2 files changed, 71 insertions, 1 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 058371c5d360..0a3ab670dd2f 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -166,6 +166,16 @@ struct css_set {
 
 };
 
+/*
+ * cgroup_map_cb is an abstract callback API for reporting map-valued
+ * control files
+ */
+
+struct cgroup_map_cb {
+        int (*fill)(struct cgroup_map_cb *cb, const char *key, u64 value);
+        void *state;
+};
+
 /* struct cftype:
  *
  * The files in the cgroup filesystem mostly have a very simple read/write
@@ -194,6 +204,15 @@ struct cftype {
          * single integer. Use it in place of read()
          */
         u64 (*read_u64) (struct cgroup *cgrp, struct cftype *cft);
+        /*
+         * read_map() is used for defining a map of key/value
+         * pairs. It should call cb->fill(cb, key, value) for each
+         * entry. The key/value pairs (and their ordering) should not
+         * change between reboots.
+         */
+        int (*read_map) (struct cgroup *cont, struct cftype *cft,
+                         struct cgroup_map_cb *cb);
+
         ssize_t (*write) (struct cgroup *cgrp, struct cftype *cft,
                           struct file *file,
                           const char __user *buf, size_t nbytes, loff_t *ppos);
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 57afdde871ac..693bcc03188b 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1492,6 +1492,46 @@ static ssize_t cgroup_file_read(struct file *file, char __user *buf,
         return -EINVAL;
 }
 
+/*
+ * seqfile ops/methods for returning structured data. Currently just
+ * supports string->u64 maps, but can be extended in future.
+ */
+
+struct cgroup_seqfile_state {
+        struct cftype *cft;
+        struct cgroup *cgroup;
+};
+
+static int cgroup_map_add(struct cgroup_map_cb *cb, const char *key, u64 value)
+{
+        struct seq_file *sf = cb->state;
+        return seq_printf(sf, "%s %llu\n", key, (unsigned long long)value);
+}
+
+static int cgroup_seqfile_show(struct seq_file *m, void *arg)
+{
+        struct cgroup_seqfile_state *state = m->private;
+        struct cftype *cft = state->cft;
+        struct cgroup_map_cb cb = {
+                .fill = cgroup_map_add,
+                .state = m,
+        };
+        return cft->read_map(state->cgroup, cft, &cb);
+}
+
+int cgroup_seqfile_release(struct inode *inode, struct file *file)
+{
+        struct seq_file *seq = file->private_data;
+        kfree(seq->private);
+        return single_release(inode, file);
+}
+
+static struct file_operations cgroup_seqfile_operations = {
+        .read = seq_read,
+        .llseek = seq_lseek,
+        .release = cgroup_seqfile_release,
+};
+
 static int cgroup_file_open(struct inode *inode, struct file *file)
 {
         int err;
@@ -1504,7 +1544,18 @@ static int cgroup_file_open(struct inode *inode, struct file *file)
         cft = __d_cft(file->f_dentry);
         if (!cft)
                 return -ENODEV;
-        if (cft->open)
+        if (cft->read_map) {
+                struct cgroup_seqfile_state *state =
+                        kzalloc(sizeof(*state), GFP_USER);
+                if (!state)
+                        return -ENOMEM;
+                state->cft = cft;
+                state->cgroup = __d_cgrp(file->f_dentry->d_parent);
+                file->f_op = &cgroup_seqfile_operations;
+                err = single_open(file, cgroup_seqfile_show, state);
+                if (err < 0)
+                        kfree(state);
+        } else if (cft->open)
                 err = cft->open(inode, file);
         else
                 err = 0;