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Date: Fri, 10 Feb 2023 12:00:10 +0800
From: "沈安琪(凛玥)" <amy.saq@...group.com>
To: Willem de Bruijn <willemb@...gle.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
在 2023/2/9 下午10:45, Willem de Bruijn 写道:
> 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?
This 2-byte field will later be used to record how many buffers it can
use when virtio mergeable is enable in drivers/vhost/net.c:1231.
Here we need to skip this 2-byte field in af_packet since otherwise, the
number of buffers info will overwrite the mac header info.
>
> 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.
Thanks for pointing out. It makes sense and we will address in the next
version of patch.
>
>> +
>> + 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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