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Date: Thu, 9 Feb 2023 09:45:01 -0500
From: Willem de Bruijn <willemb@...gle.com>
To: 沈安琪(凛玥) <amy.saq@...group.com>
Cc: netdev@...r.kernel.org, willemdebruijn.kernel@...il.com,
mst@...hat.com, davem@...emloft.net, jasowang@...hat.com,
谈鉴锋 <henry.tjf@...group.com>
Subject: Re: [PATCH 1/2] net/packet: add socketopt to set/get vnet_hdr_sz
On Thu, Feb 9, 2023 at 7:43 AM 沈安琪(凛玥) <amy.saq@...group.com> wrote:
>
> From: "Jianfeng Tan" <henry.tjf@...group.com>
>
> Raw socket can be used as the backend for kernel vhost, like tap.
Please refer to PF_PACKET sockets as packet sockets.
"raw" sockets is ambiguous: it is also used to refer to type SOCK_RAW
of other socket families.
> However, in current raw socket implementation, it use hardcoded virtio
> net header length, which will cause error mac header parsing when some
> virtio features that need virtio net header other than 10-byte are used.
This series only adds support for skipping past two extra bytes.
The 2-byte field num_buffers in virtio_net_hdr_mrg_rxbuf is used for
coalesced buffers. That is not a feature packet sockets support.
How do you intend to use this? Only ever with num_buffers == 1?
We have to make ABI changes sparingly. It would take another setsockopt
to signal actual use of this feature.
If adding an extended struct, then this also needs to be documented in
the UAPI headers.
> By adding extra field vnet_hdr_sz in packet_sock to record virtio net
> header size that current raw socket should use and supporting extra
> sockopt PACKET_VNET_HDR_SZ to allow user level set specified vnet header
> size to current socket, raw socket will know the exact virtio net header
> size it should use instead of hardcoding to avoid incorrect header
> parsing.
>
> Signed-off-by: Jianfeng Tan <henry.tjf@...group.com>
> Co-developed-by: Anqi Shen <amy.saq@...group.com>
> Signed-off-by: Anqi Shen <amy.saq@...group.com>
> ---
> include/uapi/linux/if_packet.h | 1 +
> net/packet/af_packet.c | 34 ++++++++++++++++++++++++++++++++++
> net/packet/internal.h | 3 ++-
> 3 files changed, 37 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/if_packet.h b/include/uapi/linux/if_packet.h
> index 78c981d..9efc423 100644
> --- a/include/uapi/linux/if_packet.h
> +++ b/include/uapi/linux/if_packet.h
> @@ -59,6 +59,7 @@ struct sockaddr_ll {
> #define PACKET_ROLLOVER_STATS 21
> #define PACKET_FANOUT_DATA 22
> #define PACKET_IGNORE_OUTGOING 23
> +#define PACKET_VNET_HDR_SZ 24
>
> #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 8ffb19c..8389f18 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -3936,11 +3936,42 @@ static void packet_flush_mclist(struct sock *sk)
> ret = -EBUSY;
> } else {
> po->has_vnet_hdr = !!val;
> + /* set vnet_hdr_sz to default value */
> + if (po->has_vnet_hdr)
> + po->vnet_hdr_sz = sizeof(struct virtio_net_hdr);
> + else
> + po->vnet_hdr_sz = 0;
> ret = 0;
> }
> release_sock(sk);
> return ret;
> }
> + case PACKET_VNET_HDR_SZ:
> + {
> + int val;
> +
> + if (sock->type != SOCK_RAW)
> + return -EINVAL;
> + if (optlen < sizeof(val))
> + return -EINVAL;
> + if (copy_from_user(&val, optval, sizeof(val)))
> + return -EFAULT;
This duplicates the code in PACKET_VNET_HR. I'd prefer:
case PACKET_VNET_HDR:
case PACKET_VNET_HDR_SZ:
.. sanity checks and copy from user ..
if (optname = PACKET_VNET_HDR)
val = sizeof(struct virtio_net_hdr);
And move the check for valid lengths before taking the lock.
> +
> + lock_sock(sk);
> + if (po->rx_ring.pg_vec || po->tx_ring.pg_vec) {
> + ret = -EBUSY;
> + } else {
> + if (val == sizeof(struct virtio_net_hdr) ||
> + val == sizeof(struct virtio_net_hdr_mrg_rxbuf)) {
> + po->vnet_hdr_sz = val;
> + ret = 0;
> + } else {
> + ret = -EINVAL;
> + }
> + }
> + release_sock(sk);
> + return ret;
> + }
> case PACKET_TIMESTAMP:
> {
> int val;
> @@ -4070,6 +4101,9 @@ static int packet_getsockopt(struct socket *sock, int level, int optname,
> case PACKET_VNET_HDR:
> val = po->has_vnet_hdr;
> break;
> + case PACKET_VNET_HDR_SZ:
> + val = po->vnet_hdr_sz;
> + break;
> case PACKET_VERSION:
> val = po->tp_version;
> break;
> diff --git a/net/packet/internal.h b/net/packet/internal.h
> index 48af35b..e27b47d 100644
> --- a/net/packet/internal.h
> +++ b/net/packet/internal.h
> @@ -121,7 +121,8 @@ struct packet_sock {
> origdev:1,
> has_vnet_hdr:1,
> tp_loss:1,
> - tp_tx_has_off:1;
> + tp_tx_has_off:1,
> + vnet_hdr_sz:8; /* vnet header size should use */
This location looks fine from the point of view of using holes in the
struct:
/* --- cacheline 12 boundary (768 bytes) --- */
struct packet_ring_buffer rx_ring; /* 768 200 */
/* --- cacheline 15 boundary (960 bytes) was 8 bytes ago --- */
struct packet_ring_buffer tx_ring; /* 968 200 */
/* --- cacheline 18 boundary (1152 bytes) was 16 bytes ago --- */
int copy_thresh; /* 1168 4 */
spinlock_t bind_lock; /* 1172 4 */
struct mutex pg_vec_lock; /* 1176 32 */
unsigned int running; /* 1208 4 */
unsigned int auxdata:1; /* 1212: 0 4 */
unsigned int origdev:1; /* 1212: 1 4 */
unsigned int has_vnet_hdr:1; /* 1212: 2 4 */
unsigned int tp_loss:1; /* 1212: 3 4 */
unsigned int tp_tx_has_off:1; /* 1212: 4 4 */
/* XXX 27 bits hole, try to pack */
/* --- cacheline 19 boundary (1216 bytes) --- */
> int pressure;
> int ifindex; /* bound device */
> __be16 num;
> --
> 1.8.3.1
>
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