cgroup: replace cftype->write_string() with cftype->write()

Convert all cftype->write_string() users to the new cftype->write()
which maps directly to kernfs write operation and has full access to
kernfs and cgroup contexts.  The conversions are mostly mechanical.

* @css and @cft are accessed using of_css() and of_cft() accessors
  respectively instead of being specified as arguments.

* Should return @nbytes on success instead of 0.

* @buf is not trimmed automatically.  Trim if necessary.  Note that
  blkcg and netprio don't need this as the parsers already handle
  whitespaces.

cftype->write_string() has no user left after the conversions and
removed.

While at it, remove unnecessary local variable @p in
cgroup_subtree_control_write() and stale comment about
CGROUP_LOCAL_BUFFER_SIZE in cgroup_freezer.c.

This patch doesn't introduce any visible behavior changes.

v2: netprio was missing from conversion.  Converted.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Aristeu Rozanski <arozansk@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Neil Horman <nhorman@tuxdriver.com>
Cc: "David S. Miller" <davem@davemloft.net>

1 files changed, 19 insertions, 19 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index a16f91d12f4e..2a88ce7b24b6 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1035,7 +1035,7 @@ static umode_t cgroup_file_mode(const struct cftype *cft)
                 mode |= S_IRUGO;
 
         if (cft->write_u64 || cft->write_s64 || cft->write ||
-            cft->write_string || cft->trigger)
+            cft->trigger)
                 mode |= S_IWUSR;
 
         return mode;
@@ -2352,20 +2352,21 @@ static int cgroup_procs_write(struct cgroup_subsys_state *css,
         return attach_task_by_pid(css->cgroup, tgid, true);
 }
 
-static int cgroup_release_agent_write(struct cgroup_subsys_state *css,
-                                      struct cftype *cft, char *buffer)
+static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of,
+                                          char *buf, size_t nbytes, loff_t off)
 {
-        struct cgroup_root *root = css->cgroup->root;
+        struct cgroup *cgrp = of_css(of)->cgroup;
+        struct cgroup_root *root = cgrp->root;
 
         BUILD_BUG_ON(sizeof(root->release_agent_path) < PATH_MAX);
-        if (!cgroup_lock_live_group(css->cgroup))
+        if (!cgroup_lock_live_group(cgrp))
                 return -ENODEV;
         spin_lock(&release_agent_path_lock);
-        strlcpy(root->release_agent_path, buffer,
+        strlcpy(root->release_agent_path, strstrip(buf),
                 sizeof(root->release_agent_path));
         spin_unlock(&release_agent_path_lock);
         mutex_unlock(&cgroup_mutex);
-        return 0;
+        return nbytes;
 }
 
 static int cgroup_release_agent_show(struct seq_file *seq, void *v)
@@ -2530,21 +2531,22 @@ out_finish:
 }
 
 /* change the enabled child controllers for a cgroup in the default hierarchy */
-static int cgroup_subtree_control_write(struct cgroup_subsys_state *dummy_css,
-                                        struct cftype *cft, char *buffer)
+static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
+                                            char *buf, size_t nbytes,
+                                            loff_t off)
 {
         unsigned int enable = 0, disable = 0;
-        struct cgroup *cgrp = dummy_css->cgroup, *child;
+        struct cgroup *cgrp = of_css(of)->cgroup, *child;
         struct cgroup_subsys *ss;
-        char *tok, *p;
+        char *tok;
         int ssid, ret;
 
         /*
          * Parse input - space separated list of subsystem names prefixed
          * with either + or -.
          */
-        p = buffer;
-        while ((tok = strsep(&p, " "))) {
+        buf = strstrip(buf);
+        while ((tok = strsep(&buf, " "))) {
                 if (tok[0] == '\0')
                         continue;
                 for_each_subsys(ss, ssid) {
@@ -2692,7 +2694,7 @@ out_unlock_tree:
 out_unbreak:
         kernfs_unbreak_active_protection(cgrp->control_kn);
         cgroup_put(cgrp);
-        return ret;
+        return ret ?: nbytes;
 
 err_undo_css:
         cgrp->child_subsys_mask &= ~enable;
@@ -2738,9 +2740,7 @@ static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
         css = cgroup_css(cgrp, cft->ss);
         rcu_read_unlock();
 
-        if (cft->write_string) {
-                ret = cft->write_string(css, cft, strstrip(buf));
-        } else if (cft->write_u64) {
+        if (cft->write_u64) {
                 unsigned long long v;
                 ret = kstrtoull(buf, 0, &v);
                 if (!ret)
@@ -3984,7 +3984,7 @@ static struct cftype cgroup_base_files[] = {
                 .name = "cgroup.subtree_control",
                 .flags = CFTYPE_ONLY_ON_DFL,
                 .seq_show = cgroup_subtree_control_show,
-                .write_string = cgroup_subtree_control_write,
+                .write = cgroup_subtree_control_write,
         },
         {
                 .name = "cgroup.populated",
@@ -4018,7 +4018,7 @@ static struct cftype cgroup_base_files[] = {
                 .name = "release_agent",
                 .flags = CFTYPE_INSANE | CFTYPE_ONLY_ON_ROOT,
                 .seq_show = cgroup_release_agent_show,
-                .write_string = cgroup_release_agent_write,
+                .write = cgroup_release_agent_write,
                 .max_write_len = PATH_MAX - 1,
         },
         { }     /* terminate */