Re: [PATCH]console:UTF-8 mode compatibility fixes

[Andrew Morton <akpm@osdl.org>]

Adam Tla/lka <atlka@pg.gda.pl> wrote:
>
> 
> This patch applies to 2.6.15.3 kernel sources to drivers/char/vt.c file.
> It should work with other versions too.
> 
> Changed console behaviour so in UTF-8 mode vt100 alternate character
> sequences work as described in terminfo/termcap linux terminal definition.
> Programs can use vt100 control seqences - smacs, rmacs and acsc  characters
> in UTF-8 mode in the same way as in normal mode so one definition is always
> valid - current behaviour make these seqences not working in UTF-8 mode.
> 
> Added reporting malformed UTF-8 seqences as replacement glyphs.
> I think that terminal should always display something rather then ignoring
> these kind of data as it does now. Also it sticks to Unicode standards
> saying that every wrong byte should be reported. It is more human readable
> too in case of Latin subsets including ASCII chars.
> 
> ...
>
> -		} else if (vc->vc_utf) {
> +		} else if (vc->vc_utf && !vc->vc_disp_ctrl) {
>  		    /* Combine UTF-8 into Unicode */
> -		    /* Incomplete characters silently ignored */
> +		    /* Malformed sequence represented as replacement glyphs */
> +rescan_last_byte:
>  		    if(c > 0x7f) {
>
> ...
>
> +					if (vc->vc_npar) {
> +						c = orig;
> +						goto rescan_last_byte;
> +					}
>
> ...
>
> +				}
> +				vc->vc_utf_count = 0;
> +				c = orig;
> +				goto rescan_last_byte;
> +			}
>  			continue;
>  		}

I spent some time trying to work out why this cannot cause an infinite loop
and gave up.  Can you explain?