cgroup: implement cftype->write()

During the recent conversion to kernfs, cftype's seq_file operations
are updated so that they are directly mapped to kernfs operations and
thus can fully access the associated kernfs and cgroup contexts;
however, write path hasn't seen similar updates and none of the
existing write operations has access to, for example, the associated
kernfs_open_file.

Let's introduce a new operation cftype->write() which maps directly to
the kernfs write operation and has access to all the arguments and
contexts.  This will replace ->write_string() and ->trigger() and ease
manipulation of kernfs active protection from cgroup file operations.

Two accessors - of_cft() and of_css() - are introduced to enable
accessing the associated cgroup context from cftype->write() which
only takes kernfs_open_file for the context information.  The
accessors for seq_file operations - seq_cft() and seq_css() - are
rewritten to wrap the of_ accessors.

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

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index c5f3684ef557201cb242eeea44406ad45827650c..c5a170ca4a48cd82bcb3a1a2439ffef4503e5d85 100644 (file)
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -515,6 +515,15 @@ struct cftype {
         */
        int (*trigger)(struct cgroup_subsys_state *css, unsigned int event);
 
+       /*
+        * write() is the generic write callback which maps directly to
+        * kernfs write operation and overrides all other operations.
+        * Maximum write size is determined by ->max_write_len.  Use
+        * of_css/cft() to access the associated css and cft.
+        */
+       ssize_t (*write)(struct kernfs_open_file *of,
+                        char *buf, size_t nbytes, loff_t off);
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
        struct lock_class_key   lockdep_key;
 #endif
@@ -552,14 +561,24 @@ static inline ino_t cgroup_ino(struct cgroup *cgrp)
                return 0;
 }
 
-static inline struct cftype *seq_cft(struct seq_file *seq)
+/* cft/css accessors for cftype->write() operation */
+static inline struct cftype *of_cft(struct kernfs_open_file *of)
 {
-       struct kernfs_open_file *of = seq->private;
-
        return of->kn->priv;
 }
 
-struct cgroup_subsys_state *seq_css(struct seq_file *seq);
+struct cgroup_subsys_state *of_css(struct kernfs_open_file *of);
+
+/* cft/css accessors for cftype->seq_*() operations */
+static inline struct cftype *seq_cft(struct seq_file *seq)
+{
+       return of_cft(seq->private);
+}
+
+static inline struct cgroup_subsys_state *seq_css(struct seq_file *seq)
+{
+       return of_css(seq->private);
+}
 
 /*
  * Name / path handling functions.  All are thin wrappers around the kernfs

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 671d8a6dae37e011ea812ee6a6304c1bd633161e..a16f91d12f4e0cd2b04f107eea729ec3fc17491d 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -283,11 +283,10 @@ static inline bool cgroup_is_dead(const struct cgroup *cgrp)
        return test_bit(CGRP_DEAD, &cgrp->flags);
 }
 
-struct cgroup_subsys_state *seq_css(struct seq_file *seq)
+struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)
 {
-       struct kernfs_open_file *of = seq->private;
        struct cgroup *cgrp = of->kn->parent->priv;
-       struct cftype *cft = seq_cft(seq);
+       struct cftype *cft = of_cft(of);
 
        /*
         * This is open and unprotected implementation of cgroup_css().
@@ -302,7 +301,7 @@ struct cgroup_subsys_state *seq_css(struct seq_file *seq)
        else
                return &cgrp->dummy_css;
 }
-EXPORT_SYMBOL_GPL(seq_css);
+EXPORT_SYMBOL_GPL(of_css);
 
 /**
  * cgroup_is_descendant - test ancestry
@@ -1035,8 +1034,8 @@ static umode_t cgroup_file_mode(const struct cftype *cft)
        if (cft->read_u64 || cft->read_s64 || cft->seq_show)
                mode |= S_IRUGO;
 
-       if (cft->write_u64 || cft->write_s64 || cft->write_string ||
-           cft->trigger)
+       if (cft->write_u64 || cft->write_s64 || cft->write ||
+           cft->write_string || cft->trigger)
                mode |= S_IWUSR;
 
        return mode;
@@ -2726,6 +2725,9 @@ static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
        struct cgroup_subsys_state *css;
        int ret;
 
+       if (cft->write)
+               return cft->write(of, buf, nbytes, off);
+
        /*
         * kernfs guarantees that a file isn't deleted with operations in
         * flight, which means that the matching css is and stays alive and