[PATCH] driver core: add a debugfs entry to show deferred devices

[javierm@redhat.com (Javier Martinez Canillas)]

For debugging purposes it may be useful to know what are the devices whose
probe function was deferred. Add a debugfs entry showing that information.

  $ cat /sys/kernel/debug/deferred_devices
  48070000.i2c:twl at 48:bci
  musb-hdrc.0.auto
  omapdrm.0

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>

---

Changes since RFC v1:
- Remove unneeded ret variable from deferred_devs_show()

Changes since RFC v2:
- Use DEFINE_SHOW_ATTRIBUTE() macro.
- Don't propagate debugfs_create_file() error.
- Remove IS_ENABLED(CONFIG_DEBUG_FS) guards.
- Drop RFC prefix.

 drivers/base/dd.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 1435d7281c6..8ec9e3cfbe4 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -16,6 +16,7 @@
  * Copyright (c) 2007-2009 Novell Inc.
  */
 
+#include <linux/debugfs.h>
 #include <linux/device.h>
 #include <linux/delay.h>
 #include <linux/dma-mapping.h>
@@ -224,6 +225,24 @@ void device_unblock_probing(void)
 	driver_deferred_probe_trigger();
 }
 
+/*
+ * deferred_devs_show() - Show the devices in the deferred probe pending list.
+ */
+static int deferred_devs_show(struct seq_file *s, void *data)
+{
+	struct device_private *curr;
+
+	mutex_lock(&deferred_probe_mutex);
+
+	list_for_each_entry(curr, &deferred_probe_pending_list, deferred_probe)
+		seq_printf(s, "%s\n", dev_name(curr->device));
+
+	mutex_unlock(&deferred_probe_mutex);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(deferred_devs);
+
 /**
  * deferred_probe_initcall() - Enable probing of deferred devices
  *
@@ -233,6 +252,9 @@ void device_unblock_probing(void)
  */
 static int deferred_probe_initcall(void)
 {
+	debugfs_create_file("deferred_devices", 0444, NULL, NULL,
+			    &deferred_devs_fops);
+
 	driver_deferred_probe_enable = true;
 	driver_deferred_probe_trigger();
 	/* Sort as many dependencies as possible before exiting initcalls */
-- 
2.17.1