Re: [PATCH 09/17] Move unicode to ASCII conversion to sharedfunction.

[Adam Borowski]

On Mon, Sep 16, 2013 at 09:11:25PM -0700, Roy Franz wrote:
> +/* Convert the unicode UEFI command line to ASCII to pass to kernel.
> + * Size of memory allocated return in *cmd_line_len.
> + * Returns NULL on error.
> + */
> +static char *efi_convert_cmdline_to_ascii(efi_system_table_t *sys_table_arg,

> +       int load_options_size = image->load_options_size / 2; /* ASCII */

> +	for (i = 0; i < options_size - 1; i++)
> +		*s1++ = *s2++;

I'm afraid both this commit and comments inside are misnamed.  What you're
changing here is the encoding rather than character set.

In fact, these days it's 8-bit encodings that are more likely to be Unicode
than 16-bit ones: UTF-8 is ubiquitous, while you usually get UCS2 at most.
In either case, though, we have here is a 7-bit charset encoded as either
8-bit or 16-bit units.  What this function does is blindly truncating upper
byte.  The supported payload is in both cases ASCII.

I'd thus rename the function to what it already does: truncating u16 to u8,
and adjust comments accordingly.

Replacing values above 126 with a token character like '?' would be good
too: that'd avoid producing corrupted characters and/or random ASCII chars.

Your commit only moves things around, so it might be out of scope for now,
but I wonder: what if the kernel actually supported Unicode here?  Few
cmdline arguments take values where non-ASCII makes sense, but at least some
do: for example, a Russian guy is not unlikely to name subvolumes using
cyrillic.  Supporting that would be easy (estimating the length then
utf16s_to_utf8s()).  There's just one problem: which encoding to use, but
these days, most distributions have either dropped non-UTF8 or hardly pay
lip service, so we could get away with hard-coding UTF-8: those few who
use ancient charsets can stick to ASCII.  Would this be ok?  If so, shout,
I can code this if you don't care enough.

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