Subject: Re: [PATCH 3/5] VSOCK: support receive mergeable rx buffer in guest

From: jiangyiwen <[email-masked]>
Date: Tue, 6 Nov 2018 14:41:54 +0800

On 2018/11/6 12:00, Jason Wang wrote:
> 
> On 2018/11/5 下午3:47, jiangyiwen wrote:
>> Guest receive mergeable rx buffer, it can merge
>> scatter rx buffer into a big buffer and then copy
>> to user space.
>>
>> Signed-off-by: Yiwen Jiang <[email-masked]>
>> ---
>>   include/linux/virtio_vsock.h            |  9 ++++
>>   net/vmw_vsock/virtio_transport.c        | 75 +++++++++++++++++++++++++++++----
>>   net/vmw_vsock/virtio_transport_common.c | 59 ++++++++++++++++++++++----
>>   3 files changed, 127 insertions(+), 16 deletions(-)
>>
>> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
>> index da9e1fe..6be3cd7 100644
>> --- a/include/linux/virtio_vsock.h
>> +++ b/include/linux/virtio_vsock.h
>> @@ -13,6 +13,8 @@
>>   #define VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE    (1024 * 4)
>>   #define VIRTIO_VSOCK_MAX_BUF_SIZE        0xFFFFFFFFUL
>>   #define VIRTIO_VSOCK_MAX_PKT_BUF_SIZE        (1024 * 64)
>> +/* virtio_vsock_pkt + max_pkt_len(default MAX_PKT_BUF_SIZE) */
>> +#define VIRTIO_VSOCK_MAX_MRG_BUF_NUM ((VIRTIO_VSOCK_MAX_PKT_BUF_SIZE / PAGE_SIZE) + 1)
>>
>>   /* Virtio-vsock feature */
>>   #define VIRTIO_VSOCK_F_MRG_RXBUF 0 /* Host can merge receive buffers. */
>> @@ -48,6 +50,11 @@ struct virtio_vsock_sock {
>>       struct list_head rx_queue;
>>   };
>>
>> +struct virtio_vsock_mrg_rxbuf {
>> +    void *buf;
>> +    u32 len;
>> +};
>> +
>>   struct virtio_vsock_pkt {
>>       struct virtio_vsock_hdr    hdr;
>>       struct virtio_vsock_mrg_rxbuf_hdr mrg_rxbuf_hdr;
>> @@ -59,6 +66,8 @@ struct virtio_vsock_pkt {
>>       u32 len;
>>       u32 off;
>>       bool reply;
>> +    bool mergeable;
>> +    struct virtio_vsock_mrg_rxbuf mrg_rxbuf[VIRTIO_VSOCK_MAX_MRG_BUF_NUM];
>>   };
> 
> 
> It's better to use iov here I think, and drop buf completely.
> 
> And this is better to be done in an independent patch.
> 

You're right, I can use kvec instead of customized structure,
in addition, I don't understand about drop buf completely and
an independent patch.

Thanks.

> 
>>
>>   struct virtio_vsock_pkt_info {
>> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
>> index 2040a9e..3557ad3 100644
>> --- a/net/vmw_vsock/virtio_transport.c
>> +++ b/net/vmw_vsock/virtio_transport.c
>> @@ -359,11 +359,62 @@ static bool virtio_transport_more_replies(struct virtio_vsock *vsock)
>>       return val < virtqueue_get_vring_size(vq);
>>   }
>>
>> +static struct virtio_vsock_pkt *receive_mergeable(struct virtqueue *vq,
>> +        struct virtio_vsock *vsock, unsigned int *total_len)
>> +{
>> +    struct virtio_vsock_pkt *pkt;
>> +    u16 num_buf;
>> +    void *page;
>> +    unsigned int len;
>> +    int i = 0;
>> +
>> +    page = virtqueue_get_buf(vq, &len);
>> +    if (!page)
>> +        return NULL;
>> +
>> +    *total_len = len;
>> +    vsock->rx_buf_nr--;
>> +
>> +    pkt = page;
>> +    num_buf = le16_to_cpu(pkt->mrg_rxbuf_hdr.num_buffers);
>> +    if (!num_buf || num_buf > VIRTIO_VSOCK_MAX_MRG_BUF_NUM)
>> +        goto err;
>> +
>> +    pkt->mergeable = true;
>> +    if (!le32_to_cpu(pkt->hdr.len))
>> +        return pkt;
>> +
>> +    len -= sizeof(struct virtio_vsock_pkt);
>> +    pkt->mrg_rxbuf[i].buf = page + sizeof(struct virtio_vsock_pkt);
>> +    pkt->mrg_rxbuf[i].len = len;
>> +    i++;
>> +
>> +    while (--num_buf) {
>> +        page = virtqueue_get_buf(vq, &len);
>> +        if (!page)
>> +            goto err;
>> +
>> +        *total_len += len;
>> +        vsock->rx_buf_nr--;
>> +
>> +        pkt->mrg_rxbuf[i].buf = page;
>> +        pkt->mrg_rxbuf[i].len = len;
>> +        i++;
>> +    }
>> +
>> +    return pkt;
>> +err:
>> +    virtio_transport_free_pkt(pkt);
>> +    return NULL;
>> +}
> 
> 
> Similar logic could be found at virtio-net driver.
> 
> Haven't thought this deeply, but it looks to me use virtio-net driver is also possible, e.g for data-path, just register vsock specific callbacks.
> 
> 
>> +
>>   static void virtio_transport_rx_work(struct work_struct *work)
>>   {
>>       struct virtio_vsock *vsock =
>>           container_of(work, struct virtio_vsock, rx_work);
>>       struct virtqueue *vq;
>> +    size_t vsock_hlen = vsock->mergeable ? sizeof(struct virtio_vsock_pkt) :
>> +            sizeof(struct virtio_vsock_hdr);
>>
>>       vq = vsock->vqs[VSOCK_VQ_RX];
>>
>> @@ -383,21 +434,29 @@ static void virtio_transport_rx_work(struct work_struct *work)
>>                   goto out;
>>               }
>>
>> -            pkt = virtqueue_get_buf(vq, &len);
>> -            if (!pkt) {
>> -                break;
>> -            }
>> +            if (likely(vsock->mergeable)) {
>> +                pkt = receive_mergeable(vq, vsock, &len);
>> +                if (!pkt)
>> +                    break;
>>
>> -            vsock->rx_buf_nr--;
>> +                pkt->len = le32_to_cpu(pkt->hdr.len);
>> +            } else {
>> +                pkt = virtqueue_get_buf(vq, &len);
>> +                if (!pkt) {
>> +                    break;
>> +                }
>> +
>> +                vsock->rx_buf_nr--;
>> +            }
>>
>>               /* Drop short/long packets */
>> -            if (unlikely(len < sizeof(pkt->hdr) ||
>> -                     len > sizeof(pkt->hdr) + pkt->len)) {
>> +            if (unlikely(len < vsock_hlen ||
>> +                     len > vsock_hlen + pkt->len)) {
>>                   virtio_transport_free_pkt(pkt);
>>                   continue;
>>               }
>>
>> -            pkt->len = len - sizeof(pkt->hdr);
>> +            pkt->len = len - vsock_hlen;
>>               virtio_transport_deliver_tap_pkt(pkt);
>>               virtio_transport_recv_pkt(pkt);
>>           }
>> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>> index 3ae3a33..7bef1d5 100644
>> --- a/net/vmw_vsock/virtio_transport_common.c
>> +++ b/net/vmw_vsock/virtio_transport_common.c
>> @@ -272,14 +272,49 @@ static int virtio_transport_send_credit_update(struct vsock_sock *vsk,
>>            */
>>           spin_unlock_bh(&vvs->rx_lock);
>>
>> -        err = memcpy_to_msg(msg, pkt->buf + pkt->off, bytes);
>> -        if (err)
>> -            goto out;
>> +        if (pkt->mergeable) {
>> +            struct virtio_vsock_mrg_rxbuf *buf = pkt->mrg_rxbuf;
>> +            size_t mrg_copy_bytes, last_buf_total = 0, rxbuf_off;
>> +            size_t tmp_bytes = bytes;
>> +            int i;
>> +
>> +            for (i = 0; i < le16_to_cpu(pkt->mrg_rxbuf_hdr.num_buffers); i++) {
>> +                if (pkt->off > last_buf_total + buf[i].len) {
>> +                    last_buf_total += buf[i].len;
>> +                    continue;
>> +                }
>> +
>> +                rxbuf_off = pkt->off - last_buf_total;
>> +                mrg_copy_bytes = min(buf[i].len - rxbuf_off, tmp_bytes);
>> +                err = memcpy_to_msg(msg, buf[i].buf + rxbuf_off, mrg_copy_bytes);
>> +                if (err)
>> +                    goto out;
>> +
>> +                tmp_bytes -= mrg_copy_bytes;
>> +                pkt->off += mrg_copy_bytes;
>> +                last_buf_total += buf[i].len;
>> +                if (!tmp_bytes)
>> +                    break;
>> +            }
> 
> 
> After switch to use iov, you can user iov_iter helper to avoid the above open-coding I believe.
> 
> And you can also drop the if (mergeable) condition.
> 
> Thanks
> 

Thanks, I will try to use iov instead.

> 
>> +
>> +            if (tmp_bytes) {
>> +                printk(KERN_WARNING "WARNING! bytes = %llu, "
>> +                        "bytes = %llu\n",
>> +                        (unsigned long long)bytes,
>> +                        (unsigned long long)tmp_bytes);
>> +            }
>> +
>> +            total += (bytes - tmp_bytes);
>> +        } else {
>> +            err = memcpy_to_msg(msg, pkt->buf + pkt->off, bytes);
>> +            if (err)
>> +                goto out;
>> +
>> +            total += bytes;
>> +            pkt->off += bytes;
>> +        }
>>
>>           spin_lock_bh(&vvs->rx_lock);
>> -
>> -        total += bytes;
>> -        pkt->off += bytes;
>>           if (pkt->off == pkt->len) {
>>               virtio_transport_dec_rx_pkt(vvs, pkt);
>>               list_del(&pkt->list);
>> @@ -1050,8 +1085,16 @@ void virtio_transport_recv_pkt(struct virtio_vsock_pkt *pkt)
>>
>>   void virtio_transport_free_pkt(struct virtio_vsock_pkt *pkt)
>>   {
>> -    kfree(pkt->buf);
>> -    kfree(pkt);
>> +    int i;
>> +
>> +    if (pkt->mergeable) {
>> +        for (i = 1; i < le16_to_cpu(pkt->mrg_rxbuf_hdr.num_buffers); i++)
>> +            free_page((unsigned long)pkt->mrg_rxbuf[i].buf);
>> +        free_page((unsigned long)(void *)pkt);
>> +    } else {
>> +        kfree(pkt->buf);
>> +        kfree(pkt);
>> +    }
>>   }
>>   EXPORT_SYMBOL_GPL(virtio_transport_free_pkt);
>>
> 
> .
>