Unicode USB strings conversion

Nick Hibma nick at van-laarhoven.org
Tue Nov 18 23:55:15 PST 2008

In the USB code (and I bet it is the same in the USB4BSD code) unicode 
characters in strings are converted in a very crude way to ASCII. As I have 
a user on the line who sees rubbish in his logs and when using 
usbctl/usbdevs/etc., I bet this is the problem.

I'd like to try and fix this problem by using libkern/libiconv.

1) Is this the right approach to convert UTF8 to printable string in  the 

2) Is this needed at all in the short term future? I remember seeing 
attempts at making the kernel use UTF8.

3) Does anyone know of a good example in the code without me having to hunt 
through the kernel to find it?

For reference: The code that needs replacing is:


        s = buf;
        n = size / 2 - 1;
        for (i = 0; i < n && i < len - 1; i++) {
                c = UGETW(us.bString[i]);
                /* Convert from Unicode, handle buggy strings. */
                if ((c & 0xff00) == 0)
                        *s++ = c;
                else if ((c & 0x00ff) == 0 && swap)
                        *s++ = c >> 8;
                        *s++ = '?';
        *s++ = 0;

I haven't got the USB specs handy, but I believe that this is a simple way 
of converting LE and BE UTF8 to ASCII.


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