linux-kernel - Re: [PATCH] hv_sock: Return the readable bytes in hvs_stream_has

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Message-ID: <346e4b8a-2e62-420b-9816-6a35b8b63da1@redhat.com>
Date: Tue, 1 Jul 2025 15:04:37 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Dexuan Cui <decui@...rosoft.com>, niuxuewei97@...il.com,
 kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
 sgarzare@...hat.com, davem@...emloft.net, edumazet@...gle.com,
 kuba@...nel.org, horms@...nel.org, linux-hyperv@...r.kernel.org,
 virtualization@...ts.linux.dev, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hv_sock: Return the readable bytes in
 hvs_stream_has_data()

On 6/27/25 10:44 AM, Dexuan Cui 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
> 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>
> ---
> 
> Hi maintainers, please don't take the patch for now.
> 
> Hi Xuewei Niu, please help to re-post this patch with the next version
> of your patchset "vsock: Introduce SIOCINQ ioctl support". See
> https://lore.kernel.org/virtualization/BL1PR21MB3115F69C544B0FAA145FA4EABF7BA@BL1PR21MB3115.namprd21.prod.outlook.com/#t
> https://lore.kernel.org/virtualization/20250626050219.1847316-1-niuxuewei.nxw@antgroup.com/
> Feel free to add your Signed-off-by, if you need.
> 
>  net/vmw_vsock/hyperv_transport.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c
> index 31342ab502b4..64f1290a9ae7 100644
> --- a/net/vmw_vsock/hyperv_transport.c
> +++ b/net/vmw_vsock/hyperv_transport.c
> @@ -694,15 +694,25 @@ 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 = !hvs->recv_desc;
>  	s64 ret;

Minor nit: when reposting please respect the reverse christmas tree
order above moving 'need_refill' initialization after the following 'if'
statement.

/P