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Subject[PATCH 09/10] cgroup: introduce struct cfent
Date
This patch adds cfent (cgroup file entry) which is the association
between a cgroup and a file. This is in-cgroup representation of
files under a cgroup directory. This simplifies walking walking
cgroup files and thus cgroup_clear_directory(), which is now
implemented in two parts - cgroup_rm_file() and a loop around it.

cgroup_rm_file() will be used to implement cftype removal and cfent is
scheduled to serve cgroup specific per-file data (e.g. for sysfs-like
"sever" semantics).

Signed-off-by: Tejun Heo <tj@kernel.org>
---
include/linux/cgroup.h | 1 +
kernel/cgroup.c | 107 ++++++++++++++++++++++++++++++++----------------
2 files changed, 72 insertions(+), 36 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 05ddf59..caeaafc 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -175,6 +175,7 @@ struct cgroup {
*/
struct list_head sibling; /* my parent's children */
struct list_head children; /* my children */
+ struct list_head files; /* my files */

struct cgroup *parent; /* my parent */
struct dentry __rcu *dentry; /* cgroup fs entry, RCU protected */
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 765d9f5..c0c61b9 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -158,6 +158,15 @@ struct cftype_set {
};

/*
+ * cgroupfs file entry, pointed to from leaf dentry->d_fsdata.
+ */
+struct cfent {
+ struct list_head node;
+ struct dentry *dentry;
+ struct cftype *type;
+};
+
+/*
* CSS ID -- ID per subsys's Cgroup Subsys State(CSS). used only when
* cgroup_subsys->use_id != 0.
*/
@@ -297,11 +306,16 @@ static inline struct cgroup *__d_cgrp(struct dentry *dentry)
return dentry->d_fsdata;
}

-static inline struct cftype *__d_cft(struct dentry *dentry)
+static inline struct cfent *__d_cfe(struct dentry *dentry)
{
return dentry->d_fsdata;
}

+static inline struct cftype *__d_cft(struct dentry *dentry)
+{
+ return __d_cfe(dentry)->type;
+}
+
/* the list of cgroups eligible for automatic release. Protected by
* release_list_lock */
static LIST_HEAD(release_list);
@@ -905,34 +919,38 @@ static void remove_dir(struct dentry *d)
dput(parent);
}

-static void cgroup_clear_directory(struct dentry *dentry)
-{
- struct list_head *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);
-
- spin_lock_nested(&d->d_lock, DENTRY_D_LOCK_NESTED);
- list_del_init(node);
- 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);
- 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;
+static int cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
+{
+ struct cfent *cfe;
+
+ lockdep_assert_held(&cgrp->dentry->d_inode->i_mutex);
+ lockdep_assert_held(&cgroup_mutex);
+
+ list_for_each_entry(cfe, &cgrp->files, node) {
+ struct dentry *d = cfe->dentry;
+
+ if (cft && cfe->type != cft)
+ continue;
+
+ dget(d);
+ d_delete(d);
+ simple_unlink(d->d_inode, d);
+ dput(d);
+
+ list_del_init(&cfe->node);
+ kfree(cfe);
+ return 0;
}
- spin_unlock(&dentry->d_lock);
+ return -ENOENT;
+}
+
+static void cgroup_clear_directory(struct dentry *dir)
+{
+ struct cgroup *cgrp = __d_cgrp(dir);
+
+ while (!list_empty(&cgrp->files))
+ cgroup_rm_file(cgrp, NULL);
+ WARN_ON_ONCE(!list_empty(&dir->d_subdirs));
}

/*
@@ -1362,6 +1380,7 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
{
INIT_LIST_HEAD(&cgrp->sibling);
INIT_LIST_HEAD(&cgrp->children);
+ INIT_LIST_HEAD(&cgrp->files);
INIT_LIST_HEAD(&cgrp->css_sets);
INIT_LIST_HEAD(&cgrp->release_list);
INIT_LIST_HEAD(&cgrp->pidlists);
@@ -2633,7 +2652,9 @@ static int cgroup_add_file(struct cgroup *cgrp, struct cgroup_subsys *subsys,
const struct cftype *cft)
{
struct dentry *dir = cgrp->dentry;
+ struct cgroup *parent = __d_cgrp(dir);
struct dentry *dentry;
+ struct cfent *cfe;
int error;
umode_t mode;
char name[MAX_CGROUP_TYPE_NAMELEN + MAX_CFTYPE_NAME + 2] = { 0 };
@@ -2649,17 +2670,31 @@ static int cgroup_add_file(struct cgroup *cgrp, struct cgroup_subsys *subsys,
strcat(name, ".");
}
strcat(name, cft->name);
+
BUG_ON(!mutex_is_locked(&dir->d_inode->i_mutex));
+
+ cfe = kzalloc(sizeof(*cfe), GFP_KERNEL);
+ if (!cfe)
+ return -ENOMEM;
+
dentry = lookup_one_len(name, dir, strlen(name));
- if (!IS_ERR(dentry)) {
- mode = cgroup_file_mode(cft);
- error = cgroup_create_file(dentry, mode | S_IFREG,
- cgrp->root->sb);
- if (!error)
- dentry->d_fsdata = (void *)cft;
- dput(dentry);
- } else
+ if (IS_ERR(dentry)) {
error = PTR_ERR(dentry);
+ goto out;
+ }
+
+ mode = cgroup_file_mode(cft);
+ error = cgroup_create_file(dentry, mode | S_IFREG, cgrp->root->sb);
+ if (!error) {
+ cfe->type = (void *)cft;
+ cfe->dentry = dentry;
+ dentry->d_fsdata = cfe;
+ list_add_tail(&cfe->node, &parent->files);
+ cfe = NULL;
+ }
+ dput(dentry);
+out:
+ kfree(cfe);
return error;
}

--
1.7.7.3


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