cgroup: generalize cgroup_pidlist_open_file

In preparation of conversion to kernfs, cgroup file handling is
updated so that it can be easily mapped to kernfs.  This patch renames
cgroup_pidlist_open_file to cgroup_open_file and updates it so that it
only contains a field to identify the specific file, ->cfe, and an
opaque ->priv pointer.  When cgroup is converted to kernfs, this will
be replaced by kernfs_open_file which contains about the same
information.

As whether the file is "cgroup.procs" or "tasks" should now be
determined from cgroup_open_file->cfe, the cftype->private for the two
files now carry the file type and cgroup_pidlist_start() reads the
type through cfe->type->private.  This makes the distinction between
cgroup_tasks_open() and cgroup_procs_open() unnecessary.
cgroup_pidlist_open() is now directly used as the open method.

This patch doesn't make any behavior changes.

v2: Refreshed on top of the updated "cgroup: introduce struct
    cgroup_pidlist_open_file".

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>

1 files changed, 30 insertions, 36 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index ce6db713bbd6..17272893d3b8 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3369,10 +3369,9 @@ struct cgroup_pidlist {
 };
 
 /* seq_file->private points to the following */
-struct cgroup_pidlist_open_file {
-        enum cgroup_filetype            type;
-        struct cgroup                   *cgrp;
-        struct cgroup_pidlist           *pidlist;
+struct cgroup_open_file {
+        struct cfent                    *cfe;
+        void                            *priv;
 };
 
 /*
@@ -3689,33 +3688,35 @@ static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
          * after a seek to the start). Use a binary-search to find the
          * next pid to display, if any
          */
-        struct cgroup_pidlist_open_file *of = s->private;
-        struct cgroup *cgrp = of->cgrp;
+        struct cgroup_open_file *of = s->private;
+        struct cgroup *cgrp = of->cfe->css->cgroup;
         struct cgroup_pidlist *l;
+        enum cgroup_filetype type = of->cfe->type->private;
         int index = 0, pid = *pos;
         int *iter, ret;
 
         mutex_lock(&cgrp->pidlist_mutex);
 
         /*
-         * !NULL @of->pidlist indicates that this isn't the first start()
+         * !NULL @of->priv indicates that this isn't the first start()
          * after open.  If the matching pidlist is around, we can use that.
-         * Look for it.  Note that @of->pidlist can't be used directly.  It
+         * Look for it.  Note that @of->priv can't be used directly.  It
          * could already have been destroyed.
          */
-        if (of->pidlist)
-                of->pidlist = cgroup_pidlist_find(cgrp, of->type);
+        if (of->priv)
+                of->priv = cgroup_pidlist_find(cgrp, type);
 
         /*
          * Either this is the first start() after open or the matching
          * pidlist has been destroyed inbetween.  Create a new one.
          */
-        if (!of->pidlist) {
-                ret = pidlist_array_load(of->cgrp, of->type, &of->pidlist);
+        if (!of->priv) {
+                ret = pidlist_array_load(cgrp, type,
+                                         (struct cgroup_pidlist **)&of->priv);
                 if (ret)
                         return ERR_PTR(ret);
         }
-        l = of->pidlist;
+        l = of->priv;
 
         if (pid) {
                 int end = l->length;
@@ -3742,19 +3743,19 @@ static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
 
 static void cgroup_pidlist_stop(struct seq_file *s, void *v)
 {
-        struct cgroup_pidlist_open_file *of = s->private;
+        struct cgroup_open_file *of = s->private;
+        struct cgroup_pidlist *l = of->priv;
 
-        if (of->pidlist)
-                mod_delayed_work(cgroup_pidlist_destroy_wq,
-                                 &of->pidlist->destroy_dwork,
+        if (l)
+                mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork,
                                  CGROUP_PIDLIST_DESTROY_DELAY);
-        mutex_unlock(&of->cgrp->pidlist_mutex);
+        mutex_unlock(&of->cfe->css->cgroup->pidlist_mutex);
 }
 
 static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
 {
-        struct cgroup_pidlist_open_file *of = s->private;
-        struct cgroup_pidlist *l = of->pidlist;
+        struct cgroup_open_file *of = s->private;
+        struct cgroup_pidlist *l = of->priv;
         pid_t *p = v;
         pid_t *end = l->list + l->length;
         /*
@@ -3765,7 +3766,7 @@ static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
         if (p >= end) {
                 return NULL;
         } else {
-                *pos = cgroup_pid_fry(of->cgrp, *p);
+                *pos = cgroup_pid_fry(of->cfe->css->cgroup, *p);
                 return p;
         }
 }
@@ -3799,10 +3800,10 @@ static const struct file_operations cgroup_pidlist_operations = {
  * in the cgroup.
  */
 /* helper function for the two below it */
-static int cgroup_pidlist_open(struct file *file, enum cgroup_filetype type)
+static int cgroup_pidlist_open(struct inode *unused, struct file *file)
 {
-        struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
-        struct cgroup_pidlist_open_file *of;
+        struct cfent *cfe = __d_cfe(file->f_dentry);
+        struct cgroup_open_file *of;
 
         /* configure file information */
         file->f_op = &cgroup_pidlist_operations;
@@ -3812,18 +3813,9 @@ static int cgroup_pidlist_open(struct file *file, enum cgroup_filetype type)
         if (!of)
                 return -ENOMEM;
 
-        of->type = type;
-        of->cgrp = cgrp;
+        of->cfe = cfe;
         return 0;
 }
-static int cgroup_tasks_open(struct inode *unused, struct file *file)
-{
-        return cgroup_pidlist_open(file, CGROUP_FILE_TASKS);
-}
-static int cgroup_procs_open(struct inode *unused, struct file *file)
-{
-        return cgroup_pidlist_open(file, CGROUP_FILE_PROCS);
-}
 
 static u64 cgroup_read_notify_on_release(struct cgroup_subsys_state *css,
                                          struct cftype *cft)
@@ -3878,7 +3870,8 @@ static int cgroup_clone_children_write(struct cgroup_subsys_state *css,
 static struct cftype cgroup_base_files[] = {
         {
                 .name = "cgroup.procs",
-                .open = cgroup_procs_open,
+                .open = cgroup_pidlist_open,
+                .private = CGROUP_FILE_PROCS,
                 .write_u64 = cgroup_procs_write,
                 .mode = S_IRUGO | S_IWUSR,
         },
@@ -3902,7 +3895,8 @@ static struct cftype cgroup_base_files[] = {
         {
                 .name = "tasks",
                 .flags = CFTYPE_INSANE,         /* use "procs" instead */
-                .open = cgroup_tasks_open,
+                .open = cgroup_pidlist_open,
+                .private = CGROUP_FILE_TASKS,
                 .write_u64 = cgroup_tasks_write,
                 .mode = S_IRUGO | S_IWUSR,
         },