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Message-ID: <6615b0a417f7a_24a51429479@willemb.c.googlers.com.notmuch>
Date: Tue, 09 Apr 2024 17:18:28 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: zijianzhang@...edance.com,
netdev@...r.kernel.org
Cc: edumazet@...gle.com,
willemdebruijn.kernel@...il.com,
davem@...emloft.net,
kuba@...nel.org,
cong.wang@...edance.com,
xiaochun.lu@...edance.com,
Zijian Zhang <zijianzhang@...edance.com>
Subject: Re: [PATCH net-next 1/3] sock: add MSG_ZEROCOPY_UARG
zijianzhang@ wrote:
> From: Zijian Zhang <zijianzhang@...edance.com>
>
> The MSG_ZEROCOPY flag enables copy avoidance for socket send calls.
> However, zerocopy is not a free lunch. Apart from the management of user
> pages, the combination of poll + recvmsg to receive notifications incurs
> unignorable overhead in the applications. The overhead of such sometimes
> might be more than the CPU savings from zerocopy. We try to solve this
> problem with a new option for TCP and UDP, MSG_ZEROCOPY_UARG.
> This new mechanism aims to reduce the overhead associated with receiving
> notifications by embedding them directly into user arguments passed with
> each sendmsg control message. By doing so, we can significantly reduce
> the complexity and overhead for managing notifications. In an ideal
> pattern, the user will keep calling sendmsg with MSG_ZEROCOPY_UARG
> flag, and the notification will be delivered as soon as possible.
>
> Signed-off-by: Zijian Zhang <zijianzhang@...edance.com>
> Signed-off-by: Xiaochun Lu <xiaochun.lu@...edance.com>
The idea to avoid POLLERR and errqueue receive cost by piggy-backing
onto the send() call is appealing.
I also implemented this when initially adding MSG_ZEROCOPY. At the
time my implementation did not warrant the modest performance
improvement I measured. But this may be different.
The main reason my code was complex is that this requires changes
to net/socket.c: controldata is intended to be user->kernel on
send and kernel->user on recv, such as data. This feature breaks
that. You'll have to copy msg_controldata in ____sys_sendmsg.
I don't think it requires this much new infrastructure: a separate
queue in structs tcp_sock and udp_sock, a differente uarg callback.
I would suggest an optimistic algorithm, whereby the send call
steaks a notification skb from the error queue if present. This
could be a new mode set with a value 2 in SO_ZEROCOPY.
> ---
> include/linux/skbuff.h | 7 +-
> include/linux/socket.h | 1 +
> include/linux/tcp.h | 3 +
> include/linux/udp.h | 3 +
> include/net/sock.h | 17 +++
> include/net/udp.h | 1 +
> include/uapi/asm-generic/socket.h | 2 +
> include/uapi/linux/socket.h | 17 +++
> net/core/skbuff.c | 137 ++++++++++++++++++++++--
> net/core/sock.c | 50 +++++++++
> net/ipv4/ip_output.c | 6 +-
> net/ipv4/tcp.c | 7 +-
> net/ipv4/udp.c | 9 ++
> net/ipv6/ip6_output.c | 5 +-
> net/ipv6/udp.c | 9 ++
> net/vmw_vsock/virtio_transport_common.c | 2 +-
> 16 files changed, 258 insertions(+), 18 deletions(-)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 03ea36a82cdd..19b94ba01007 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -1663,12 +1663,14 @@ static inline void skb_set_end_offset(struct sk_buff *skb, unsigned int offset)
> #endif
>
> struct ubuf_info *msg_zerocopy_realloc(struct sock *sk, size_t size,
> - struct ubuf_info *uarg);
> + struct ubuf_info *uarg, bool user_args_notification);
>
> void msg_zerocopy_put_abort(struct ubuf_info *uarg, bool have_uref);
>
> void msg_zerocopy_callback(struct sk_buff *skb, struct ubuf_info *uarg,
> bool success);
> +void msg_zerocopy_uarg_callback(struct sk_buff *skb, struct ubuf_info *uarg,
> + bool success);
>
> int __zerocopy_sg_from_iter(struct msghdr *msg, struct sock *sk,
> struct sk_buff *skb, struct iov_iter *from,
> @@ -1763,7 +1765,8 @@ static inline void net_zcopy_put(struct ubuf_info *uarg)
> static inline void net_zcopy_put_abort(struct ubuf_info *uarg, bool have_uref)
> {
> if (uarg) {
> - if (uarg->callback == msg_zerocopy_callback)
> + if (uarg->callback == msg_zerocopy_callback ||
> + uarg->callback == msg_zerocopy_uarg_callback)
> msg_zerocopy_put_abort(uarg, have_uref);
> else if (have_uref)
> net_zcopy_put(uarg);
> diff --git a/include/linux/socket.h b/include/linux/socket.h
> index 139c330ccf2c..de01392344e1 100644
> --- a/include/linux/socket.h
> +++ b/include/linux/socket.h
> @@ -326,6 +326,7 @@ struct ucred {
> * plain text and require encryption
> */
>
> +#define MSG_ZEROCOPY_UARG 0x2000000 /* MSG_ZEROCOPY with UARG notifications */
> #define MSG_ZEROCOPY 0x4000000 /* Use user data in kernel path */
> #define MSG_SPLICE_PAGES 0x8000000 /* Splice the pages from the iterator in sendmsg() */
> #define MSG_FASTOPEN 0x20000000 /* Send data in TCP SYN */
> diff --git a/include/linux/tcp.h b/include/linux/tcp.h
> index 55399ee2a57e..e973f4990646 100644
> --- a/include/linux/tcp.h
> +++ b/include/linux/tcp.h
> @@ -501,6 +501,9 @@ struct tcp_sock {
> */
> struct request_sock __rcu *fastopen_rsk;
> struct saved_syn *saved_syn;
> +
> +/* TCP MSG_ZEROCOPY_UARG related information */
> + struct tx_msg_zcopy_queue tx_zcopy_queue;
> };
>
> enum tsq_enum {
> diff --git a/include/linux/udp.h b/include/linux/udp.h
> index 3748e82b627b..502b393eac67 100644
> --- a/include/linux/udp.h
> +++ b/include/linux/udp.h
> @@ -95,6 +95,9 @@ struct udp_sock {
>
> /* Cache friendly copy of sk->sk_peek_off >= 0 */
> bool peeking_with_offset;
> +
> + /* This field is used by sendmsg zcopy user arg mode notification */
> + struct tx_msg_zcopy_queue tx_zcopy_queue;
> };
>
> #define udp_test_bit(nr, sk) \
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 2253eefe2848..f7c045e98213 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -544,6 +544,23 @@ struct sock {
> netns_tracker ns_tracker;
> };
>
> +struct tx_msg_zcopy_node {
> + struct list_head node;
> + struct tx_msg_zcopy_info info;
> + struct sk_buff *skb;
> +};
> +
> +struct tx_msg_zcopy_queue {
> + struct list_head head;
> + spinlock_t lock; /* protects head queue */
> +};
> +
> +static inline void tx_message_zcopy_queue_init(struct tx_msg_zcopy_queue *q)
> +{
> + spin_lock_init(&q->lock);
> + INIT_LIST_HEAD(&q->head);
> +}
> +
> enum sk_pacing {
> SK_PACING_NONE = 0,
> SK_PACING_NEEDED = 1,
> diff --git a/include/net/udp.h b/include/net/udp.h
> index 488a6d2babcc..9e4d7b128de4 100644
> --- a/include/net/udp.h
> +++ b/include/net/udp.h
> @@ -182,6 +182,7 @@ static inline void udp_lib_init_sock(struct sock *sk)
> skb_queue_head_init(&up->reader_queue);
> up->forward_threshold = sk->sk_rcvbuf >> 2;
> set_bit(SOCK_CUSTOM_SOCKOPT, &sk->sk_socket->flags);
> + tx_message_zcopy_queue_init(&up->tx_zcopy_queue);
> }
>
> /* hash routines shared between UDPv4/6 and UDP-Litev4/6 */
> diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
> index 8ce8a39a1e5f..86aa4b5cb7f1 100644
> --- a/include/uapi/asm-generic/socket.h
> +++ b/include/uapi/asm-generic/socket.h
> @@ -135,6 +135,8 @@
> #define SO_PASSPIDFD 76
> #define SO_PEERPIDFD 77
>
> +#define SO_ZEROCOPY_NOTIFICATION 78
> +
> #if !defined(__KERNEL__)
>
> #if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))
> diff --git a/include/uapi/linux/socket.h b/include/uapi/linux/socket.h
> index d3fcd3b5ec53..469ed8f4e6c8 100644
> --- a/include/uapi/linux/socket.h
> +++ b/include/uapi/linux/socket.h
> @@ -35,4 +35,21 @@ struct __kernel_sockaddr_storage {
> #define SOCK_TXREHASH_DISABLED 0
> #define SOCK_TXREHASH_ENABLED 1
>
> +/*
> + * Given the fact that MSG_ZEROCOPY_UARG tries to copy notifications
> + * back to user as soon as possible, 8 should be sufficient.
> + */
> +#define SOCK_USR_ZC_INFO_MAX 8
> +
> +struct tx_msg_zcopy_info {
> + __u32 lo;
> + __u32 hi;
> + __u8 zerocopy;
> +};
> +
> +struct tx_usr_zcopy_info {
> + int length;
> + struct tx_msg_zcopy_info info[SOCK_USR_ZC_INFO_MAX];
> +};
> +
> #endif /* _UAPI_LINUX_SOCKET_H */
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 2a5ce6667bbb..d939b2c14d55 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -1661,6 +1661,16 @@ void mm_unaccount_pinned_pages(struct mmpin *mmp)
> }
> EXPORT_SYMBOL_GPL(mm_unaccount_pinned_pages);
>
> +static void init_ubuf_info_msgzc(struct ubuf_info_msgzc *uarg, struct sock *sk, size_t size)
> +{
> + uarg->id = ((u32)atomic_inc_return(&sk->sk_zckey)) - 1;
> + uarg->len = 1;
> + uarg->bytelen = size;
> + uarg->zerocopy = 1;
> + uarg->ubuf.flags = SKBFL_ZEROCOPY_FRAG | SKBFL_DONT_ORPHAN;
> + refcount_set(&uarg->ubuf.refcnt, 1);
> +}
> +
> static struct ubuf_info *msg_zerocopy_alloc(struct sock *sk, size_t size)
> {
> struct ubuf_info_msgzc *uarg;
> @@ -1682,12 +1692,38 @@ static struct ubuf_info *msg_zerocopy_alloc(struct sock *sk, size_t size)
> }
>
> uarg->ubuf.callback = msg_zerocopy_callback;
> - uarg->id = ((u32)atomic_inc_return(&sk->sk_zckey)) - 1;
> - uarg->len = 1;
> - uarg->bytelen = size;
> - uarg->zerocopy = 1;
> - uarg->ubuf.flags = SKBFL_ZEROCOPY_FRAG | SKBFL_DONT_ORPHAN;
> - refcount_set(&uarg->ubuf.refcnt, 1);
> + init_ubuf_info_msgzc(uarg, sk, size);
> + sock_hold(sk);
> +
> + return &uarg->ubuf;
> +}
> +
> +static struct ubuf_info *msg_zerocopy_uarg_alloc(struct sock *sk, size_t size)
> +{
> + struct sk_buff *skb;
> + struct ubuf_info_msgzc *uarg;
> + struct tx_msg_zcopy_node *zcopy_node_p;
> +
> + WARN_ON_ONCE(!in_task());
> +
> + skb = sock_omalloc(sk, sizeof(*zcopy_node_p), GFP_KERNEL);
> + if (!skb)
> + return NULL;
> +
> + BUILD_BUG_ON(sizeof(*uarg) > sizeof(skb->cb));
> + uarg = (void *)skb->cb;
> + uarg->mmp.user = NULL;
> + zcopy_node_p = (struct tx_msg_zcopy_node *)skb_put(skb, sizeof(*zcopy_node_p));
> +
> + if (mm_account_pinned_pages(&uarg->mmp, size)) {
> + kfree_skb(skb);
> + return NULL;
> + }
> +
> + INIT_LIST_HEAD(&zcopy_node_p->node);
> + zcopy_node_p->skb = skb;
> + uarg->ubuf.callback = msg_zerocopy_uarg_callback;
> + init_ubuf_info_msgzc(uarg, sk, size);
> sock_hold(sk);
>
> return &uarg->ubuf;
> @@ -1699,7 +1735,7 @@ static inline struct sk_buff *skb_from_uarg(struct ubuf_info_msgzc *uarg)
> }
>
> struct ubuf_info *msg_zerocopy_realloc(struct sock *sk, size_t size,
> - struct ubuf_info *uarg)
> + struct ubuf_info *uarg, bool usr_arg_notification)
> {
> if (uarg) {
> struct ubuf_info_msgzc *uarg_zc;
> @@ -1707,7 +1743,8 @@ struct ubuf_info *msg_zerocopy_realloc(struct sock *sk, size_t size,
> u32 bytelen, next;
>
> /* there might be non MSG_ZEROCOPY users */
> - if (uarg->callback != msg_zerocopy_callback)
> + if (uarg->callback != msg_zerocopy_callback &&
> + uarg->callback != msg_zerocopy_uarg_callback)
> return NULL;
>
> /* realloc only when socket is locked (TCP, UDP cork),
> @@ -1744,6 +1781,8 @@ struct ubuf_info *msg_zerocopy_realloc(struct sock *sk, size_t size,
> }
>
> new_alloc:
> + if (usr_arg_notification)
> + return msg_zerocopy_uarg_alloc(sk, size);
> return msg_zerocopy_alloc(sk, size);
> }
> EXPORT_SYMBOL_GPL(msg_zerocopy_realloc);
> @@ -1830,6 +1869,86 @@ void msg_zerocopy_callback(struct sk_buff *skb, struct ubuf_info *uarg,
> }
> EXPORT_SYMBOL_GPL(msg_zerocopy_callback);
>
> +static bool skb_zerocopy_uarg_notify_extend(struct tx_msg_zcopy_node *node, u32 lo, u16 len)
> +{
> + u32 old_lo, old_hi;
> + u64 sum_len;
> +
> + old_lo = node->info.lo;
> + old_hi = node->info.hi;
> + sum_len = old_hi - old_lo + 1ULL + len;
> +
> + if (sum_len >= (1ULL << 32))
> + return false;
> +
> + if (lo != old_hi + 1)
> + return false;
> +
> + node->info.hi += len;
> + return true;
> +}
> +
> +static void __msg_zerocopy_uarg_callback(struct ubuf_info_msgzc *uarg)
> +{
> + struct sk_buff *skb = skb_from_uarg(uarg);
> + struct sock *sk = skb->sk;
> + struct tx_msg_zcopy_node *zcopy_node_p, *tail;
> + struct tx_msg_zcopy_queue *zcopy_queue;
> + unsigned long flags;
> + u32 lo, hi;
> + u16 len;
> +
> + mm_unaccount_pinned_pages(&uarg->mmp);
> +
> + /* if !len, there was only 1 call, and it was aborted
> + * so do not queue a completion notification
> + */
> + if (!uarg->len || sock_flag(sk, SOCK_DEAD))
> + goto release;
> +
> + /* only support TCP and UCP currently */
> + if (sk_is_tcp(sk)) {
> + zcopy_queue = &tcp_sk(sk)->tx_zcopy_queue;
> + } else if (sk_is_udp(sk)) {
> + zcopy_queue = &udp_sk(sk)->tx_zcopy_queue;
> + } else {
> + pr_warn("MSG_ZEROCOPY_UARG only support TCP && UDP sockets");
> + goto release;
> + }
> +
> + len = uarg->len;
> + lo = uarg->id;
> + hi = uarg->id + len - 1;
> +
> + zcopy_node_p = (struct tx_msg_zcopy_node *)skb->data;
> + zcopy_node_p->info.lo = lo;
> + zcopy_node_p->info.hi = hi;
> + zcopy_node_p->info.zerocopy = uarg->zerocopy;
> +
> + spin_lock_irqsave(&zcopy_queue->lock, flags);
> + tail = list_last_entry(&zcopy_queue->head, struct tx_msg_zcopy_node, node);
> + if (!tail || !skb_zerocopy_uarg_notify_extend(tail, lo, len)) {
> + list_add_tail(&zcopy_node_p->node, &zcopy_queue->head);
> + skb = NULL;
> + }
> + spin_unlock_irqrestore(&zcopy_queue->lock, flags);
> +release:
> + consume_skb(skb);
> + sock_put(sk);
> +}
> +
> +void msg_zerocopy_uarg_callback(struct sk_buff *skb, struct ubuf_info *uarg,
> + bool success)
> +{
> + struct ubuf_info_msgzc *uarg_zc = uarg_to_msgzc(uarg);
> +
> + uarg_zc->zerocopy = uarg_zc->zerocopy & success;
> +
> + if (refcount_dec_and_test(&uarg->refcnt))
> + __msg_zerocopy_uarg_callback(uarg_zc);
> +}
> +EXPORT_SYMBOL_GPL(msg_zerocopy_uarg_callback);
> +
> void msg_zerocopy_put_abort(struct ubuf_info *uarg, bool have_uref)
> {
> struct sock *sk = skb_from_uarg(uarg_to_msgzc(uarg))->sk;
> @@ -1838,7 +1957,7 @@ void msg_zerocopy_put_abort(struct ubuf_info *uarg, bool have_uref)
> uarg_to_msgzc(uarg)->len--;
>
> if (have_uref)
> - msg_zerocopy_callback(NULL, uarg, true);
> + uarg->callback(NULL, uarg, true);
> }
> EXPORT_SYMBOL_GPL(msg_zerocopy_put_abort);
>
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 5ed411231fc7..a00ebd71f6ed 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -2843,6 +2843,56 @@ int __sock_cmsg_send(struct sock *sk, struct cmsghdr *cmsg,
> case SCM_RIGHTS:
> case SCM_CREDENTIALS:
> break;
> + case SO_ZEROCOPY_NOTIFICATION:
> + if (sock_flag(sk, SOCK_ZEROCOPY)) {
> + int i = 0;
> + struct tx_usr_zcopy_info sys_zcopy_info;
> + struct tx_msg_zcopy_node *zcopy_node_p, *tmp;
> + struct tx_msg_zcopy_queue *zcopy_queue;
> + struct tx_msg_zcopy_node *zcopy_node_ps[SOCK_USR_ZC_INFO_MAX];
> + unsigned long flags;
> +
> + if (cmsg->cmsg_len != CMSG_LEN(sizeof(void *)))
> + return -EINVAL;
> +
> + if (sk_is_tcp(sk))
> + zcopy_queue = &tcp_sk(sk)->tx_zcopy_queue;
> + else if (sk_is_udp(sk))
> + zcopy_queue = &udp_sk(sk)->tx_zcopy_queue;
> + else
> + return -EINVAL;
> +
> + spin_lock_irqsave(&zcopy_queue->lock, flags);
> + list_for_each_entry_safe(zcopy_node_p, tmp, &zcopy_queue->head, node) {
> + sys_zcopy_info.info[i].lo = zcopy_node_p->info.lo;
> + sys_zcopy_info.info[i].hi = zcopy_node_p->info.hi;
> + sys_zcopy_info.info[i].zerocopy = zcopy_node_p->info.zerocopy;
> + list_del(&zcopy_node_p->node);
> + zcopy_node_ps[i++] = zcopy_node_p;
> + if (i == SOCK_USR_ZC_INFO_MAX)
> + break;
> + }
> + spin_unlock_irqrestore(&zcopy_queue->lock, flags);
> +
> + if (i > 0) {
> + sys_zcopy_info.length = i;
> + if (unlikely(copy_to_user(*(void **)CMSG_DATA(cmsg),
> + &sys_zcopy_info,
> + sizeof(sys_zcopy_info))
> + )) {
> + spin_lock_irqsave(&zcopy_queue->lock, flags);
> + while (i > 0)
> + list_add(&zcopy_node_ps[--i]->node,
> + &zcopy_queue->head);
> + spin_unlock_irqrestore(&zcopy_queue->lock, flags);
> + return -EFAULT;
> + }
> +
> + while (i > 0)
> + consume_skb(zcopy_node_ps[--i]->skb);
> + }
> + }
> + break;
> default:
> return -EINVAL;
> }
> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
> index 1fe794967211..5adb737c4c01 100644
> --- a/net/ipv4/ip_output.c
> +++ b/net/ipv4/ip_output.c
> @@ -1005,7 +1005,7 @@ static int __ip_append_data(struct sock *sk,
> (!exthdrlen || (rt->dst.dev->features & NETIF_F_HW_ESP_TX_CSUM)))
> csummode = CHECKSUM_PARTIAL;
>
> - if ((flags & MSG_ZEROCOPY) && length) {
> + if (((flags & MSG_ZEROCOPY) || (flags & MSG_ZEROCOPY_UARG)) && length) {
> struct msghdr *msg = from;
>
> if (getfrag == ip_generic_getfrag && msg->msg_ubuf) {
> @@ -1022,7 +1022,9 @@ static int __ip_append_data(struct sock *sk,
> uarg = msg->msg_ubuf;
> }
> } else if (sock_flag(sk, SOCK_ZEROCOPY)) {
> - uarg = msg_zerocopy_realloc(sk, length, skb_zcopy(skb));
> + bool user_args = flags & MSG_ZEROCOPY_UARG;
> +
> + uarg = msg_zerocopy_realloc(sk, length, skb_zcopy(skb), user_args);
> if (!uarg)
> return -ENOBUFS;
> extra_uref = !skb_zcopy(skb); /* only ref on new uarg */
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index e767721b3a58..6254d0eef3af 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -462,6 +462,8 @@ void tcp_init_sock(struct sock *sk)
>
> set_bit(SOCK_SUPPORT_ZC, &sk->sk_socket->flags);
> sk_sockets_allocated_inc(sk);
> +
> + tx_message_zcopy_queue_init(&tp->tx_zcopy_queue);
> }
> EXPORT_SYMBOL(tcp_init_sock);
>
> @@ -1050,14 +1052,15 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
>
> flags = msg->msg_flags;
>
> - if ((flags & MSG_ZEROCOPY) && size) {
> + if (((flags & MSG_ZEROCOPY) || (flags & MSG_ZEROCOPY_UARG)) && size) {
> if (msg->msg_ubuf) {
> uarg = msg->msg_ubuf;
> if (sk->sk_route_caps & NETIF_F_SG)
> zc = MSG_ZEROCOPY;
> } else if (sock_flag(sk, SOCK_ZEROCOPY)) {
> + bool zc_uarg = flags & MSG_ZEROCOPY_UARG;
> skb = tcp_write_queue_tail(sk);
> - uarg = msg_zerocopy_realloc(sk, size, skb_zcopy(skb));
> + uarg = msg_zerocopy_realloc(sk, size, skb_zcopy(skb), zc_uarg);
> if (!uarg) {
> err = -ENOBUFS;
> goto out_err;
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index 11460d751e73..6c62aacd74d6 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -1126,6 +1126,15 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
> if (ipc.opt)
> free = 1;
> connected = 0;
> +
> + /* If len is zero and flag MSG_ZEROCOPY_UARG is set,
> + * it means this call just wants to get zcopy notifications
> + * instead of sending packets. It is useful when users
> + * finish sending and want to get trailing notifications.
> + */
> + if ((msg->msg_flags & MSG_ZEROCOPY_UARG) &&
> + sock_flag(sk, SOCK_ZEROCOPY) && len == 0)
> + return 0;
> }
> if (!ipc.opt) {
> struct ip_options_rcu *inet_opt;
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index b9dd3a66e423..891526ddd74c 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -1493,7 +1493,7 @@ static int __ip6_append_data(struct sock *sk,
> rt->dst.dev->features & (NETIF_F_IPV6_CSUM | NETIF_F_HW_CSUM))
> csummode = CHECKSUM_PARTIAL;
>
> - if ((flags & MSG_ZEROCOPY) && length) {
> + if (((flags & MSG_ZEROCOPY) || (flags & MSG_ZEROCOPY_UARG)) && length) {
> struct msghdr *msg = from;
>
> if (getfrag == ip_generic_getfrag && msg->msg_ubuf) {
> @@ -1510,7 +1510,8 @@ static int __ip6_append_data(struct sock *sk,
> uarg = msg->msg_ubuf;
> }
> } else if (sock_flag(sk, SOCK_ZEROCOPY)) {
> - uarg = msg_zerocopy_realloc(sk, length, skb_zcopy(skb));
> + uarg = msg_zerocopy_realloc(sk, length, skb_zcopy(skb),
> + flags & MSG_ZEROCOPY_UARG);
> if (!uarg)
> return -ENOBUFS;
> extra_uref = !skb_zcopy(skb); /* only ref on new uarg */
> diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
> index 2e4dc5e6137b..98f6905c5db9 100644
> --- a/net/ipv6/udp.c
> +++ b/net/ipv6/udp.c
> @@ -1490,6 +1490,15 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
> if (!(opt->opt_nflen|opt->opt_flen))
> opt = NULL;
> connected = false;
> +
> + /* If len is zero and flag MSG_ZEROCOPY_UARG is set,
> + * it means this call just wants to get zcopy notifications
> + * instead of sending packets. It is useful when users
> + * finish sending and want to get trailing notifications.
> + */
> + if ((msg->msg_flags & MSG_ZEROCOPY_UARG) &&
> + sock_flag(sk, SOCK_ZEROCOPY) && len == 0)
> + return 0;
> }
> if (!opt) {
> opt = txopt_get(np);
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index 16ff976a86e3..d6e6830f6ffe 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -84,7 +84,7 @@ static int virtio_transport_init_zcopy_skb(struct vsock_sock *vsk,
>
> uarg = msg_zerocopy_realloc(sk_vsock(vsk),
> iter->count,
> - NULL);
> + NULL, false);
> if (!uarg)
> return -1;
>
> --
> 2.20.1
>
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