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.
--
Stefan
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