netdev - Re: [PATCH net-next v3 1/4] vsock/virtio: Linger on unsent data

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Message-ID: <23bcd402-86f9-4c05-bb83-360c8e4438fc@rbox.co>
Date: Wed, 30 Apr 2025 12:28:48 +0200
From: Michal Luczaj <mhal@...x.co>
To: Stefano Garzarella <sgarzare@...hat.com>
Cc: "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>,
 "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez
 <eperezma@...hat.com>, Stefan Hajnoczi <stefanha@...hat.com>,
 virtualization@...ts.linux.dev, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH net-next v3 1/4] vsock/virtio: Linger on unsent data

On 4/30/25 11:26, Stefano Garzarella wrote:
> On Wed, Apr 30, 2025 at 11:10:27AM +0200, Michal Luczaj wrote:
>> Currently vsock's lingering effectively boils down to waiting (or timing
>> out) until packets are consumed or dropped by the peer; be it by receiving
>> the data, closing or shutting down the connection.
>>
>> To align with the semantics described in the SO_LINGER section of man
>> socket(7) and to mimic AF_INET's behaviour more closely, change the logic
>> of a lingering close(): instead of waiting for all data to be handled,
>> block until data is considered sent from the vsock's transport point of
>> view. That is until worker picks the packets for processing and decrements
>> virtio_vsock_sock::bytes_unsent down to 0.
>>
>> Note that (some interpretation of) lingering was always limited to
>> transports that called virtio_transport_wait_close() on transport release.
>> This does not change, i.e. under Hyper-V and VMCI no lingering would be
>> observed.
>>
>> The implementation does not adhere strictly to man page's interpretation of
>> SO_LINGER: shutdown() will not trigger the lingering. This follows AF_INET.
>>
>> Signed-off-by: Michal Luczaj <mhal@...x.co>
>> ---
>> net/vmw_vsock/virtio_transport_common.c | 8 ++++++--
>> 1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>> index 7f7de6d8809655fe522749fbbc9025df71f071bd..49c6617b467195ba385cc3db86caa4321b422d7a 100644
>> --- a/net/vmw_vsock/virtio_transport_common.c
>> +++ b/net/vmw_vsock/virtio_transport_common.c
>> @@ -1196,12 +1196,16 @@ static void virtio_transport_wait_close(struct sock *sk, long timeout)
>> {
>> 	if (timeout) {
>> 		DEFINE_WAIT_FUNC(wait, woken_wake_function);
>> +		ssize_t (*unsent)(struct vsock_sock *vsk);
>> +		struct vsock_sock *vsk = vsock_sk(sk);
>> +
>> +		unsent = vsk->transport->unsent_bytes;
> 
> Just use `virtio_transport_unsent_bytes`, we don't need to be generic on 
> transport here.

All right.

Thanks