linux-kernel - Re: [PATCH] USB: gadget: Add ID numbers to configfs-gadget driver names

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Message-ID: <720b814d-5102-04d3-4938-33a25e87a46d@wanadoo.fr>
Date:   Tue, 13 Dec 2022 08:22:24 +0100
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Chanh Nguyen <chanh@...amperecomputing.com>
Cc:     OpenBMC Maillist <openbmc@...ts.ozlabs.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dan Vacura <w36195@...orola.com>,
        Jakob Koschel <jakobkoschel@...il.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Vijayavardhan Vennapusa <vvreddy@...eaurora.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Open Source Submission <patches@...erecomputing.com>
Subject: Re: [PATCH] USB: gadget: Add ID numbers to configfs-gadget driver
 names

Le 13/12/2022 à 05:12, Chanh Nguyen a écrit :
> 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-shex6MNQR2J/SfDzf78azzKzEDxYleXD@...lic.gmane.org>
> ---
>   drivers/usb/gadget/configfs.c | 42 +++++++++++++++++++++++++++++++++++
>   1 file changed, 42 insertions(+)
> 
> diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c
> index 96121d1c8df4..d8c5156ad777 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 +12,16 @@
>   #include "u_f.h"
>   #include "u_os_desc.h"
>   
> +static DEFINE_IDA(driver_id_numbers);
> +
> +/*
> + * Driver name has the form of "configfs-gadget.%d", where %d
> + * is id allocated by ida_alloc(). The max value returns by
> + * ida_alloc() is INT_MAX, in 64-bit system, it is about nine
> + * quintillion: 19 digits in decimal. Set the max length to 35.
> + */
> +#define DRIVER_NAME_LENGTH_MAX 35

Hi,

if paranoiac, the final \0 seems to be missing in the max length 
computation, but see below.

> +
>   int check_user_usb_string(const char *name,
>   		struct usb_gadget_strings *stringtab_dev)
>   {
> @@ -52,6 +63,9 @@ 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)
> @@ -1582,6 +1596,8 @@ static struct config_group *gadgets_make(
>   		const char *name)
>   {
>   	struct gadget_info *gi;
> +	char *driver_name;
> +	int ret;
>   
>   	gi = kzalloc(sizeof(*gi), GFP_KERNEL);
>   	if (!gi)
> @@ -1623,6 +1639,21 @@ static struct config_group *gadgets_make(
>   
>   	gi->composite.gadget_driver = configfs_driver_template;
>   
> +	ret = ida_alloc(&driver_id_numbers, GFP_KERNEL);
> +	if (ret < 0)
> +		goto err;
> +	gi->driver_id_number = ret;
> +
> +	driver_name = kmalloc(DRIVER_NAME_LENGTH_MAX, GFP_KERNEL);
> +	if (!driver_name)
> +		goto out_free_driver_id_number;
> +
> +	ret = scnprintf(driver_name, DRIVER_NAME_LENGTH_MAX,
> +			"configfs-gadget.%d", gi->driver_id_number);


using kasprintf() looks simpler here.
No need to kmalloc()+scnprintf(), and no need for DRIVER_NAME_LENGTH_MAX.

Just my 2c,

CJ

> +	if (ret < 0)
> +		goto out_free_driver_name;
> +
> +	gi->composite.gadget_driver.driver.name = driver_name;
>   	gi->composite.gadget_driver.function = kstrdup(name, GFP_KERNEL);
>   	gi->composite.name = gi->composite.gadget_driver.function;
>   
> @@ -1630,6 +1661,11 @@ static struct config_group *gadgets_make(
>   		goto err;
>   
>   	return &gi->group;
> +
> +out_free_driver_name:
> +	kfree(driver_name);
> +out_free_driver_id_number:
> +	ida_free(&driver_id_numbers, gi->driver_id_number);
>   err:
>   	kfree(gi);
>   	return ERR_PTR(-ENOMEM);
> @@ -1637,6 +1673,12 @@ static struct config_group *gadgets_make(
>   
>   static void gadgets_drop(struct config_group *group, struct config_item *item)
>   {
> +	struct gadget_info *gi = to_gadget_info(item);
> +
> +	mutex_lock(&gi->lock);
> +	kfree(gi->composite.gadget_driver.driver.name);
> +	ida_free(&driver_id_numbers, gi->driver_id_number);
> +	mutex_unlock(&gi->lock);
>   	config_item_put(item);
>   }
>