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Date: Fri, 19 Oct 2012 13:36:37 +0200
From: Daniel Borkmann <danborkmann@...earbox.net>
To: Paul Chavent <Paul.Chavent@...ra.fr>
Cc: davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] packet mmap : allow the user to choose tx data offset.
On Fri, Oct 19, 2012 at 9:21 AM, Paul Chavent <Paul.Chavent@...ra.fr> wrote:
> The tx data offset of packet mmap tx ring used to be :
> (TPACKET2_HDRLEN - sizeof(struct sockaddr_ll))
>
> The problem is that, with SOCK_RAW socket, the payload
> (14 bytes after the begening of the user data) is misaligned.
>
> This patch allow to let the user give an offset for it's tx
> data if he desires.
>
> Set sock option PACKET_TX_HAS_OFF to 1, then specify in each
> frame of your tx ring tp_net for SOCK_DGRAM, or tp_mac for
> SOCK_RAW.
>
> Signed-off-by: Paul Chavent <paul.chavent@...ra.fr>
> ---
> Documentation/networking/packet_mmap.txt | 13 +++++++++
> include/uapi/linux/if_packet.h | 1 +
> net/packet/af_packet.c | 48 +++++++++++++++++++++++++++++++-
> net/packet/internal.h | 1 +
> 4 files changed, 62 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/networking/packet_mmap.txt b/Documentation/networking/packet_mmap.txt
> index 1c08a4b..c805e5f 100644
> --- a/Documentation/networking/packet_mmap.txt
> +++ b/Documentation/networking/packet_mmap.txt
> @@ -163,6 +163,19 @@ As capture, each frame contains two parts:
>
> A complete tutorial is available at: http://wiki.gnu-log.net/
>
> +By default, the user should put data at :
> + frame base + TPACKET_HDRLEN - sizeof(struct sockaddr_ll)
TPACKET_HDRLEN is only for tpacket, version 1. Maybe you should mention that.
> +So, whatever you choose for the socket mode (SOCK_DGRAM or SOCK_RAW),
> +the begening of the user data will be at :
Typo in "begening".
> + frame base + TPACKET_ALIGN(sizeof(struct tpacket_hdr))
See above, tpacket, version 1.
> +If you whish to put user data at a custom offset from the begenning of
Typo in "whish" and "begenning".
> +the frame (for payload alignment with SOCK_RAW mode for instance) you
> +can set tp_net (with SOCK_DGRAM) or tp_mac (with SOCK_RAW). In order
> +to make this work it must be enabled previously with setsockopt()
> +and the PACKET_TX_HAS_OFF option.
> +
> --------------------------------------------------------------------------------
> + PACKET_MMAP settings
> --------------------------------------------------------------------------------
> diff --git a/include/uapi/linux/if_packet.h b/include/uapi/linux/if_packet.h
> index f379929..f9a6037 100644
> --- a/include/uapi/linux/if_packet.h
> +++ b/include/uapi/linux/if_packet.h
> @@ -50,6 +50,7 @@ struct sockaddr_ll {
> #define PACKET_TX_TIMESTAMP 16
> #define PACKET_TIMESTAMP 17
> #define PACKET_FANOUT 18
> +#define PACKET_TX_HAS_OFF 19
>
> #define PACKET_FANOUT_HASH 0
> #define PACKET_FANOUT_LB 1
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index 94060ed..b6df577 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -1881,7 +1881,37 @@ static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
> skb_reserve(skb, hlen);
> skb_reset_network_header(skb);
>
> - data = ph.raw + po->tp_hdrlen - sizeof(struct sockaddr_ll);
> + if (po->tp_tx_has_off) {
> + int off_min = po->tp_hdrlen - sizeof(struct sockaddr_ll);
> + int off_max = po->tx_ring.frame_size - tp_len;
I think here, the header length is missing as well. Have you tested
this with min/max offsets?
Maybe it is more reasonable to put off = off_min at the beginning and
then add tp_mac to it. Thus, tp_mac can also be 0 with
PACKET_TX_HAS_OFF.
> + int off;
For offsets, better use off_t, or here u32. Also, add a newline after
variable declaration.
> + if (sock->type != SOCK_DGRAM)
Why not test for == SOCK_RAW? This makes it more readable.
> + switch (po->tp_version) {
> + case TPACKET_V2:
> + off = ph.h2->tp_mac;
> + break;
> + default:
> + off = ph.h1->tp_mac;
TPACKET_V1 as default is wrong since there's also TPACKET_V3. What
about TPACKET_V3 in general in your patch? You simply ignore it.
> + break;
> + }
> + else
> + switch (po->tp_version) {
> + case TPACKET_V2:
> + off = ph.h2->tp_net;
> + break;
> + default:
> + off = ph.h1->tp_net;
> + break;
> + }
Same as above. You should also put braces around the if-else
construct. Sure, it's only one statement after that, but this spans
across multiple lines and can make it error-prone in future changes.
> + if (unlikely((off < off_min) || (off_max < off))) {
> + pr_err("payload offset (%d) out of range [%d;%d]\n",
> + off, off_min, off_max);
> + return -EINVAL;
> + }
if you set off initially to off_min, you could drop the check for off < off_min.
> + data = ph.raw + off;
> + } else {
> + data = ph.raw + po->tp_hdrlen - sizeof(struct sockaddr_ll);
> + }
> to_write = tp_len;
>
> if (sock->type == SOCK_DGRAM) {
> @@ -3111,6 +3141,19 @@ packet_setsockopt(struct socket *sock, int level, int optname, char __user *optv
>
> return fanout_add(sk, val & 0xffff, val >> 16);
> }
> + case PACKET_TX_HAS_OFF:
> + {
> + unsigned int val;
> +
> + if (optlen != sizeof(val))
> + return -EINVAL;
> + if (po->rx_ring.pg_vec || po->tx_ring.pg_vec)
> + return -EBUSY;
> + if (copy_from_user(&val, optval, sizeof(val)))
> + return -EFAULT;
> + po->tp_tx_has_off = !!val;
> + return 0;
> + }
> default:
> return -ENOPROTOOPT;
> }
> @@ -3202,6 +3245,9 @@ static int packet_getsockopt(struct socket *sock, int level, int optname,
> ((u32)po->fanout->type << 16)) :
> 0);
> break;
> + case PACKET_TX_HAS_OFF:
> + val = po->tp_tx_has_off;
> + break;
> default:
> return -ENOPROTOOPT;
> }
> diff --git a/net/packet/internal.h b/net/packet/internal.h
> index 44945f6..169e60d 100644
> --- a/net/packet/internal.h
> +++ b/net/packet/internal.h
> @@ -110,6 +110,7 @@ struct packet_sock {
> unsigned int tp_reserve;
> unsigned int tp_loss:1;
> unsigned int tp_tstamp;
> + unsigned int tp_tx_has_off:1;
> struct packet_type prot_hook ____cacheline_aligned_in_smp;
> };
--
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