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Date: Wed, 15 Sep 2010 21:39:02 +0200
From: =?ISO-8859-1?Q?Herv=E9_Poussineau?= <hpoussin@reactos.org>
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Subject: Re: [Qemu-devel] [PATCH] [slirp] Make ARP replies at least 64 bytes
	long
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	<20100914222257.GB16690@laped.lan>
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To: "Edgar E. Iglesias" <edgar.iglesias@gmail.com>
Cc: =?ISO-8859-1?Q?Herv=E9_Poussineau?= <hpoussin@reactos.org>, qemu-devel@nongnu.org

Edgar E. Iglesias a =E9crit :
> On Mon, Sep 13, 2010 at 11:02:42PM +0200, Herv=E9 Poussineau wrote:
>  =20
>> IEEE 802.3 standard requires Ethernet frames to be at least 64 bytes l=
ong.
>> 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: Herv=E9 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 =3D (struct ethhdr *)pkt;
>>      struct arphdr *ah =3D (struct arphdr *)(pkt + ETH_HLEN);
>> -    uint8_t arp_reply[ETH_HLEN + sizeof(struct arphdr)];
>> -    struct ethhdr *reh =3D (struct ethhdr *)arp_reply;
>> -    struct arphdr *rah =3D (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 =3D (struct ethhdr *)arp_reply.data;
>> +    struct arphdr *rah =3D (struct arphdr *)(arp_reply.data + ETH_HLE=
N);
>>    =20
>
>
> 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)];
>
>  =20
Good idea. I'll send an updated patch soon.

Herv=E9