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Subject[PATCH v6 2/4] cgroup: revise how we re-populate root directory
From: Li Zefan <lizefan@huawei.com>

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 unbinded, 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.

v6:
- no changes
v5:
- no changes
v4:
- refactored cgroup_clear_directory() to not use cgroup_rm_file()
- instead of going thru the list of files, get the file list using the
subsystems
- use 'subsys_mask' instead of {added,removed}_bits and made
cgroup_populate_dir() to match the parameters with cgroup_clear_directory()
v3:
- refresh patches after recent refactoring
Cc: Li Zefan <lizefan@huawei.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Hillf Danton <dhillf@gmail.com>
Cc: Lennart Poettering <lpoetter@redhat.com>
Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Aristeu Rozanski <aris@redhat.com>

---
kernel/cgroup.c | 61 ++++++++++++++++++++++++++++++++++++++++++++------------
1 file changed, 48 insertions(+), 13 deletions(-)
Index: github/kernel/cgroup.c
===================================================================
--- github.orig/kernel/cgroup.c 2012-08-16 11:28:12.683272452 -0400
+++ github/kernel/cgroup.c 2012-08-16 11:28:42.592089681 -0400
@@ -824,7 +824,8 @@
static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode);
static struct dentry *cgroup_lookup(struct inode *, struct dentry *, unsigned int);
static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry);
-static int cgroup_populate_dir(struct cgroup *cgrp);
+static int cgroup_populate_dir(struct cgroup *cgrp, bool base_files,
+ unsigned long subsys_mask);
static const struct inode_operations cgroup_dir_inode_operations;
static const struct file_operations proc_cgroupstats_operations;

@@ -963,12 +964,29 @@
return -ENOENT;
}

-static void cgroup_clear_directory(struct dentry *dir)
+/**
+ * cgroup_clear_directory - selective removal of base and subsystem files
+ * @dir: directory containing the files
+ * @base_files: true if the base files should be removed
+ * @subsys_mask: mask of the subsystem ids whose files should be removed
+ */
+static void cgroup_clear_directory(struct dentry *dir, bool base_files,
+ unsigned long subsys_mask)
{
struct cgroup *cgrp = __d_cgrp(dir);
+ struct cgroup_subsys *ss;

- while (!list_empty(&cgrp->files))
- cgroup_rm_file(cgrp, NULL);
+ for_each_subsys(cgrp->root, ss) {
+ struct cftype_set *set;
+ if (!test_bit(ss->subsys_id, &subsys_mask))
+ continue;
+ list_for_each_entry(set, &ss->cftsets, node)
+ cgroup_rm_file(cgrp, set->cfts);
+ }
+ if (base_files) {
+ while (!list_empty(&cgrp->files))
+ cgroup_rm_file(cgrp, NULL);
+ }
}

/*
@@ -977,8 +995,9 @@
static void cgroup_d_remove_dir(struct dentry *dentry)
{
struct dentry *parent;
+ struct cgroupfs_root *root = dentry->d_sb->s_fs_info;

- cgroup_clear_directory(dentry);
+ cgroup_clear_directory(dentry, true, root->subsys_bits);

parent = dentry->d_parent;
spin_lock(&parent->d_lock);
@@ -1339,6 +1358,7 @@
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);
@@ -1354,6 +1374,9 @@
pr_warning("cgroup: option changes via remount are deprecated (pid=%d comm=%s)\n",
task_tgid_nr(current), current->comm);

+ 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))) {
@@ -1369,8 +1392,9 @@
}

/* clear out any existing files and repopulate subsystem files */
- cgroup_clear_directory(cgrp->dentry);
- cgroup_populate_dir(cgrp);
+ cgroup_clear_directory(cgrp->dentry, false, removed_bits);
+ /* re-populate subsystem files */
+ cgroup_populate_dir(cgrp, false, added_bits);

if (opts.release_agent)
strcpy(root->release_agent_path, opts.release_agent);
@@ -1669,7 +1693,7 @@
BUG_ON(root->number_of_cgroups != 1);

cred = override_creds(&init_cred);
- cgroup_populate_dir(root_cgrp);
+ cgroup_populate_dir(root_cgrp, true, root->subsys_bits);
revert_creds(cred);
mutex_unlock(&cgroup_root_mutex);
mutex_unlock(&cgroup_mutex);
@@ -3843,18 +3867,29 @@
{ } /* terminate */
};

-static int cgroup_populate_dir(struct cgroup *cgrp)
+/**
+ * cgroup_populate_dir - selectively creation of files in a directory
+ * @cgrp: target cgroup
+ * @base_files: true if the base files should be added
+ * @subsys_mask: mask of the subsystem ids whose files should be added
+ */
+static int cgroup_populate_dir(struct cgroup *cgrp, bool base_files,
+ unsigned long subsys_mask)
{
int err;
struct cgroup_subsys *ss;

- err = cgroup_addrm_files(cgrp, NULL, files, true);
- if (err < 0)
- return err;
+ if (base_files) {
+ err = cgroup_addrm_files(cgrp, NULL, files, true);
+ if (err < 0)
+ return err;
+ }

/* process cftsets of each subsystem */
for_each_subsys(cgrp->root, ss) {
struct cftype_set *set;
+ if (!test_bit(ss->subsys_id, &subsys_mask))
+ continue;

list_for_each_entry(set, &ss->cftsets, node)
cgroup_addrm_files(cgrp, ss, set->cfts, true);
@@ -3988,7 +4023,7 @@

list_add_tail(&cgrp->allcg_node, &root->allcg_list);

- err = cgroup_populate_dir(cgrp);
+ err = cgroup_populate_dir(cgrp, true, root->subsys_bits);
/* If err < 0, we have a half-filled directory - oh well ;) */

mutex_unlock(&cgroup_mutex);


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