[PATCH v5] component: add debugfs support

[Maciej Purski]

Currently there is no information in any vfs about which devices
a master component consists of, what makes debugging hard if
one of the component devices fails to register.

Add 'device_component' directory to debugfs. Create a new file for each
component master, when it has been added. Remove it on a master
deletion. Show a list of devices required by the given master and their
status (registered or not). This provides an easy way to check, which
device has failed to register if the given master device is not
available in the system.

Signed-off-by: Maciej Purski <m.purski@xxxxxxxxxxx>
---
Changes in v5:
- remove inline of no-op functions

Changes in v4:
- fix and expand commit message
- inline n-op functions

Changes in v3:
- get rid of useless check
- change directory name to "device_component"

Changes in v2:
- use seq_printf() instead of seq_puts() when printing headers
- move whole debugfs code to the file beginning in order to avoid
  forward declarations or using multiple ifdefs
---
 drivers/base/component.c | 78 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 78 insertions(+)

diff --git a/drivers/base/component.c b/drivers/base/component.c
index 89b032f..114a602 100644
--- a/drivers/base/component.c
+++ b/drivers/base/component.c
@@ -17,6 +17,7 @@
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/slab.h>
+#include <linux/debugfs.h>
 
 struct component;
 
@@ -41,6 +42,7 @@ struct master {
 	const struct component_master_ops *ops;
 	struct device *dev;
 	struct component_match *match;
+	struct dentry *dentry;
 };
 
 struct component {
@@ -56,6 +58,80 @@ static DEFINE_MUTEX(component_mutex);
 static LIST_HEAD(component_list);
 static LIST_HEAD(masters);
 
+#ifdef CONFIG_DEBUG_FS
+
+static struct dentry *component_debugfs_dir;
+
+static int component_devices_show(struct seq_file *s, void *data)
+{
+	struct master *m = s->private;
+	struct component_match *match = m->match;
+	size_t i;
+
+	mutex_lock(&component_mutex);
+	seq_printf(s, "%-40s %20s\n", "master name", "status");
+	seq_puts(s, "-------------------------------------------------------------\n");
+	seq_printf(s, "%-40s %20s\n\n",
+		   dev_name(m->dev), m->bound ? "bound" : "not bound");
+
+	seq_printf(s, "%-40s %20s\n", "device name", "status");
+	seq_puts(s, "-------------------------------------------------------------\n");
+	for (i = 0; i < match->num; i++) {
+		struct device *d = (struct device *)match->compare[i].data;
+
+		seq_printf(s, "%-40s %20s\n", dev_name(d),
+			   match->compare[i].component ?
+			   "registered" : "not registered");
+	}
+	mutex_unlock(&component_mutex);
+
+	return 0;
+}
+
+static int component_devices_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, component_devices_show, inode->i_private);
+}
+
+static const struct file_operations component_devices_fops = {
+	.open = component_devices_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = single_release,
+};
+
+static int __init component_debug_init(void)
+{
+	component_debugfs_dir = debugfs_create_dir("device_component", NULL);
+
+	return 0;
+}
+
+core_initcall(component_debug_init);
+
+static void component_master_debugfs_add(struct master *m)
+{
+	m->dentry = debugfs_create_file(dev_name(m->dev), 0444,
+					component_debugfs_dir,
+					m, &component_devices_fops);
+}
+
+static void component_master_debugfs_del(struct master *m)
+{
+	debugfs_remove(m->dentry);
+	m->dentry = NULL;
+}
+
+#else
+
+static void component_master_debugfs_add(struct master *m)
+{ }
+
+static void component_master_debugfs_del(struct master *m)
+{ }
+
+#endif
+
 static struct master *__master_find(struct device *dev,
 	const struct component_master_ops *ops)
 {
@@ -290,6 +366,7 @@ static void free_master(struct master *master)
 	struct component_match *match = master->match;
 	int i;
 
+	component_master_debugfs_del(master);
 	list_del(&master->node);
 
 	if (match) {
@@ -323,6 +400,7 @@ int component_master_add_with_match(struct device *dev,
 	master->ops = ops;
 	master->match = match;
 
+	component_master_debugfs_add(master);
 	/* Add to the list of available masters. */
 	mutex_lock(&component_mutex);
 	list_add(&master->node, &masters);
-- 
2.7.4