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

[Stefano Garzarella]

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@xxxxxxxxxxxxxxxxx>
> ---
> 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