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Date: Sat, 18 Jun 2011 07:54:33 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: greearb@...delatech.com
Cc: netdev@...r.kernel.org
Subject: Re: [RFC 4/5] net: Support sending frame with specified FCS.
Le vendredi 17 juin 2011 à 17:09 -0700, greearb@...delatech.com a
écrit :
> From: Ben Greear <greearb@...delatech.com>
>
> This allows user-space to send a packet with the
> ethernet FCS appended to the end. Supporting NICs
> will know to disable their own FCS calculations and
> send frame as is.
>
> This is useful for injecting bad frames on a network
> for testing.
>
> Signed-off-by: Ben Greear <greearb@...delatech.com>
> ---
> :100644 100644 9a6115e... 22193a2... M include/asm-generic/socket.h
> :100644 100644 c0a4f3a... 05b15be... M include/linux/skbuff.h
> :100644 100644 f2046e4... d7e0d88... M include/net/sock.h
> :100644 100644 46cbd28... a552560... M net/core/skbuff.c
> :100644 100644 6e81978... 0c5f827... M net/core/sock.c
> :100644 100644 c0c3cda... 0d29d68... M net/packet/af_packet.c
> include/asm-generic/socket.h | 7 +++++++
> include/linux/skbuff.h | 5 ++++-
> include/net/sock.h | 6 ++++++
> net/core/skbuff.c | 1 +
> net/core/sock.c | 7 +++++++
> net/packet/af_packet.c | 22 ++++++++++++++++++++--
> 6 files changed, 45 insertions(+), 3 deletions(-)
>
> diff --git a/include/asm-generic/socket.h b/include/asm-generic/socket.h
> index 9a6115e..22193a2 100644
> --- a/include/asm-generic/socket.h
> +++ b/include/asm-generic/socket.h
> @@ -64,4 +64,11 @@
> #define SO_DOMAIN 39
>
> #define SO_RXQ_OVFL 40
> +
> +/* Instruct lower device to not calculate the frame
> + * checksum. Useful for generating Ethernet frames
> + * with custom checksums.
> + */
> +#define SO_NOFCS 41
> +
Please take a look at :
arch/*/include/asm/socket.h for many arches.
> #endif /* __ASM_GENERIC_SOCKET_H */
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index c0a4f3a..05b15be 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -307,6 +307,8 @@ typedef unsigned char *sk_buff_data_t;
> * @peeked: this packet has been seen already, so stats have been
> * done for it, don't do them again
> * @nf_trace: netfilter packet trace flag
> + * @use_specified_ether_crc: skb is Ethernet frame with FCS already
> + * appended. Use that FCS. Requires special support in NIC.
> * @nfctinfo: Relationship of this skb to the connection
> * @nfct_reasm: netfilter conntrack re-assembly pointer
> * @nf_bridge: Saved data about a bridged frame - see br_netfilter.c
> @@ -396,7 +398,8 @@ struct sk_buff {
> #ifdef CONFIG_IPV6_NDISC_NODETYPE
> __u8 ndisc_nodetype:2;
> #endif
> - __u8 ooo_okay:1;
> + __u8 ooo_okay:1,
> + use_specified_ether_crc:1;
> kmemcheck_bitfield_end(flags2);
>
> /* 0/13 bit hole */
> diff --git a/include/net/sock.h b/include/net/sock.h
> index f2046e4..d7e0d88 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -563,6 +563,12 @@ enum sock_flags {
> SOCK_TIMESTAMPING_SYS_HARDWARE, /* %SOF_TIMESTAMPING_SYS_HARDWARE */
> SOCK_FASYNC, /* fasync() active */
> SOCK_RXQ_OVFL,
> + SOCK_DONT_DO_LL_FCS, /* Tell NIC not to do the Ethernet FCS.
> + * Will use last 4 bytes of packet sent from
> + * user-space instead. Requires special
> + * support in NIC.
> + */
> +
> };
>
> static inline void sock_copy_flags(struct sock *nsk, struct sock *osk)
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 46cbd28..a552560 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -541,6 +541,7 @@ static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
> new->tc_verd = old->tc_verd;
> #endif
> #endif
> + new->use_specified_ether_crc = old->use_specified_ether_crc;
> new->vlan_tci = old->vlan_tci;
>
> skb_copy_secmark(new, old);
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 6e81978..0c5f827 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -641,6 +641,13 @@ set_rcvbuf:
> sock_warn_obsolete_bsdism("setsockopt");
> break;
>
> + case SO_NOFCS:
> + if (valbool)
> + sk->sk_flags |= SOCK_DONT_DO_LL_FCS;
> + else
> + sk->sk_flags &= ~(SOCK_DONT_DO_LL_FCS);
> + break;
> +
> case SO_PASSCRED:
> if (valbool)
> set_bit(SOCK_PASSCRED, &sock->flags);
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index c0c3cda..0d29d68 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -430,6 +430,10 @@ static int packet_sendmsg_spkt(struct kiocb *iocb, struct socket *sock,
> struct net_device *dev;
> __be16 proto = 0;
> int err;
> + int kludge = 0;
> +
> + if (unlikely(sk->sk_flags & SOCK_DONT_DO_LL_FCS))
> + kludge = 4; /* We're doing our own FCS */
>
> /*
> * Get and verify the address.
> @@ -465,7 +469,7 @@ retry:
> */
>
> err = -EMSGSIZE;
> - if (len > dev->mtu + dev->hard_header_len + VLAN_HLEN)
> + if (len > dev->mtu + dev->hard_header_len + VLAN_HLEN + kludge)
> goto out_unlock;
>
> if (!skb) {
> @@ -518,6 +522,11 @@ retry:
> if (err < 0)
> goto out_unlock;
>
> + if (unlikely(sk->sk_flags & SOCK_DONT_DO_LL_FCS))
> + skb->use_specified_ether_crc = 1;
> + else
> + skb->use_specified_ether_crc = 0;
> +
Manipulating a bit field is very expensive, and having an else branch is
expensive as well, so please avoid setting crc to zero if its already
guaranteed to be so.
Also I cant see where you actually _set_ the fcs value : that might
trigger a kmemcheck warning later when we read it.
> dev_queue_xmit(skb);
> rcu_read_unlock();
> return len;
> @@ -1134,6 +1143,10 @@ static int packet_snd(struct socket *sock,
> int vnet_hdr_len;
> struct packet_sock *po = pkt_sk(sk);
> unsigned short gso_type = 0;
> + int kludge = 0;
> +
> + if (unlikely(sk->sk_flags & SOCK_DONT_DO_LL_FCS))
> + kludge = 4; /* We're doing our own Ethernet FCS */
kludge ? You mean fcs_len or something ? ;)
>
> /*
> * Get and verify the address.
> @@ -1215,7 +1228,7 @@ static int packet_snd(struct socket *sock,
> }
>
> err = -EMSGSIZE;
> - if (!gso_type && (len > dev->mtu + reserve + VLAN_HLEN))
> + if (!gso_type && (len > dev->mtu + reserve + VLAN_HLEN + kludge))
> goto out_unlock;
>
> err = -ENOBUFS;
> @@ -1278,6 +1291,11 @@ static int packet_snd(struct socket *sock,
> len += vnet_hdr_len;
> }
>
> + if (unlikely(sk->sk_flags & SOCK_DONT_DO_LL_FCS))
> + skb->use_specified_ether_crc = 1;
> + else
> + skb->use_specified_ether_crc = 0;
same remark here : ether_crc is already 0 here.
> +
> /*
> * Now send it
> */
--
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