linux-kernel - Re: [PATCH 1/2] fs: configfs: make qw

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Date:   Thu, 09 Feb 2017 10:04:43 -0800
From:   Stefan Agner <stefan@...er.ch>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     balbi@...nel.org, andrzej.p@...sung.com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] fs: configfs: make qw_sign attribute symmetric

On 2017-02-01 08:59, Stefan Agner wrote:
> On 2017-02-01 00:06, Greg KH wrote:
>> On Tue, Jan 31, 2017 at 06:19:16PM -0800, Stefan Agner wrote:
>>> Currently qw_sign requires UTF-8 character to set, but returns UTF-16
>>> when read. This isn't obvious when simply using cat since the null
>>> characters are not visible, but hexdump unveils the true string:
>>>
>>>   # echo MSFT100 > os_desc/qw_sign
>>>   # hexdump -C os_desc/qw_sign
>>>   00000000  4d 00 53 00 46 00 54 00  31 00 30 00 30 00        |M.S.F.T.1.0.0.|
>>>
>>> Make qw_sign symmetric by returning an UTF-8 string too. Also follow
>>> common convention and add a new line at the end.
>>
>> Doesn't USB require that strings be in UTF-16?  So why have the kernel
>> convert them?
> 
> That is a discussion we should have had when the write side of this has
> been added:
> 
> static ssize_t os_desc_qw_sign_store(struct config_item *item, const
> char *page,
> 				     size_t len)
> {
> 	struct gadget_info *gi = os_desc_item_to_gadget_info(item);
> 	int res, l;
> 
> 	l = min((int)len, OS_STRING_QW_SIGN_LEN >> 1);
> 	if (page[l - 1] == '\n')
> 		--l;
> 
> 	mutex_lock(&gi->lock);
> 	res = utf8s_to_utf16s(page, l,
> 			      UTF16_LITTLE_ENDIAN, (wchar_t *) gi->qw_sign,
> 			      OS_STRING_QW_SIGN_LEN);
> 	if (res > 0)
> 		res = len;
> 	mutex_unlock(&gi->lock);
> 
> 	return res;
> }
> 
> 
> The store function is definitely already in use today, e.g. this script
> used for ev3dev:
> https://github.com/ev3dev/ev3-systemd/blob/ev3dev-jessie/scripts/ev3-usb.sh
> 
> Changing it to UTF-16 would break that script... So changing the store
> part is the lesser of two evils.
> 
> Regarding new line: Just following what other attributes are doing by
> using the GS_STRINGS_R macro.

Any comment on this? In my opinion especially this first patch really
fixes a bug and should get applied... I can remove the newline if
preferred.

--
Stefan