[PATCH v2] USB: gadget: Add ID numbers to configfs-gadget driver names

[Chanh Nguyen <chanh@xxxxxxxxxxxxxxxxxxxxxx>]

It is unable to use configfs to attach more than one gadget. When
attaching the second gadget, it always fails and the kernel message
prints out:

Error: Driver 'configfs-gadget' is already registered, aborting...
UDC core: g1: driver registration failed: -16

This commit fixes the problem by a ".N" suffix added to each
configfs_gadget's driver name (where N is a unique ID number),
thus making the names distinct.

Fixes: fc274c1e9973 ("USB: gadget: Add a new bus for gadgets")
Signed-off-by: Chanh Nguyen <chanh@xxxxxxxxxxxxxxxxxxxxxx>

---
Changes in v2:
  - Replace scnprintf() by kasprintf() to simplify the code [CJ]
  - Move the clean up code from gadgets_drop() to
    gadget_info_attr_release()                        [Frank Li]
  - Correct the resource free up in gadges_make()   [Alan Stern]
  - Remove the unnecessary variable in gadgets_make()    [Chanh]
  - Fixes minor grammar issue in commit message          [Chanh]
---
 drivers/usb/gadget/configfs.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c
index 96121d1c8df4..7faf68bfa716 100644
--- a/drivers/usb/gadget/configfs.c
+++ b/drivers/usb/gadget/configfs.c
@@ -3,6 +3,7 @@
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/device.h>
+#include <linux/idr.h>
 #include <linux/kstrtox.h>
 #include <linux/nls.h>
 #include <linux/usb/composite.h>
@@ -11,6 +12,8 @@
 #include "u_f.h"
 #include "u_os_desc.h"
 
+static DEFINE_IDA(driver_id_numbers);
+
 int check_user_usb_string(const char *name,
 		struct usb_gadget_strings *stringtab_dev)
 {
@@ -52,6 +55,9 @@ struct gadget_info {
 	char qw_sign[OS_STRING_QW_SIGN_LEN];
 	spinlock_t spinlock;
 	bool unbind;
+
+	/* Make driver names unique */
+	int driver_id_number;
 };
 
 static inline struct gadget_info *to_gadget_info(struct config_item *item)
@@ -393,6 +399,8 @@ static void gadget_info_attr_release(struct config_item *item)
 	WARN_ON(!list_empty(&gi->string_list));
 	WARN_ON(!list_empty(&gi->available_func));
 	kfree(gi->composite.gadget_driver.function);
+	kfree(gi->composite.gadget_driver.driver.name);
+	ida_free(&driver_id_numbers, gi->driver_id_number);
 	kfree(gi);
 }
 
@@ -1623,13 +1631,28 @@ static struct config_group *gadgets_make(
 
 	gi->composite.gadget_driver = configfs_driver_template;
 
+	gi->driver_id_number = ida_alloc(&driver_id_numbers, GFP_KERNEL);
+	if (gi->driver_id_number < 0)
+		goto err;
+
+	gi->composite.gadget_driver.driver.name = kasprintf(GFP_KERNEL,
+							    "configfs-gadget.%d",
+							    gi->driver_id_number);
+	if (!gi->composite.gadget_driver.driver.name)
+		goto out_free_driver_id_number;
+
 	gi->composite.gadget_driver.function = kstrdup(name, GFP_KERNEL);
 	gi->composite.name = gi->composite.gadget_driver.function;
 
 	if (!gi->composite.gadget_driver.function)
-		goto err;
+		goto out_free_driver_name;
 
 	return &gi->group;
+
+out_free_driver_name:
+	kfree(gi->composite.gadget_driver.driver.name);
+out_free_driver_id_number:
+	ida_free(&driver_id_numbers, gi->driver_id_number);
 err:
 	kfree(gi);
 	return ERR_PTR(-ENOMEM);
-- 
2.17.1