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>

11 files changed, 124 insertions, 125 deletions

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 033745cd7fba..5e8fd1bace98 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -1346,10 +1346,10 @@ static int tg_print_conf_uint(struct seq_file *sf, void *v)
         return 0;
 }
 
-static int tg_set_conf(struct cgroup_subsys_state *css, struct cftype *cft,
-                       const char *buf, bool is_u64)
+static ssize_t tg_set_conf(struct kernfs_open_file *of,
+                           char *buf, size_t nbytes, loff_t off, bool is_u64)
 {
-        struct blkcg *blkcg = css_to_blkcg(css);
+        struct blkcg *blkcg = css_to_blkcg(of_css(of));
         struct blkg_conf_ctx ctx;
         struct throtl_grp *tg;
         struct throtl_service_queue *sq;
@@ -1368,9 +1368,9 @@ static int tg_set_conf(struct cgroup_subsys_state *css, struct cftype *cft,
                 ctx.v = -1;
 
         if (is_u64)
-                *(u64 *)((void *)tg + cft->private) = ctx.v;
+                *(u64 *)((void *)tg + of_cft(of)->private) = ctx.v;
         else
-                *(unsigned int *)((void *)tg + cft->private) = ctx.v;
+                *(unsigned int *)((void *)tg + of_cft(of)->private) = ctx.v;
 
         throtl_log(&tg->service_queue,
                    "limit change rbps=%llu wbps=%llu riops=%u wiops=%u",
@@ -1404,19 +1404,19 @@ static int tg_set_conf(struct cgroup_subsys_state *css, struct cftype *cft,
         }
 
         blkg_conf_finish(&ctx);
-        return 0;
+        return nbytes;
 }
 
-static int tg_set_conf_u64(struct cgroup_subsys_state *css, struct cftype *cft,
-                           char *buf)
+static ssize_t tg_set_conf_u64(struct kernfs_open_file *of,
+                               char *buf, size_t nbytes, loff_t off)
 {
-        return tg_set_conf(css, cft, buf, true);
+        return tg_set_conf(of, buf, nbytes, off, true);
 }
 
-static int tg_set_conf_uint(struct cgroup_subsys_state *css, struct cftype *cft,
-                            char *buf)
+static ssize_t tg_set_conf_uint(struct kernfs_open_file *of,
+                                char *buf, size_t nbytes, loff_t off)
 {
-        return tg_set_conf(css, cft, buf, false);
+        return tg_set_conf(of, buf, nbytes, off, false);
 }
 
 static struct cftype throtl_files[] = {
@@ -1424,25 +1424,25 @@ static struct cftype throtl_files[] = {
                 .name = "throttle.read_bps_device",
                 .private = offsetof(struct throtl_grp, bps[READ]),
                 .seq_show = tg_print_conf_u64,
-                .write_string = tg_set_conf_u64,
+                .write = tg_set_conf_u64,
         },
         {
                 .name = "throttle.write_bps_device",
                 .private = offsetof(struct throtl_grp, bps[WRITE]),
                 .seq_show = tg_print_conf_u64,
-                .write_string = tg_set_conf_u64,
+                .write = tg_set_conf_u64,
         },
         {
                 .name = "throttle.read_iops_device",
                 .private = offsetof(struct throtl_grp, iops[READ]),
                 .seq_show = tg_print_conf_uint,
-                .write_string = tg_set_conf_uint,
+                .write = tg_set_conf_uint,
         },
         {
                 .name = "throttle.write_iops_device",
                 .private = offsetof(struct throtl_grp, iops[WRITE]),
                 .seq_show = tg_print_conf_uint,
-                .write_string = tg_set_conf_uint,
+                .write = tg_set_conf_uint,
         },
         {
                 .name = "throttle.io_service_bytes",
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index e0985f1955e7..a73020b8c9af 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1670,11 +1670,11 @@ static int cfq_print_leaf_weight(struct seq_file *sf, void *v)
         return 0;
 }
 
-static int __cfqg_set_weight_device(struct cgroup_subsys_state *css,
-                                    struct cftype *cft, const char *buf,
-                                    bool is_leaf_weight)
+static ssize_t __cfqg_set_weight_device(struct kernfs_open_file *of,
+                                        char *buf, size_t nbytes, loff_t off,
+                                        bool is_leaf_weight)
 {
-        struct blkcg *blkcg = css_to_blkcg(css);
+        struct blkcg *blkcg = css_to_blkcg(of_css(of));
         struct blkg_conf_ctx ctx;
         struct cfq_group *cfqg;
         int ret;
@@ -1697,19 +1697,19 @@ static int __cfqg_set_weight_device(struct cgroup_subsys_state *css,
         }
 
         blkg_conf_finish(&ctx);
-        return ret;
+        return ret ?: nbytes;
 }
 
-static int cfqg_set_weight_device(struct cgroup_subsys_state *css,
-                                  struct cftype *cft, char *buf)
+static ssize_t cfqg_set_weight_device(struct kernfs_open_file *of,
+                                      char *buf, size_t nbytes, loff_t off)
 {
-        return __cfqg_set_weight_device(css, cft, buf, false);
+        return __cfqg_set_weight_device(of, buf, nbytes, off, false);
 }
 
-static int cfqg_set_leaf_weight_device(struct cgroup_subsys_state *css,
-                                       struct cftype *cft, char *buf)
+static ssize_t cfqg_set_leaf_weight_device(struct kernfs_open_file *of,
+                                           char *buf, size_t nbytes, loff_t off)
 {
-        return __cfqg_set_weight_device(css, cft, buf, true);
+        return __cfqg_set_weight_device(of, buf, nbytes, off, true);
 }
 
 static int __cfq_set_weight(struct cgroup_subsys_state *css, struct cftype *cft,
@@ -1837,7 +1837,7 @@ static struct cftype cfq_blkcg_files[] = {
                 .name = "weight_device",
                 .flags = CFTYPE_ONLY_ON_ROOT,
                 .seq_show = cfqg_print_leaf_weight_device,
-                .write_string = cfqg_set_leaf_weight_device,
+                .write = cfqg_set_leaf_weight_device,
         },
         {
                 .name = "weight",
@@ -1851,7 +1851,7 @@ static struct cftype cfq_blkcg_files[] = {
                 .name = "weight_device",
                 .flags = CFTYPE_NOT_ON_ROOT,
                 .seq_show = cfqg_print_weight_device,
-                .write_string = cfqg_set_weight_device,
+                .write = cfqg_set_weight_device,
         },
         {
                 .name = "weight",
@@ -1863,7 +1863,7 @@ static struct cftype cfq_blkcg_files[] = {
         {
                 .name = "leaf_weight_device",
                 .seq_show = cfqg_print_leaf_weight_device,
-                .write_string = cfqg_set_leaf_weight_device,
+                .write = cfqg_set_leaf_weight_device,
         },
         {
                 .name = "leaf_weight",
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index c5a170ca4a48..aecdc84fe128 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -453,8 +453,7 @@ struct cftype {
 
         /*
          * The maximum length of string, excluding trailing nul, that can
-         * be passed to write_string.  If < PAGE_SIZE-1, PAGE_SIZE-1 is
-         * assumed.
+         * be passed to write.  If < PAGE_SIZE-1, PAGE_SIZE-1 is assumed.
          */
         size_t max_write_len;
 
@@ -501,13 +500,6 @@ struct cftype {
                          s64 val);
 
         /*
-         * write_string() is passed a nul-terminated kernelspace
-         * buffer of maximum length determined by max_write_len.
-         * Returns 0 or -ve error code.
-         */
-        int (*write_string)(struct cgroup_subsys_state *css, struct cftype *cft,
-                            char *buffer);
-        /*
          * trigger() callback can be used to get some kick from the
          * userspace, when the actual string written is not important
          * at all. The private field can be used to determine the
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 */
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 0398f7e9ac81..6b4e60e33a9a 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -73,10 +73,6 @@ bool cgroup_freezing(struct task_struct *task)
         return ret;
 }
 
-/*
- * cgroups_write_string() limits the size of freezer state strings to
- * CGROUP_LOCAL_BUFFER_SIZE
- */
 static const char *freezer_state_strs(unsigned int state)
 {
         if (state & CGROUP_FROZEN)
@@ -423,20 +419,22 @@ static void freezer_change_state(struct freezer *freezer, bool freeze)
         mutex_unlock(&freezer_mutex);
 }
 
-static int freezer_write(struct cgroup_subsys_state *css, struct cftype *cft,
-                         char *buffer)
+static ssize_t freezer_write(struct kernfs_open_file *of,
+                             char *buf, size_t nbytes, loff_t off)
 {
         bool freeze;
 
-        if (strcmp(buffer, freezer_state_strs(0)) == 0)
+        buf = strstrip(buf);
+
+        if (strcmp(buf, freezer_state_strs(0)) == 0)
                 freeze = false;
-        else if (strcmp(buffer, freezer_state_strs(CGROUP_FROZEN)) == 0)
+        else if (strcmp(buf, freezer_state_strs(CGROUP_FROZEN)) == 0)
                 freeze = true;
         else
                 return -EINVAL;
 
-        freezer_change_state(css_freezer(css), freeze);
-        return 0;
+        freezer_change_state(css_freezer(of_css(of)), freeze);
+        return nbytes;
 }
 
 static u64 freezer_self_freezing_read(struct cgroup_subsys_state *css,
@@ -460,7 +458,7 @@ static struct cftype files[] = {
                 .name = "state",
                 .flags = CFTYPE_NOT_ON_ROOT,
                 .seq_show = freezer_read,
-                .write_string = freezer_write,
+                .write = freezer_write,
         },
         {
                 .name = "self_freezing",
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 37ca0a5c226d..2f4b08b8db24 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1603,13 +1603,15 @@ out_unlock:
 /*
  * Common handling for a write to a "cpus" or "mems" file.
  */
-static int cpuset_write_resmask(struct cgroup_subsys_state *css,
-                                struct cftype *cft, char *buf)
+static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
+                                    char *buf, size_t nbytes, loff_t off)
 {
-        struct cpuset *cs = css_cs(css);
+        struct cpuset *cs = css_cs(of_css(of));
         struct cpuset *trialcs;
         int retval = -ENODEV;
 
+        buf = strstrip(buf);
+
         /*
          * CPU or memory hotunplug may leave @cs w/o any execution
          * resources, in which case the hotplug code asynchronously updates
@@ -1633,7 +1635,7 @@ static int cpuset_write_resmask(struct cgroup_subsys_state *css,
                 goto out_unlock;
         }
 
-        switch (cft->private) {
+        switch (of_cft(of)->private) {
         case FILE_CPULIST:
                 retval = update_cpumask(cs, trialcs, buf);
                 break;
@@ -1648,7 +1650,7 @@ static int cpuset_write_resmask(struct cgroup_subsys_state *css,
         free_trial_cpuset(trialcs);
 out_unlock:
         mutex_unlock(&cpuset_mutex);
-        return retval;
+        return retval ?: nbytes;
 }
 
 /*
@@ -1750,7 +1752,7 @@ static struct cftype files[] = {
         {
                 .name = "cpus",
                 .seq_show = cpuset_common_seq_show,
-                .write_string = cpuset_write_resmask,
+                .write = cpuset_write_resmask,
                 .max_write_len = (100U + 6 * NR_CPUS),
                 .private = FILE_CPULIST,
         },
@@ -1758,7 +1760,7 @@ static struct cftype files[] = {
         {
                 .name = "mems",
                 .seq_show = cpuset_common_seq_show,
-                .write_string = cpuset_write_resmask,
+                .write = cpuset_write_resmask,
                 .max_write_len = (100U + 6 * MAX_NUMNODES),
                 .private = FILE_MEMLIST,
         },
diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index 372f1adca491..191de26b0148 100644
--- a/mm/hugetlb_cgroup.c
+++ b/mm/hugetlb_cgroup.c
@@ -253,15 +253,16 @@ static u64 hugetlb_cgroup_read_u64(struct cgroup_subsys_state *css,
         return res_counter_read_u64(&h_cg->hugepage[idx], name);
 }
 
-static int hugetlb_cgroup_write(struct cgroup_subsys_state *css,
-                                struct cftype *cft, char *buffer)
+static ssize_t hugetlb_cgroup_write(struct kernfs_open_file *of,
+                                    char *buf, size_t nbytes, loff_t off)
 {
         int idx, name, ret;
         unsigned long long val;
-        struct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_css(css);
+        struct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_css(of_css(of));
 
-        idx = MEMFILE_IDX(cft->private);
-        name = MEMFILE_ATTR(cft->private);
+        buf = strstrip(buf);
+        idx = MEMFILE_IDX(of_cft(of)->private);
+        name = MEMFILE_ATTR(of_cft(of)->private);
 
         switch (name) {
         case RES_LIMIT:
@@ -271,7 +272,7 @@ static int hugetlb_cgroup_write(struct cgroup_subsys_state *css,
                         break;
                 }
                 /* This function does all necessary parse...reuse it */
-                ret = res_counter_memparse_write_strategy(buffer, &val);
+                ret = res_counter_memparse_write_strategy(buf, &val);
                 if (ret)
                         break;
                 ret = res_counter_set_limit(&h_cg->hugepage[idx], val);
@@ -280,7 +281,7 @@ static int hugetlb_cgroup_write(struct cgroup_subsys_state *css,
                 ret = -EINVAL;
                 break;
         }
-        return ret;
+        return ret ?: nbytes;
 }
 
 static int hugetlb_cgroup_reset(struct cgroup_subsys_state *css,
@@ -331,7 +332,7 @@ static void __init __hugetlb_cgroup_file_init(int idx)
         snprintf(cft->name, MAX_CFTYPE_NAME, "%s.limit_in_bytes", buf);
         cft->private = MEMFILE_PRIVATE(idx, RES_LIMIT);
         cft->read_u64 = hugetlb_cgroup_read_u64;
-        cft->write_string = hugetlb_cgroup_write;
+        cft->write = hugetlb_cgroup_write;
 
         /* Add the usage file */
         cft = &h->cgroup_files[1];
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 5cf3246314a2..7098a43f7447 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5143,17 +5143,18 @@ static int memcg_update_kmem_limit(struct mem_cgroup *memcg,
  * The user of this function is...
  * RES_LIMIT.
  */
-static int mem_cgroup_write(struct cgroup_subsys_state *css, struct cftype *cft,
-                            char *buffer)
+static ssize_t mem_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));
         enum res_type type;
         int name;
         unsigned long long val;
         int ret;
 
-        type = MEMFILE_TYPE(cft->private);
-        name = MEMFILE_ATTR(cft->private);
+        buf = strstrip(buf);
+        type = MEMFILE_TYPE(of_cft(of)->private);
+        name = MEMFILE_ATTR(of_cft(of)->private);
 
         switch (name) {
         case RES_LIMIT:
@@ -5162,7 +5163,7 @@ static int mem_cgroup_write(struct cgroup_subsys_state *css, struct cftype *cft,
                         break;
                 }
                 /* This function does all necessary parse...reuse it */
-                ret = res_counter_memparse_write_strategy(buffer, &val);
+                ret = res_counter_memparse_write_strategy(buf, &val);
                 if (ret)
                         break;
                 if (type == _MEM)
@@ -5175,7 +5176,7 @@ static int mem_cgroup_write(struct cgroup_subsys_state *css, struct cftype *cft,
                         return -EINVAL;
                 break;
         case RES_SOFT_LIMIT:
-                ret = res_counter_memparse_write_strategy(buffer, &val);
+                ret = res_counter_memparse_write_strategy(buf, &val);
                 if (ret)
                         break;
                 /*
@@ -5192,7 +5193,7 @@ static int mem_cgroup_write(struct cgroup_subsys_state *css, struct cftype *cft,
                 ret = -EINVAL; /* should be BUG() ? */
                 break;
         }
-        return ret;
+        return ret ?: nbytes;
 }
 
 static void memcg_get_hierarchical_limit(struct mem_cgroup *memcg,
@@ -5964,9 +5965,10 @@ static void memcg_event_ptable_queue_proc(struct file *file,
  * Input must be in format '<event_fd> <control_fd> <args>'.
  * Interpretation of args is defined by control file implementation.
  */
-static int memcg_write_event_control(struct cgroup_subsys_state *css,
-                                     struct cftype *cft, char *buffer)
+static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
+                                         char *buf, size_t nbytes, loff_t off)
 {
+        struct cgroup_subsys_state *css = of_css(of);
         struct mem_cgroup *memcg = mem_cgroup_from_css(css);
         struct mem_cgroup_event *event;
         struct cgroup_subsys_state *cfile_css;
@@ -5977,15 +5979,17 @@ static int memcg_write_event_control(struct cgroup_subsys_state *css,
         char *endp;
         int ret;
 
-        efd = simple_strtoul(buffer, &endp, 10);
+        buf = strstrip(buf);
+
+        efd = simple_strtoul(buf, &endp, 10);
         if (*endp != ' ')
                 return -EINVAL;
-        buffer = endp + 1;
+        buf = endp + 1;
 
-        cfd = simple_strtoul(buffer, &endp, 10);
+        cfd = simple_strtoul(buf, &endp, 10);
         if ((*endp != ' ') && (*endp != '\0'))
                 return -EINVAL;
-        buffer = endp + 1;
+        buf = endp + 1;
 
         event = kzalloc(sizeof(*event), GFP_KERNEL);
         if (!event)
@@ -6063,7 +6067,7 @@ static int memcg_write_event_control(struct cgroup_subsys_state *css,
                 goto out_put_cfile;
         }
 
-        ret = event->register_event(memcg, event->eventfd, buffer);
+        ret = event->register_event(memcg, event->eventfd, buf);
         if (ret)
                 goto out_put_css;
 
@@ -6076,7 +6080,7 @@ static int memcg_write_event_control(struct cgroup_subsys_state *css,
         fdput(cfile);
         fdput(efile);
 
-        return 0;
+        return nbytes;
 
 out_put_css:
         css_put(css);
@@ -6107,13 +6111,13 @@ static struct cftype mem_cgroup_files[] = {
         {
                 .name = "limit_in_bytes",
                 .private = MEMFILE_PRIVATE(_MEM, RES_LIMIT),
-                .write_string = mem_cgroup_write,
+                .write = mem_cgroup_write,
                 .read_u64 = mem_cgroup_read_u64,
         },
         {
                 .name = "soft_limit_in_bytes",
                 .private = MEMFILE_PRIVATE(_MEM, RES_SOFT_LIMIT),
-                .write_string = mem_cgroup_write,
+                .write = mem_cgroup_write,
                 .read_u64 = mem_cgroup_read_u64,
         },
         {
@@ -6138,7 +6142,7 @@ static struct cftype mem_cgroup_files[] = {
         },
         {
                 .name = "cgroup.event_control",         /* XXX: for compat */
-                .write_string = memcg_write_event_control,
+                .write = memcg_write_event_control,
                 .flags = CFTYPE_NO_PREFIX,
                 .mode = S_IWUGO,
         },
@@ -6171,7 +6175,7 @@ static struct cftype mem_cgroup_files[] = {
         {
                 .name = "kmem.limit_in_bytes",
                 .private = MEMFILE_PRIVATE(_KMEM, RES_LIMIT),
-                .write_string = mem_cgroup_write,
+                .write = mem_cgroup_write,
                 .read_u64 = mem_cgroup_read_u64,
         },
         {
@@ -6217,7 +6221,7 @@ static struct cftype memsw_cgroup_files[] = {
         {
                 .name = "memsw.limit_in_bytes",
                 .private = MEMFILE_PRIVATE(_MEMSWAP, RES_LIMIT),
-                .write_string = mem_cgroup_write,
+                .write = mem_cgroup_write,
                 .read_u64 = mem_cgroup_read_u64,
         },
         {
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,
         },
diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 9134dbf70d3e..7dbac4061b1c 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -767,27 +767,27 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
         return rc;
 }
 
-static int devcgroup_access_write(struct cgroup_subsys_state *css,
-                                  struct cftype *cft, char *buffer)
+static ssize_t devcgroup_access_write(struct kernfs_open_file *of,
+                                      char *buf, size_t nbytes, loff_t off)
 {
         int retval;
 
         mutex_lock(&devcgroup_mutex);
-        retval = devcgroup_update_access(css_to_devcgroup(css),
-                                         cft->private, buffer);
+        retval = devcgroup_update_access(css_to_devcgroup(of_css(of)),
+                                         of_cft(of)->private, strstrip(buf));
         mutex_unlock(&devcgroup_mutex);
-        return retval;
+        return retval ?: nbytes;
 }
 
 static struct cftype dev_cgroup_files[] = {
         {
                 .name = "allow",
-                .write_string  = devcgroup_access_write,
+                .write = devcgroup_access_write,
                 .private = DEVCG_ALLOW,
         },
         {
                 .name = "deny",
-                .write_string = devcgroup_access_write,
+                .write = devcgroup_access_write,
                 .private = DEVCG_DENY,
         },
         {