linux-kernel - Re: [PATCH net 1/2] vsock: Make accept()ed sockets use custom setsockopt()

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Message-ID: <aUqI_qW3SZ-WBXk3@sgarzare-redhat>
Date: Tue, 23 Dec 2025 14:15:56 +0100
From: Stefano Garzarella <sgarzare@...hat.com>
To: Michal Luczaj <mhal@...x.co>
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>, 
	Arseniy Krasnov <avkrasnov@...utedevices.com>, virtualization@...ts.linux.dev, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 1/2] vsock: Make accept()ed sockets use custom
 setsockopt()

On Tue, Dec 23, 2025 at 12:09:51PM +0100, Michal Luczaj wrote:
>On 12/23/25 11:26, Stefano Garzarella wrote:
>> On Tue, Dec 23, 2025 at 10:15:28AM +0100, Michal Luczaj wrote:
>...
>>> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
>>> index adcba1b7bf74..c093db8fec2d 100644
>>> --- a/net/vmw_vsock/af_vsock.c
>>> +++ b/net/vmw_vsock/af_vsock.c
>>> @@ -1787,6 +1787,7 @@ static int vsock_accept(struct socket *sock, struct socket *newsock,
>>> 		} else {
>>> 			newsock->state = SS_CONNECTED;
>>> 			sock_graft(connected, newsock);
>>> +			set_bit(SOCK_CUSTOM_SOCKOPT, &newsock->flags);
>>
>> I was a bit confused about next lines calling set_bit on
>> `connected->sk_socket->flags`, but after `sock_graft(connected,
>> newsock)` they are equivalent.
>>
>> So, maybe I would move the new line before the sock_graft() call or use
>> `connected->sk_socket->flags` if you want to keep it after it.
>...
>>> 			if (vsock_msgzerocopy_allow(vconnected->transport))
>>> 				set_bit(SOCK_SUPPORT_ZC,
>>> 					&connected->sk_socket->flags);
>
>Hmm, isn't using both `connected->sk_socket->flags` and `newsock->flags` a
>bit confusing?

Yep, for that reason I suggested to use `connected->sk_socket->flags`.

>`connected->sk_socket->flags` feels unnecessary long to me.
>So how about a not-so-minimal-patch to have
>
>	newsock->state = SS_CONNECTED;
>	set_bit(SOCK_CUSTOM_SOCKOPT, &newsock->flags);
>	if (vsock_msgzerocopy_allow(vconnected->transport))
>		set_bit(SOCK_SUPPORT_ZC, &newsock->flags);
>	sock_graft(connected, newsock);

No, please, this is a fix, so let's touch less as possible.

As I mentioned before, we have 2 options IMO:
1. use `set_bit(SOCK_CUSTOM_SOCKOPT, &newsock->flags);` but move it
    before `sock_graft()`
2. use `connected->sk_socket->flags` and set it after `sock_graft()` if
    we want to be a bit more consistent

I'd go with option 2, because I like to be consistent and it's less
confusing IMHO, but I'm fine also with option 1.

Thanks,
Stefano