode_t cgroup_file_mode(const struct cftype *cft)
return mode;
}

-int cgroup_add_file(struct cgroup *cgrp,
- struct cgroup_subsys *subsys,
- const struct cftype *cft)
+int cgroup_add_file(struct cgroup *cgrp, struct cgroup_subsys *subsys,
+ struct cftype *cft)
{
struct dentry *dir = cgrp->dentry;
struct dentry *dentry;
int error;
umode_t mode;
-
char name[MAX_CGROUP_TYPE_NAMELEN + MAX_CFTYPE_NAME + 2] = { 0 };
+
+ cft->subsys = subsys;
+
if (subsys && !test_bit(ROOT_NOPREFIX, &cgrp->root->flags)) {
strcpy(name, subsys->name);
strcat(name, ".");
@@ -2740,10 +2757,8 @@ int cgroup_add_file(struct cgroup *cgrp,
}
EXPORT_SYMBOL_GPL(cgroup_add_file);

-int cgroup_add_files(struct cgroup *cgrp,
- struct cgroup_subsys *subsys,
- const struct cftype cft[],
- int count)
+int cgroup_add_files(struct cgroup *cgrp, struct cgroup_subsys *subsys,
+ struct cftype cft[], int count)
{
int i, err;
for (i = 0; i < count; i++) {
@@ -3703,26 +3718,27 @@ static struct cftype cft_release_agent = {
.max_write_len = PATH_MAX,
};

-static int cgroup_populate_dir(struct cgroup *cgrp)
+static int __cgroup_populate_dir(struct cgroup *cgrp, unsigned long added_bits)
{
int err;
struct cgroup_subsys *ss;

- /* First clear out any existing files */
- cgroup_clear_directory(cgrp->dentry);
-
err = cgroup_add_files(cgrp, NULL, files, ARRAY_SIZE(files));
if (err < 0)
return err;

if (cgrp == cgrp->top_cgroup) {
- if ((err = cgroup_add_file(cgrp, NULL, &cft_release_agent)) < 0)
+ err = cgroup_add_file(cgrp, NULL, &cft_release_agent);
+ if (err < 0)
return err;
}

for_each_subsys(cgrp->root, ss) {
- if (ss->populate && (err = ss->populate(ss, cgrp)) < 0)
- return err;
+ if (test_bit(ss->subsys_id, &added_bits) && ss->populate) {
+ err = ss->populate(ss, cgrp);
+ if (err < 0)
+ return err;
+ }
}
/* This cgroup is ready now */
for_each_subsys(cgrp->root, ss) {
@@ -3739,6 +3755,20 @@ static int cgroup_populate_dir(struct cgroup *cgrp)
return 0;
}

+static int cgroup_populate_dir(struct cgroup *cgrp)
+{
+ return __cgroup_populate_dir(cgrp, cgrp->root->subsys_bits);
+}
+
+static int cgroup_repopulate_dir(struct cgroup *cgrp, unsigned long added_bits,
+ unsigned long removed_bits)
+{
+ /* First clear out files */
+ cgroup_clear_directory(cgrp->dentry, false, removed_bits);
+
+ return __cgroup_populate_dir(cgrp, added_bits);
+}
+
static void init_cgroup_css(struct cgroup_subsys_state *css,
struct cgroup_subsys *ss,
struct cgroup *cgrp)
--
1.7.3.1

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