linux-kernel - Re: [PATCH v2 2/4] usb: gadget: mass_storage: Store lun_opts in fsg

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Date:	Wed, 8 Apr 2015 10:15:32 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Krzysztof Opasiak <k.opasiak@...sung.com>
cc:	balbi@...com, <gregkh@...uxfoundation.org>, <jlbec@...lplan.org>,
	<andrzej.p@...sung.com>, <m.szyprowski@...sung.com>,
	<linux-api@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-usb@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] usb: gadget: mass_storage: Store lun_opts in
 fsg_opts

On Wed, 8 Apr 2015, Krzysztof Opasiak wrote:

> Signed-off-by: Krzysztof Opasiak <k.opasiak@...sung.com>
> ---
>  drivers/usb/gadget/function/f_mass_storage.c |    5 +++++
>  drivers/usb/gadget/function/f_mass_storage.h |    1 +
>  2 files changed, 6 insertions(+)
> 
> diff --git a/drivers/usb/gadget/function/f_mass_storage.c b/drivers/usb/gadget/function/f_mass_storage.c
> index 811929c..095b618 100644
> --- a/drivers/usb/gadget/function/f_mass_storage.c
> +++ b/drivers/usb/gadget/function/f_mass_storage.c
> @@ -3372,6 +3372,8 @@ static struct config_group *fsg_lun_make(struct config_group *group,
>  	}
>  	opts->lun = fsg_opts->common->luns[num];
>  	opts->lun_id = num;
> +	BUG_ON(fsg_opts->lun_opts[num]);

This is not a good idea.  BUG_ON should hardly ever be used.  In fact,
Linus has said that the only time BUG_ON should be used is when things
are so badly messed up that it is better to crash the computer than to
let it continue.

What's wrong with using WARN_ON instead?

> diff --git a/drivers/usb/gadget/function/f_mass_storage.h b/drivers/usb/gadget/function/f_mass_storage.h
> index b4866fc..0a7c656 100644
> --- a/drivers/usb/gadget/function/f_mass_storage.h
> +++ b/drivers/usb/gadget/function/f_mass_storage.h
> @@ -81,6 +81,7 @@ struct fsg_opts {
>  	struct fsg_common *common;
>  	struct usb_function_instance func_inst;
>  	struct fsg_lun_opts lun0;
> +	struct fsg_lun_opts *lun_opts[FSG_MAX_LUNS];

This looks strange.  Why is the entry for LUN 0 duplicated?

Alan Stern

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