linux-kernel - Re: [PATCH net-next v3 02/12] vsock: read from socket's error queue

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Message-ID: <v3w46qfwgi66omysu64ma3lac437wy3j47a6vdbtr4umxfcrvv@4y2ypaub2k22>
Date:   Mon, 9 Oct 2023 17:16:49 +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 v3 02/12] vsock: read from socket's error queue

On Sat, Oct 07, 2023 at 08:21:29PM +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:
> v1 -> v2:
>  * Place new defines for userspace to the existing file 'vm_sockets.h'
>    instead of creating new one.
> v2 -> v3:
>  * Add comments to describe 'SOL_VSOCK' and 'VSOCK_RECVERR' in the file
>    'vm_sockets.h'.
>  * Reorder includes in 'af_vsock.c' in alphabetical order.
>
> include/linux/socket.h          |  1 +
> include/uapi/linux/vm_sockets.h | 12 ++++++++++++
> net/vmw_vsock/af_vsock.c        |  6 ++++++
> 3 files changed, 19 insertions(+)
>
>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/vm_sockets.h b/include/uapi/linux/vm_sockets.h
>index c60ca33eac59..d9d703b2d45a 100644
>--- a/include/uapi/linux/vm_sockets.h
>+++ b/include/uapi/linux/vm_sockets.h
>@@ -191,4 +191,16 @@ struct sockaddr_vm {
>
> #define IOCTL_VM_SOCKETS_GET_LOCAL_CID		_IO(7, 0xb9)
>
>+/* For reading completion in case of MSG_ZEROCOPY flag transmission.
>+ * This is value of 'cmsg_level' field of the 'struct cmsghdr'.
>+ */
>+
>+#define SOL_VSOCK	287
>+
>+/* For reading completion in case of MSG_ZEROCOPY flag transmission.
>+ * This is value of 'cmsg_type' field of the 'struct cmsghdr'.
>+ */
>+
>+#define VSOCK_RECVERR	1

I would suggest a bit more context here, something like this:

diff --git a/include/uapi/linux/vm_sockets.h b/include/uapi/linux/vm_sockets.h
index d9d703b2d45a..ed07181d4eff 100644
--- a/include/uapi/linux/vm_sockets.h
+++ b/include/uapi/linux/vm_sockets.h
@@ -191,14 +191,19 @@ struct sockaddr_vm {

  #define IOCTL_VM_SOCKETS_GET_LOCAL_CID         _IO(7, 0xb9)

-/* For reading completion in case of MSG_ZEROCOPY flag transmission.
- * This is value of 'cmsg_level' field of the 'struct cmsghdr'.
+/* MSG_ZEROCOPY notifications are encoded in the standard error format,
+ * sock_extended_err. See Documentation/networking/msg_zerocopy.rst in
+ * kernel source tree for more details.
+ */
+
+/* 'cmsg_level' field value of 'struct cmsghdr' for notification parsing
+ * when MSG_ZEROCOPY flag is used on transmissions.
   */

  #define SOL_VSOCK      287

-/* For reading completion in case of MSG_ZEROCOPY flag transmission.
- * This is value of 'cmsg_type' field of the 'struct cmsghdr'.
+/* 'cmsg_type' field value of 'struct cmsghdr' for notification parsing
+ * when MSG_ZEROCOPY flag is used on transmissions.
   */

  #define VSOCK_RECVERR  1

The rest LGTM.

Stefano

>+
> #endif /* _UAPI_VM_SOCKETS_H */
>diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
>index d841f4de33b0..38486efd3d05 100644
>--- a/net/vmw_vsock/af_vsock.c
>+++ b/net/vmw_vsock/af_vsock.c
>@@ -89,6 +89,7 @@
> #include <linux/types.h>
> #include <linux/bitops.h>
> #include <linux/cred.h>
>+#include <linux/errqueue.h>
> #include <linux/init.h>
> #include <linux/io.h>
> #include <linux/kernel.h>
>@@ -110,6 +111,7 @@
> #include <linux/workqueue.h>
> #include <net/sock.h>
> #include <net/af_vsock.h>
>+#include <uapi/linux/vm_sockets.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
>