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>

2 files changed, 15 insertions, 13 deletions

diff --git a/net/core/netprio_cgroup.c b/net/core/netprio_cgroup.c
index 3825f669147b..b990cefd906b 100644
--- a/net/core/netprio_cgroup.c
+++ b/net/core/netprio_cgroup.c
@@ -185,15 +185,15 @@ static int read_priomap(struct seq_file *sf, void *v)
         return 0;
 }
 
-static int write_priomap(struct cgroup_subsys_state *css, struct cftype *cft,
-                         char *buffer)
+static ssize_t write_priomap(struct kernfs_open_file *of,
+                             char *buf, size_t nbytes, loff_t off)
 {
         char devname[IFNAMSIZ + 1];
         struct net_device *dev;
         u32 prio;
         int ret;
 
-        if (sscanf(buffer, "%"__stringify(IFNAMSIZ)"s %u", devname, &prio) != 2)
+        if (sscanf(buf, "%"__stringify(IFNAMSIZ)"s %u", devname, &prio) != 2)
                 return -EINVAL;
 
         dev = dev_get_by_name(&init_net, devname);
@@ -202,11 +202,11 @@ static int write_priomap(struct cgroup_subsys_state *css, struct cftype *cft,
 
         rtnl_lock();
 
-        ret = netprio_set_prio(css, dev, prio);
+        ret = netprio_set_prio(of_css(of), dev, prio);
 
         rtnl_unlock();
         dev_put(dev);
-        return ret;
+        return ret ?: nbytes;
 }
 
 static int update_netprio(const void *v, struct file *file, unsigned n)
@@ -239,7 +239,7 @@ static struct cftype ss_files[] = {
         {
                 .name = "ifpriomap",
                 .seq_show = read_priomap,
-                .write_string = write_priomap,
+                .write = write_priomap,
         },
         { }     /* terminate */
 };
diff --git a/net/ipv4/tcp_memcontrol.c b/net/ipv4/tcp_memcontrol.c
index d4f015ad6c84..841fd3fa937a 100644
--- a/net/ipv4/tcp_memcontrol.c
+++ b/net/ipv4/tcp_memcontrol.c
@@ -102,17 +102,19 @@ static int tcp_update_limit(struct mem_cgroup *memcg, u64 val)
         return 0;
 }
 
-static int tcp_cgroup_write(struct cgroup_subsys_state *css, struct cftype *cft,
-                            char *buffer)
+static ssize_t tcp_cgroup_write(struct kernfs_open_file *of,
+                                char *buf, size_t nbytes, loff_t off)
 {
-        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
+        struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
         unsigned long long val;
         int ret = 0;
 
-        switch (cft->private) {
+        buf = strstrip(buf);
+
+        switch (of_cft(of)->private) {
         case RES_LIMIT:
                 /* see memcontrol.c */
-                ret = res_counter_memparse_write_strategy(buffer, &val);
+                ret = res_counter_memparse_write_strategy(buf, &val);
                 if (ret)
                         break;
                 ret = tcp_update_limit(memcg, val);
@@ -121,7 +123,7 @@ static int tcp_cgroup_write(struct cgroup_subsys_state *css, struct cftype *cft,
                 ret = -EINVAL;
                 break;
         }
-        return ret;
+        return ret ?: nbytes;
 }
 
 static u64 tcp_read_stat(struct mem_cgroup *memcg, int type, u64 default_val)
@@ -193,7 +195,7 @@ static int tcp_cgroup_reset(struct cgroup_subsys_state *css, unsigned int event)
 static struct cftype tcp_files[] = {
         {
                 .name = "kmem.tcp.limit_in_bytes",
-                .write_string = tcp_cgroup_write,
+                .write = tcp_cgroup_write,
                 .read_u64 = tcp_cgroup_read,
                 .private = RES_LIMIT,
         },