Re: [PATCH 1/5] Fix IPv6 zero-run compression.

[Tu Dinh <ngoc-tu.dinh@xxxxxxxxxx>]

On 10/09/2026 14:54, Owen Smith wrote:
> ZeroIndex was only set when the first zero was found, and ZeroCount is set to
> the longest run of zeros. This would incorrectly compress an address with
> a two runs of zeros, e.g. "1:0:0:2:0:0:0:3" to "1::0:0:0:3".
> ZeroIndex should be recalculated whenever a longer run of zeros is detected,
> so that the above run is correctly compressed to "1:0:2::3"
> 
> Simplifies the condition detecting an ending zero run, as Index would always
> be 7 when a trailing ":" is required.
> 
> Assisted-by: ClaudeCode:claude-opus-4.8
> Signed-off-by: Owen Smith <owen.smith@xxxxxxxxxx>

Hello,

RFC4291#2.2 [1] mandates that the "::" can only appear once in an 
address. If there are more than one "::", the address will become ambiguous.

[1] https://datatracker.ietf.org/doc/html/rfc4291#section-2.2
> ---
>   src/xenvif/frontend.c | 9 ++++-----
>   1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/src/xenvif/frontend.c b/src/xenvif/frontend.c
> index bece661..56fcc30 100644
> --- a/src/xenvif/frontend.c
> +++ b/src/xenvif/frontend.c
> @@ -774,22 +774,21 @@ FrontendDumpIPv6Address(
>               Count = 0;
>   
>           if (Count > ZeroCount) {
> -            if (Count == 1)
> -                ZeroIndex = Index;
> +            ZeroIndex = 1 + Index - Count;
>               ZeroCount = Count;
>           }
>       }
>   
>       if (ZeroCount > 1) {
> -        CHAR                        Parts[8][sizeof(":XXXX")];
> +        CHAR                        Parts[8][sizeof(":XXXX")] = { 0 };
>   
>           for (Index = 0; Index < 8; Index++) {
>               // Consecutive 0s are collapsed into a single semicolon, so that
>               // appending :xxxx segments would work naturally.
>               // Compensate for the missing appended semicolon if the last 
> word
>               // was also collapsed.
> -            if (Index == ZeroIndex || (Index == 7 &&
> -                                       Index == ZeroIndex + ZeroCount - 1)) {
> +            if (Index == ZeroIndex ||
> +                (Index == 7 && ZeroIndex + ZeroCount == 8)) {
>                   Parts[Index][0] = ':';
>                   Parts[Index][1] = '\0';
>               } else if (Index > ZeroIndex && Index < ZeroIndex + ZeroCount) {



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