linux-kernel - Re: [PATCH net-next v1 02/12] vsock: read from socket's error queue

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Message-ID: <j7e5az5xrrqvvs64dhwaboi5d4ls5aueu3gyeyyasdqmzbsozu@fni6x6mliw3t>
Date:   Wed, 27 Sep 2023 09:34:33 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Arseniy Krasnov <avkrasnov@...utedevices.com>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Bobby Eshleman <bobby.eshleman@...edance.com>,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...rdevices.ru, oxffffaa@...il.com
Subject: Re: [PATCH net-next v1 02/12] vsock: read from socket's error queue

On Tue, Sep 26, 2023 at 10:36:58PM +0300, Arseniy Krasnov wrote:
>
>
>On 26.09.2023 15:55, Stefano Garzarella wrote:
>> On Fri, Sep 22, 2023 at 08:24:18AM +0300, Arseniy Krasnov wrote:
>>> This adds handling of MSG_ERRQUEUE input flag in receive call. This flag
>>> is used to read socket's error queue instead of data queue. Possible
>>> scenario of error queue usage is receiving completions for transmission
>>> with MSG_ZEROCOPY flag. This patch also adds new defines: 'SOL_VSOCK'
>>> and 'VSOCK_RECVERR'.
>>>
>>> Signed-off-by: Arseniy Krasnov <avkrasnov@...utedevices.com>
>>> ---
>>> Changelog:
>>> v5(big patchset) -> v1:
>>>  * R-b tag removed, due to added defines to 'include/uapi/linux/vsock.h'.
>>>    Both 'SOL_VSOCK' and 'VSOCK_RECVERR' are needed by userspace, so
>>>    they were placed to 'include/uapi/linux/vsock.h'. At the same time,
>>>    the same define for 'SOL_VSOCK' was placed to 'include/linux/socket.h'.
>>>    This is needed because this file contains SOL_XXX defines for different
>>>    types of socket, so it prevents situation when another new SOL_XXX
>>>    will use constant 287.
>>>
>>> include/linux/socket.h     | 1 +
>>> include/uapi/linux/vsock.h | 9 +++++++++
>>> net/vmw_vsock/af_vsock.c   | 6 ++++++
>>> 3 files changed, 16 insertions(+)
>>> create mode 100644 include/uapi/linux/vsock.h
>>>
>>> diff --git a/include/linux/socket.h b/include/linux/socket.h
>>> index 39b74d83c7c4..cfcb7e2c3813 100644
>>> --- a/include/linux/socket.h
>>> +++ b/include/linux/socket.h
>>> @@ -383,6 +383,7 @@ struct ucred {
>>> #define SOL_MPTCP    284
>>> #define SOL_MCTP    285
>>> #define SOL_SMC        286
>>> +#define SOL_VSOCK    287
>>>
>>> /* IPX options */
>>> #define IPX_TYPE    1
>>> diff --git a/include/uapi/linux/vsock.h b/include/uapi/linux/vsock.h
>>> new file mode 100644
>>> index 000000000000..b25c1347a3b8
>>> --- /dev/null
>>> +++ b/include/uapi/linux/vsock.h
>>
>> We already have include/uapi/linux/vm_sockets.h
>>
>> Should we include these changes there instead of creating a new header?
>>
>>> @@ -0,0 +1,9 @@
>>> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
>>> +#ifndef _UAPI_LINUX_VSOCK_H
>>> +#define _UAPI_LINUX_VSOCK_H
>>> +
>>> +#define SOL_VSOCK    287
>>
>> Why we need to re-define this also here?
>
>Reason of this re-define is that SOL_VSOCK must be exported to userspace, so
>i place it to include/uapi/XXX. At the same time include/linux/socket.h contains
>constants for SOL_XXX and they goes sequentially in this file (e.g. one by one,
>each new value is +1 to the previous). So if I add SOL_VSOCK to include/uapi/XXX
>only, it is possible that someone will add new SOL_VERY_NEW_SOCKET == 287 to
>include/linux/socket.h in future. I think it is not good that two SOL_XXX will
>have same value.
>
>For example SOL_RDS and SOL_TIPS uses the same approach - there are two same defines:
>one in include/uapi/ and another is in include/linux/socket.h

Okay, I was confused, I though socket.h was the uapi one.
If others do the same, it's fine.

But why adding a new vsock.h instead of reusing vm_sockets.h?

>
>>
>> In that case, should we protect with some guards to avoid double
>> defines?
>
>May be:
>
>in include/linux/socket.h
>
>#ifndef SOL_VSOCK
>#define SOL_VSOCK 287
>#endif
>
>But not sure...

Nope, let's follow others definition.

Sorry for the confusion ;-)

>
>>
>>> +
>>> +#define VSOCK_RECVERR    1
>>> +
>>> +#endif /* _UAPI_LINUX_VSOCK_H */
>>> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
>>> index d841f4de33b0..4fd11bf34bc7 100644
>>> --- a/net/vmw_vsock/af_vsock.c
>>> +++ b/net/vmw_vsock/af_vsock.c
>>> @@ -110,6 +110,8 @@
>>> #include <linux/workqueue.h>
>>> #include <net/sock.h>
>>> #include <net/af_vsock.h>
>>> +#include <linux/errqueue.h>
>>> +#include <uapi/linux/vsock.h>
>>>
>>> static int __vsock_bind(struct sock *sk, struct sockaddr_vm *addr);
>>> static void vsock_sk_destruct(struct sock *sk);
>>> @@ -2137,6 +2139,10 @@ vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
>>>     int err;
>>>
>>>     sk = sock->sk;
>>> +
>>> +    if (unlikely(flags & MSG_ERRQUEUE))
>>> +        return sock_recv_errqueue(sk, msg, len, SOL_VSOCK, 
>>> VSOCK_RECVERR);
>>> +
>>>     vsk = vsock_sk(sk);
>>>     err = 0;
>>>
>>> -- 
>>> 2.25.1
>>>
>>
>