new file mode 100644
--- /dev/null
+++ b/src/os/unix/ngx_udp_sendmsg_chain.c
@@ -0,0 +1,245 @@
+
+/*
+ * Copyright (C) Igor Sysoev
+ * Copyright (C) Nginx, Inc.
+ */
+
+
+#include <ngx_config.h>
+#include <ngx_core.h>
+#include <ngx_event.h>
+
+
+static ngx_chain_t *ngx_udp_output_chain_to_iovec(ngx_iovec_t *vec,
+    ngx_chain_t *in, ngx_log_t *log);
+static ssize_t ngx_sendmsg(ngx_connection_t *c, ngx_iovec_t *vec);
+
+
+ngx_chain_t *
+ngx_udp_unix_sendmsg_chain(ngx_connection_t *c, ngx_chain_t *in, off_t limit)
+{
+    ssize_t        n;
+    off_t          send;
+    ngx_chain_t   *cl;
+    ngx_event_t   *wev;
+    ngx_iovec_t    vec;
+    struct iovec   iovs[NGX_IOVS_PREALLOCATE];
+
+    wev = c->write;
+
+    if (!wev->ready) {
+        return in;
+    }
+
+#if (NGX_HAVE_KQUEUE)
+
+    if ((ngx_event_flags & NGX_USE_KQUEUE_EVENT) && wev->pending_eof) {
+        (void) ngx_connection_error(c, wev->kq_errno,
+                               "kevent() reported about an closed connection");
+        wev->error = 1;
+        return NGX_CHAIN_ERROR;
+    }
+
+#endif
+
+    /* the maximum limit size is the maximum size_t value - the page size */
+
+    if (limit == 0 || limit > (off_t) (NGX_MAX_SIZE_T_VALUE - ngx_pagesize)) {
+        limit = NGX_MAX_SIZE_T_VALUE - ngx_pagesize;
+    }
+
+    send = 0;
+
+    vec.iovs = iovs;
+    vec.nalloc = NGX_IOVS_PREALLOCATE;
+
+    for ( ;; ) {
+
+        /* create the iovec and coalesce the neighbouring bufs */
+
+        cl = ngx_udp_output_chain_to_iovec(&vec, in, c->log);
+
+        if (cl == NGX_CHAIN_ERROR) {
+            return NGX_CHAIN_ERROR;
+        }
+
+        if (cl && cl->buf->in_file) {
+            ngx_log_error(NGX_LOG_ALERT, c->log, 0,
+                          "file buf in sendmsg "
+                          "t:%d r:%d f:%d %p %p-%p %p %O-%O",
+                          cl->buf->temporary,
+                          cl->buf->recycled,
+                          cl->buf->in_file,
+                          cl->buf->start,
+                          cl->buf->pos,
+                          cl->buf->last,
+                          cl->buf->file,
+                          cl->buf->file_pos,
+                          cl->buf->file_last);
+
+            ngx_debug_point();
+
+            return NGX_CHAIN_ERROR;
+        }
+
+        if (cl == in) {
+            return in;
+        }
+
+        send += vec.size;
+
+        n = ngx_sendmsg(c, &vec);
+
+        if (n == NGX_ERROR) {
+            return NGX_CHAIN_ERROR;
+        }
+
+        if (n == NGX_AGAIN) {
+            wev->ready = 0;
+            return in;
+        }
+
+        c->sent += n;
+
+        in = ngx_chain_update_sent(in, n);
+
+        if (send >= limit || in == NULL) {
+            return in;
+        }
+    }
+}
+
+
+static ngx_chain_t *
+ngx_udp_output_chain_to_iovec(ngx_iovec_t *vec, ngx_chain_t *in, ngx_log_t *log)
+{
+    size_t         total, size;
+    u_char        *prev;
+    ngx_uint_t     n, flush;
+    ngx_chain_t   *cl;
+    struct iovec  *iov;
+
+    cl = in;
+    iov = NULL;
+    prev = NULL;
+    total = 0;
+    n = 0;
+    flush = 0;
+
+    for ( /* void */ ; in && !flush; in = in->next) {
+
+        if (in->buf->flush || in->buf->last_buf) {
+            flush = 1;
+        }
+
+        if (ngx_buf_special(in->buf)) {
+            continue;
+        }
+
+        if (in->buf->in_file) {
+            break;
+        }
+
+        if (!ngx_buf_in_memory(in->buf)) {
+            ngx_log_error(NGX_LOG_ALERT, log, 0,
+                          "bad buf in output chain "
+                          "t:%d r:%d f:%d %p %p-%p %p %O-%O",
+                          in->buf->temporary,
+                          in->buf->recycled,
+                          in->buf->in_file,
+                          in->buf->start,
+                          in->buf->pos,
+                          in->buf->last,
+                          in->buf->file,
+                          in->buf->file_pos,
+                          in->buf->file_last);
+
+            ngx_debug_point();
+
+            return NGX_CHAIN_ERROR;
+        }
+
+        size = in->buf->last - in->buf->pos;
+
+        if (prev == in->buf->pos) {
+            iov->iov_len += size;
+
+        } else {
+            if (n == vec->nalloc) {
+                ngx_log_error(NGX_LOG_ALERT, log, 0,
+                              "too many parts in a datagram");
+                return NGX_CHAIN_ERROR;
+            }
+
+            iov = &vec->iovs[n++];
+
+            iov->iov_base = (void *) in->buf->pos;
+            iov->iov_len = size;
+        }
+
+        prev = in->buf->pos + size;
+        total += size;
+    }
+
+    if (!flush) {
+#if (NGX_SUPPRESS_WARN)
+        vec->size = 0;
+        vec->count = 0;
+#endif
+        return cl;
+    }
+
+    vec->count = n;
+    vec->size = total;
+
+    return in;
+}
+
+
+static ssize_t
+ngx_sendmsg(ngx_connection_t *c, ngx_iovec_t *vec)
+{
+    ssize_t        n;
+    ngx_err_t      err;
+    struct msghdr  msg;
+
+    ngx_memzero(&msg, sizeof(struct msghdr));
+
+    if (c->socklen) {
+        msg.msg_name = c->sockaddr;
+        msg.msg_namelen = c->socklen;
+    }
+
+    msg.msg_iov = vec->iovs;
+    msg.msg_iovlen = vec->count;
+
+eintr:
+
+    n = sendmsg(c->fd, &msg, 0);
+
+    ngx_log_debug2(NGX_LOG_DEBUG_EVENT, c->log, 0,
+                   "sendmsg: %z of %uz", n, vec->size);
+
+    if (n == -1) {
+        err = ngx_errno;
+
+        switch (err) {
+        case NGX_EAGAIN:
+            ngx_log_debug0(NGX_LOG_DEBUG_EVENT, c->log, err,
+                           "sendmsg() not ready");
+            return NGX_AGAIN;
+
+        case NGX_EINTR:
+            ngx_log_debug0(NGX_LOG_DEBUG_EVENT, c->log, err,
+                           "sendmsg() was interrupted");
+            goto eintr;
+
+        default:
+            c->write->error = 1;
+            ngx_connection_error(c, err, "sendmsg() failed");
+            return NGX_ERROR;
+        }
+    }
+
+    return n;
+}