linux-kernel - Re: [PATCH] usb: gadget: don't create new string

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Message-id: <544F95C3.2080306@samsung.com>
Date:	Tue, 28 Oct 2014 14:10:27 +0100
From:	Andrzej Pietrasiewicz <andrzej.p@...sung.com>
To:	Neil Zhang <zhangwm@...vell.com>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc:	balbi@...com, gregkh@...uxfoundation.org
Subject: Re: [PATCH] usb: gadget: don't create new string_container if already
 exist

Hi,

W dniu 28.10.2014 o 12:33, Neil Zhang pisze:
> Don't create new usb_gadget_string_container if the current strings are
> already exist in the usb_composite_dev.
> Otherwise the ids_tab will overflow soon if we bind / unbind usb
> functions frequently like android does.

The problem you are describing does not exist in mainline kernel,
where functions are always unbound as part of the whole gadget's
unbind - regardless of whether it is a legacy gadget or configfs-composed
gadget. When the whole gadget is unbound, composite_dev_cleanup()
is called which zeroes cdev->next_string_id and frees all gadget
strings containers.

>
> Signed-off-by: Neil Zhang <zhangwm@...vell.com>
> ---
>   drivers/usb/gadget/composite.c |    6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
> index a8c18df..6fe3c6b 100644
> --- a/drivers/usb/gadget/composite.c
> +++ b/drivers/usb/gadget/composite.c
> @@ -1183,6 +1183,12 @@ struct usb_string *usb_gstrings_attach(struct usb_composite_dev *cdev,
>   	if (!n_gstrings)
>   		return ERR_PTR(-EINVAL);
>
> +	list_for_each_entry(uc, &cdev->gstrings, list) {
> +		n_gs = get_containers_gs(uc);
> +		if (!strcmp(n_gs[0]->strings[0].s, sp[0]->strings[0].s))

To me it looks like it is a big assumption that if the first string matches,
the rest are the same, too. Isn't it?

Anyway, this solution looks more like pushing the moment when cdev->next_string_id
becomes 254 to a later time rather than preventing such a situation.

If usb_gstrings_attach() happens at function bind time, perhaps there
should be some usb_gstrings_detach() called at function unbind?

AP

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