[RFC][PATCH 2/7] CGroup API: Add cgroup map data type

[Paul Menage]

Adds a new type of supported control file representation, a map from
strings to u64 values.

Signed-off-by: Paul Menage <menage@xxxxxxxxxx>

---
 include/linux/cgroup.h |   19 +++++++++++++++
 kernel/cgroup.c        |   61 ++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 79 insertions(+), 1 deletion(-)

Index: cgroupmap-2.6.24-mm1/include/linux/cgroup.h
===================================================================
--- cgroupmap-2.6.24-mm1.orig/include/linux/cgroup.h
+++ cgroupmap-2.6.24-mm1/include/linux/cgroup.h
@@ -191,6 +191,17 @@ enum cgroup_file_type {
 	CGROUP_FILE_VOID,
 	CGROUP_FILE_U64,
 	CGROUP_FILE_STRING,
+	CGROUP_FILE_MAP,
+};
+
+/*
+ * 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;
 };
 
 #define MAX_CFTYPE_NAME 64
@@ -215,6 +226,14 @@ struct cftype {
 	 * single integer. Use it in place of read()
 	 */
 	u64 (*read_uint) (struct cgroup *cont, 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.
+	 */
+	int (*read_map) (struct cgroup *cont, struct cftype *cft,
+			 struct cgroup_map_cb *cb);
+
 	ssize_t (*write) (struct cgroup *cont, struct cftype *cft,
 			  struct file *file,
 			  const char __user *buf, size_t nbytes, loff_t *ppos);
Index: cgroupmap-2.6.24-mm1/kernel/cgroup.c
===================================================================
--- cgroupmap-2.6.24-mm1.orig/kernel/cgroup.c
+++ cgroupmap-2.6.24-mm1/kernel/cgroup.c
@@ -1488,6 +1488,46 @@ static ssize_t cgroup_file_read(struct f
 	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, 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,
+	};
+	if (cft->read_map) {
+		return cft->read_map(state->cgroup, cft, &cb);
+	} else {
+		BUG();
+	}
+}
+
+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;
+
 static int cgroup_file_open(struct inode *inode, struct file *file)
 {
 	int err;
@@ -1500,7 +1540,18 @@ static int cgroup_file_open(struct inode
 	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;
@@ -1539,6 +1590,12 @@ static struct file_operations cgroup_fil
 	.release = cgroup_file_release,
 };
 
+static struct file_operations cgroup_seqfile_operations = {
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = cgroup_seqfile_release,
+};
+
 static struct inode_operations cgroup_dir_inode_operations = {
 	.lookup = simple_lookup,
 	.mkdir = cgroup_mkdir,
@@ -2206,6 +2263,8 @@ static int cgroup_api_show(struct seq_fi
 	if (type == CGROUP_FILE_UNKNOWN) {
 		if (cft->read_uint)
 			type = CGROUP_FILE_U64;
+		else if (cft->read_map)
+			type = CGROUP_FILE_MAP;
 		else if (cft->read)
 			type = CGROUP_FILE_STRING;
 		else if (!cft->open)

--
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