linux-kernel - Re: [PATCH net-next v5 1/4] hv_sock: Return the readable bytes in hvs_stream_has

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Message-ID: <aaac1fda-7365-4643-b8df-df6412a42891@antgroup.com>
Date: Tue, 8 Jul 2025 13:17:36 +0800
From: Xuewei Niu <niuxuewei.nxw@...group.com>
To: Stefano Garzarella <sgarzare@...hat.com>,
 Xuewei Niu <niuxuewei97@...il.com>
Cc: "K. Y. Srinivasan" <kys@...rosoft.com>,
 Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>,
 Dexuan Cui <decui@...rosoft.com>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
 linux-hyperv@...r.kernel.org, virtualization@...ts.linux.dev,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org, fupan.lfp@...group.com
Subject: Re: [PATCH net-next v5 1/4] hv_sock: Return the readable bytes in
 hvs_stream_has_data()



On 2025/7/7 21:42, Stefano Garzarella wrote:
> On Sun, Jul 06, 2025 at 12:36:29PM +0800, Xuewei Niu wrote:
>> When hv_sock was originally added, __vsock_stream_recvmsg() and
>> vsock_stream_has_data() actually only needed to know whether there
>> is any readable data or not, so hvs_stream_has_data() was written to
>> return 1 or 0 for simplicity.
>>
>> However, now hvs_stream_has_data() should return the readable bytes
>> because vsock_data_ready() -> vsock_stream_has_data() needs to know the
>> actual bytes rather than a boolean value of 1 or 0.
>>
>> The SIOCINQ ioctl support also needs hvs_stream_has_data() to return
>> the readable bytes.
>>
>> Let hvs_stream_has_data() return the readable bytes of the payload in
>> the next host-to-guest VMBus hv_sock packet.
>>
>> Note: there may be multpile incoming hv_sock packets pending in the
> 
> s/multpile/multiple

Will do.

Thanks,
Xuewei

>> VMBus channel's ringbuffer, but so far there is not a VMBus API that
>> allows us to know all the readable bytes in total without reading and
>> caching the payload of the multiple packets, so let's just return the
>> readable bytes of the next single packet. In the future, we'll either
>> add a VMBus API that allows us to know the total readable bytes without
>> touching the data in the ringbuffer, or the hv_sock driver needs to
>> understand the VMBus packet format and parse the packets directly.
>>
>> Signed-off-by: Dexuan Cui <decui@...rosoft.com>
>> ---
>> net/vmw_vsock/hyperv_transport.c | 17 ++++++++++++++---
>> 1 file changed, 14 insertions(+), 3 deletions(-)
>>
>> diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c
>> index 31342ab502b4fc35feb812d2c94e0e35ded73771..432fcbbd14d4f44bd2550be8376e42ce65122758 100644
>> --- a/net/vmw_vsock/hyperv_transport.c
>> +++ b/net/vmw_vsock/hyperv_transport.c
>> @@ -694,15 +694,26 @@ static ssize_t hvs_stream_enqueue(struct vsock_sock *vsk, struct msghdr *msg,
>> static s64 hvs_stream_has_data(struct vsock_sock *vsk)
>> {
>>     struct hvsock *hvs = vsk->trans;
>> +    bool need_refill;
>>     s64 ret;
>>
>>     if (hvs->recv_data_len > 0)
>> -        return 1;
>> +        return hvs->recv_data_len;
>>
>>     switch (hvs_channel_readable_payload(hvs->chan)) {
>>     case 1:
>> -        ret = 1;
>> -        break;
>> +        need_refill = !hvs->recv_desc;
>> +        if (!need_refill)
>> +            return -EIO;
>> +
>> +        hvs->recv_desc = hv_pkt_iter_first(hvs->chan);
>> +        if (!hvs->recv_desc)
>> +            return -ENOBUFS;
>> +
>> +        ret = hvs_update_recv_data(hvs);
>> +        if (ret)
>> +            return ret;
>> +        return hvs->recv_data_len;
>>     case 0:
>>         vsk->peer_shutdown |= SEND_SHUTDOWN;
>>         ret = 0;
>>
>> -- 
>> 2.34.1
>>