Hi,
Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> writes:
> On Thu, Feb 09, 2017 at 10:04:43AM -0800, Stefan Agner wrote:
>> 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.
>
> It's up to Felipe, give him a chance to catch up on patches...
I really don't know what to do here :-) Either way have the potential of
breaking userspace. Maybe returning UTF8 as in write is the lesser of
two evils.
--
balbi
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