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Message-ID: <d4ff2572-6fbf-cedd-9255-7411aadc09ad@antgroup.com>
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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