Re: [Qemu-devel] [PATCH] [slirp] Make ARP replies at least 64 bytes long

["Hervé Poussineau" <hpoussin@reactos.org>]

Edgar E. Iglesias a écrit :
> On Mon, Sep 13, 2010 at 11:02:42PM +0200, Hervé Poussineau wrote:
>   
>> IEEE 802.3 standard requires Ethernet frames to be at least 64 bytes long.
>> If it is not the case, they will be considered as runt frames, and may be ignored by netcard and/or OS
>>
>> Signed-off-by: Hervé Poussineau <hpoussin@reactos.org>
>> ---
>>  slirp/slirp.c |   12 ++++++++----
>>  1 files changed, 8 insertions(+), 4 deletions(-)
>>
>> diff --git a/slirp/slirp.c b/slirp/slirp.c
>> index 82fd9b4..2e8c017 100644
>> --- a/slirp/slirp.c
>> +++ b/slirp/slirp.c
>> @@ -599,9 +599,12 @@ static void arp_input(Slirp *slirp, const uint8_t *pkt, int pkt_len)
>>  {
>>      struct ethhdr *eh = (struct ethhdr *)pkt;
>>      struct arphdr *ah = (struct arphdr *)(pkt + ETH_HLEN);
>> -    uint8_t arp_reply[ETH_HLEN + sizeof(struct arphdr)];
>> -    struct ethhdr *reh = (struct ethhdr *)arp_reply;
>> -    struct arphdr *rah = (struct arphdr *)(arp_reply + ETH_HLEN);
>> +    union {
>> +        uint8_t data[ETH_HLEN + sizeof(struct arphdr)];
>> +        uint8_t payload[64]; /* Minimum Ethernet frame size */
>> +    } arp_reply;
>> +    struct ethhdr *reh = (struct ethhdr *)arp_reply.data;
>> +    struct arphdr *rah = (struct arphdr *)(arp_reply.data + ETH_HLEN);
>>     
>
>
> Hi,
>
> Would you mind explaning the point of the union here? Why not just
> do something like:
>
> -    uint8_t arp_reply[ETH_HLEN + sizeof(struct arphdr)];
> +    uint8_t arp_reply[MAX(ETH_HLEN + sizeof(struct arphdr), 64)];
>
>   
Good idea. I'll send an updated patch soon.

Hervé