netlink: Split into generic and Linux-specific parts.

The parts of the netlink module that are related to sockets are
Linux-specific, since only Linux has AF_NETLINK sockets.  The rest can be
built anywhere.  This commit breaks them into two modules, and builds the
generic one on all platforms.

Acked-by: Jesse Gross <jesse@nicira.com>

10 files changed, 931 insertions, 841 deletions

diff --git a/lib/automake.mk b/lib/automake.mk
index 0d42e2097..a23a5696f 100644
--- a/lib/automake.mk
+++ b/lib/automake.mk
@@ -72,6 +72,8 @@ lib_libopenvswitch_a_SOURCES = \
 	lib/netdev-provider.h \
 	lib/netdev.c \
 	lib/netdev.h \
+	lib/netlink.c \
+	lib/netlink.h \
 	lib/nx-match.c \
 	lib/nx-match.def \
 	lib/nx-match.h \
@@ -182,8 +184,8 @@ lib_libopenvswitch_a_SOURCES += \
 	lib/netdev-vport.c \
 	lib/netdev-vport.h \
 	lib/netlink-protocol.h \
-	lib/netlink.c \
-	lib/netlink.h \
+	lib/netlink-socket.c \
+	lib/netlink-socket.h \
 	lib/rtnetlink.c \
 	lib/rtnetlink.h
 endif
diff --git a/lib/netdev-linux.c b/lib/netdev-linux.c
index b7447f8e9..ed97eb3c5 100644
--- a/lib/netdev-linux.c
+++ b/lib/netdev-linux.c
@@ -53,6 +53,7 @@
 #include "netdev-provider.h"
 #include "netdev-vport.h"
 #include "netlink.h"
+#include "netlink-socket.h"
 #include "ofpbuf.h"
 #include "openflow/openflow.h"
 #include "packets.h"
diff --git a/lib/netlink-socket.c b/lib/netlink-socket.c
new file mode 100644
index 000000000..c9402fd9f
--- /dev/null
+++ b/lib/netlink-socket.c
@@ -0,0 +1,814 @@
+/*
+ * Copyright (c) 2008, 2009, 2010 Nicira Networks.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <config.h>
+#include "netlink-socket.h"
+#include <assert.h>
+#include <errno.h>
+#include <inttypes.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include "coverage.h"
+#include "dynamic-string.h"
+#include "netlink.h"
+#include "netlink-protocol.h"
+#include "ofpbuf.h"
+#include "poll-loop.h"
+#include "stress.h"
+#include "vlog.h"
+
+VLOG_DEFINE_THIS_MODULE(netlink_socket);
+
+COVERAGE_DEFINE(netlink_overflow);
+COVERAGE_DEFINE(netlink_received);
+COVERAGE_DEFINE(netlink_recv_retry);
+COVERAGE_DEFINE(netlink_send);
+COVERAGE_DEFINE(netlink_sent);
+
+/* Linux header file confusion causes this to be undefined. */
+#ifndef SOL_NETLINK
+#define SOL_NETLINK 270
+#endif
+
+/* A single (bad) Netlink message can in theory dump out many, many log
+ * messages, so the burst size is set quite high here to avoid missing useful
+ * information.  Also, at high logging levels we log *all* Netlink messages. */
+static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(60, 600);
+
+static void log_nlmsg(const char *function, int error,
+                      const void *message, size_t size);
+
+/* Netlink sockets. */
+
+struct nl_sock
+{
+    int fd;
+    uint32_t pid;
+};
+
+static int alloc_pid(uint32_t *);
+static void free_pid(uint32_t);
+
+/* Creates a new netlink socket for the given netlink 'protocol'
+ * (NETLINK_ROUTE, NETLINK_GENERIC, ...).  Returns 0 and sets '*sockp' to the
+ * new socket if successful, otherwise returns a positive errno value.
+ *
+ * If 'multicast_group' is nonzero, the new socket subscribes to the specified
+ * netlink multicast group.  (A netlink socket may listen to an arbitrary
+ * number of multicast groups, but so far we only need one at a time.)
+ *
+ * Nonzero 'so_sndbuf' or 'so_rcvbuf' override the kernel default send or
+ * receive buffer size, respectively.
+ */
+int
+nl_sock_create(int protocol, int multicast_group,
+               size_t so_sndbuf, size_t so_rcvbuf, struct nl_sock **sockp)
+{
+    struct nl_sock *sock;
+    struct sockaddr_nl local, remote;
+    int retval = 0;
+
+    *sockp = NULL;
+    sock = malloc(sizeof *sock);
+    if (sock == NULL) {
+        return ENOMEM;
+    }
+
+    sock->fd = socket(AF_NETLINK, SOCK_RAW, protocol);
+    if (sock->fd < 0) {
+        VLOG_ERR("fcntl: %s", strerror(errno));
+        goto error;
+    }
+
+    retval = alloc_pid(&sock->pid);
+    if (retval) {
+        goto error;
+    }
+
+    if (so_sndbuf != 0
+        && setsockopt(sock->fd, SOL_SOCKET, SO_SNDBUF,
+                      &so_sndbuf, sizeof so_sndbuf) < 0) {
+        VLOG_ERR("setsockopt(SO_SNDBUF,%zu): %s", so_sndbuf, strerror(errno));
+        goto error_free_pid;
+    }
+
+    if (so_rcvbuf != 0
+        && setsockopt(sock->fd, SOL_SOCKET, SO_RCVBUF,
+                      &so_rcvbuf, sizeof so_rcvbuf) < 0) {
+        VLOG_ERR("setsockopt(SO_RCVBUF,%zu): %s", so_rcvbuf, strerror(errno));
+        goto error_free_pid;
+    }
+
+    /* Bind local address as our selected pid. */
+    memset(&local, 0, sizeof local);
+    local.nl_family = AF_NETLINK;
+    local.nl_pid = sock->pid;
+    if (multicast_group > 0 && multicast_group <= 32) {
+        /* This method of joining multicast groups is supported by old kernels,
+         * but it only allows 32 multicast groups per protocol. */
+        local.nl_groups |= 1ul << (multicast_group - 1);
+    }
+    if (bind(sock->fd, (struct sockaddr *) &local, sizeof local) < 0) {
+        VLOG_ERR("bind(%"PRIu32"): %s", sock->pid, strerror(errno));
+        goto error_free_pid;
+    }
+
+    /* Bind remote address as the kernel (pid 0). */
+    memset(&remote, 0, sizeof remote);
+    remote.nl_family = AF_NETLINK;
+    remote.nl_pid = 0;
+    if (connect(sock->fd, (struct sockaddr *) &remote, sizeof remote) < 0) {
+        VLOG_ERR("connect(0): %s", strerror(errno));
+        goto error_free_pid;
+    }
+
+    /* Older kernel headers failed to define this macro.  We want our programs
+     * to support the newer kernel features even if compiled with older
+     * headers, so define it ourselves in such a case. */
+#ifndef NETLINK_ADD_MEMBERSHIP
+#define NETLINK_ADD_MEMBERSHIP 1
+#endif
+
+    /* This method of joining multicast groups is only supported by newish
+     * kernels, but it allows for an arbitrary number of multicast groups. */
+    if (multicast_group > 32
+        && setsockopt(sock->fd, SOL_NETLINK, NETLINK_ADD_MEMBERSHIP,
+                      &multicast_group, sizeof multicast_group) < 0) {
+        VLOG_ERR("setsockopt(NETLINK_ADD_MEMBERSHIP,%d): %s",
+                 multicast_group, strerror(errno));
+        goto error_free_pid;
+    }
+
+    *sockp = sock;
+    return 0;
+
+error_free_pid:
+    free_pid(sock->pid);
+error:
+    if (retval == 0) {
+        retval = errno;
+        if (retval == 0) {
+            retval = EINVAL;
+        }
+    }
+    if (sock->fd >= 0) {
+        close(sock->fd);
+    }
+    free(sock);
+    return retval;
+}
+
+/* Destroys netlink socket 'sock'. */
+void
+nl_sock_destroy(struct nl_sock *sock)
+{
+    if (sock) {
+        close(sock->fd);
+        free_pid(sock->pid);
+        free(sock);
+    }
+}
+
+/* Tries to send 'msg', which must contain a Netlink message, to the kernel on
+ * 'sock'.  nlmsg_len in 'msg' will be finalized to match msg->size, and
+ * nlmsg_pid will be set to 'sock''s pid, before the message is sent.
+ *
+ * Returns 0 if successful, otherwise a positive errno value.  If
+ * 'wait' is true, then the send will wait until buffer space is ready;
+ * otherwise, returns EAGAIN if the 'sock' send buffer is full. */
+int
+nl_sock_send(struct nl_sock *sock, const struct ofpbuf *msg, bool wait)
+{
+    struct nlmsghdr *nlmsg = nl_msg_nlmsghdr(msg);
+    int error;
+
+    nlmsg->nlmsg_len = msg->size;
+    nlmsg->nlmsg_pid = sock->pid;
+    do {
+        int retval;
+        retval = send(sock->fd, msg->data, msg->size, wait ? 0 : MSG_DONTWAIT);
+        error = retval < 0 ? errno : 0;
+    } while (error == EINTR);
+    log_nlmsg(__func__, error, msg->data, msg->size);
+    if (!error) {
+        COVERAGE_INC(netlink_sent);
+    }
+    return error;
+}
+
+/* Tries to send the 'n_iov' chunks of data in 'iov' to the kernel on 'sock' as
+ * a single Netlink message.  (The message must be fully formed and not require
+ * finalization of its nlmsg_len or nlmsg_pid fields.)
+ *
+ * Returns 0 if successful, otherwise a positive errno value.  If 'wait' is
+ * true, then the send will wait until buffer space is ready; otherwise,
+ * returns EAGAIN if the 'sock' send buffer is full. */
+int
+nl_sock_sendv(struct nl_sock *sock, const struct iovec iov[], size_t n_iov,
+              bool wait)
+{
+    struct msghdr msg;
+    int error;
+
+    COVERAGE_INC(netlink_send);
+    memset(&msg, 0, sizeof msg);
+    msg.msg_iov = (struct iovec *) iov;
+    msg.msg_iovlen = n_iov;
+    do {
+        int retval;
+        retval = sendmsg(sock->fd, &msg, wait ? 0 : MSG_DONTWAIT);
+        error = retval < 0 ? errno : 0;
+    } while (error == EINTR);
+    if (error != EAGAIN) {
+        log_nlmsg(__func__, error, iov[0].iov_base, iov[0].iov_len);
+        if (!error) {
+            COVERAGE_INC(netlink_sent);
+        }
+    }
+    return error;
+}
+
+/* This stress option is useful for testing that OVS properly tolerates
+ * -ENOBUFS on NetLink sockets.  Such errors are unavoidable because they can
+ * occur if the kernel cannot temporarily allocate enough GFP_ATOMIC memory to
+ * reply to a request.  They can also occur if messages arrive on a multicast
+ * channel faster than OVS can process them. */
+STRESS_OPTION(
+    netlink_overflow, "simulate netlink socket receive buffer overflow",
+    5, 1, -1, 100);
+
+/* Tries to receive a netlink message from the kernel on 'sock'.  If
+ * successful, stores the received message into '*bufp' and returns 0.  The
+ * caller is responsible for destroying the message with ofpbuf_delete().  On
+ * failure, returns a positive errno value and stores a null pointer into
+ * '*bufp'.
+ *
+ * If 'wait' is true, nl_sock_recv waits for a message to be ready; otherwise,
+ * returns EAGAIN if the 'sock' receive buffer is empty. */
+int
+nl_sock_recv(struct nl_sock *sock, struct ofpbuf **bufp, bool wait)
+{
+    uint8_t tmp;
+    ssize_t bufsize = 2048;
+    ssize_t nbytes, nbytes2;
+    struct ofpbuf *buf;
+    struct nlmsghdr *nlmsghdr;
+    struct iovec iov;
+    struct msghdr msg = {
+        .msg_name = NULL,
+        .msg_namelen = 0,
+        .msg_iov = &iov,
+        .msg_iovlen = 1,
+        .msg_control = NULL,
+        .msg_controllen = 0,
+        .msg_flags = 0
+    };
+
+    buf = ofpbuf_new(bufsize);
+    *bufp = NULL;
+
+try_again:
+    /* Attempt to read the message.  We don't know the size of the data
+     * yet, so we take a guess at 2048.  If we're wrong, we keep trying
+     * and doubling the buffer size each time.
+     */
+    nlmsghdr = ofpbuf_put_uninit(buf, bufsize);
+    iov.iov_base = nlmsghdr;
+    iov.iov_len = bufsize;
+    do {
+        nbytes = recvmsg(sock->fd, &msg, (wait ? 0 : MSG_DONTWAIT) | MSG_PEEK);
+    } while (nbytes < 0 && errno == EINTR);
+    if (nbytes < 0) {
+        ofpbuf_delete(buf);
+        return errno;
+    }
+    if (msg.msg_flags & MSG_TRUNC) {
+        COVERAGE_INC(netlink_recv_retry);
+        bufsize *= 2;
+        ofpbuf_reinit(buf, bufsize);
+        goto try_again;
+    }
+    buf->size = nbytes;
+
+    /* We successfully read the message, so recv again to clear the queue */
+    iov.iov_base = &tmp;
+    iov.iov_len = 1;
+    do {
+        nbytes2 = recvmsg(sock->fd, &msg, MSG_DONTWAIT);
+    } while (nbytes2 < 0 && errno == EINTR);
+    if (nbytes2 < 0) {
+        if (errno == ENOBUFS) {
+            /* The kernel is notifying us that a message it tried to send to us
+             * was dropped.  We have to pass this along to the caller in case
+             * it wants to retry a request.  So kill the buffer, which we can
+             * re-read next time. */
+            COVERAGE_INC(netlink_overflow);
+            ofpbuf_delete(buf);
+            return ENOBUFS;
+        } else {
+            VLOG_ERR_RL(&rl, "failed to remove nlmsg from socket: %s\n",
+                        strerror(errno));
+        }
+    }
+    if (nbytes < sizeof *nlmsghdr
+        || nlmsghdr->nlmsg_len < sizeof *nlmsghdr
+        || nlmsghdr->nlmsg_len > nbytes) {
+        VLOG_ERR_RL(&rl, "received invalid nlmsg (%zd bytes < %d)",
+                    bufsize, NLMSG_HDRLEN);
+        ofpbuf_delete(buf);
+        return EPROTO;
+    }
+
+    if (STRESS(netlink_overflow)) {
+        ofpbuf_delete(buf);
+        return ENOBUFS;
+    }
+
+    *bufp = buf;
+    log_nlmsg(__func__, 0, buf->data, buf->size);
+    COVERAGE_INC(netlink_received);
+
+    return 0;
+}
+
+/* Sends 'request' to the kernel via 'sock' and waits for a response.  If
+ * successful, returns 0.  On failure, returns a positive errno value.
+ *
+ * If 'replyp' is nonnull, then on success '*replyp' is set to the kernel's
+ * reply, which the caller is responsible for freeing with ofpbuf_delete(), and
+ * on failure '*replyp' is set to NULL.  If 'replyp' is null, then the kernel's
+ * reply, if any, is discarded.
+ *
+ * nlmsg_len in 'msg' will be finalized to match msg->size, and nlmsg_pid will
+ * be set to 'sock''s pid, before the message is sent.  NLM_F_ACK will be set
+ * in nlmsg_flags.
+ *
+ * The caller is responsible for destroying 'request'.
+ *
+ * Bare Netlink is an unreliable transport protocol.  This function layers
+ * reliable delivery and reply semantics on top of bare Netlink.
+ *
+ * In Netlink, sending a request to the kernel is reliable enough, because the
+ * kernel will tell us if the message cannot be queued (and we will in that
+ * case put it on the transmit queue and wait until it can be delivered).
+ *
+ * Receiving the reply is the real problem: if the socket buffer is full when
+ * the kernel tries to send the reply, the reply will be dropped.  However, the
+ * kernel sets a flag that a reply has been dropped.  The next call to recv
+ * then returns ENOBUFS.  We can then re-send the request.
+ *
+ * Caveats:
+ *
+ *      1. Netlink depends on sequence numbers to match up requests and
+ *         replies.  The sender of a request supplies a sequence number, and
+ *         the reply echos back that sequence number.
+ *
+ *         This is fine, but (1) some kernel netlink implementations are
+ *         broken, in that they fail to echo sequence numbers and (2) this
+ *         function will drop packets with non-matching sequence numbers, so
+ *         that only a single request can be usefully transacted at a time.
+ *
+ *      2. Resending the request causes it to be re-executed, so the request
+ *         needs to be idempotent.
+ */
+int
+nl_sock_transact(struct nl_sock *sock,
+                 const struct ofpbuf *request, struct ofpbuf **replyp)
+{
+    uint32_t seq = nl_msg_nlmsghdr(request)->nlmsg_seq;
+    struct nlmsghdr *nlmsghdr;
+    struct ofpbuf *reply;
+    int retval;
+
+    if (replyp) {
+        *replyp = NULL;
+    }
+
+    /* Ensure that we get a reply even if this message doesn't ordinarily call
+     * for one. */
+    nl_msg_nlmsghdr(request)->nlmsg_flags |= NLM_F_ACK;
+
+send:
+    retval = nl_sock_send(sock, request, true);
+    if (retval) {
+        return retval;
+    }
+
+recv:
+    retval = nl_sock_recv(sock, &reply, true);
+    if (retval) {
+        if (retval == ENOBUFS) {
+            COVERAGE_INC(netlink_overflow);
+            VLOG_DBG_RL(&rl, "receive buffer overflow, resending request");
+            goto send;
+        } else {
+            return retval;
+        }
+    }
+    nlmsghdr = nl_msg_nlmsghdr(reply);
+    if (seq != nlmsghdr->nlmsg_seq) {
+        VLOG_DBG_RL(&rl, "ignoring seq %"PRIu32" != expected %"PRIu32,
+                    nl_msg_nlmsghdr(reply)->nlmsg_seq, seq);
+        ofpbuf_delete(reply);
+        goto recv;
+    }
+
+    /* If the reply is an error, discard the reply and return the error code.
+     *
+     * Except: if the reply is just an acknowledgement (error code of 0), and
+     * the caller is interested in the reply (replyp != NULL), pass the reply
+     * up to the caller.  Otherwise the caller will get a return value of 0
+     * and null '*replyp', which makes unwary callers likely to segfault. */
+    if (nl_msg_nlmsgerr(reply, &retval) && (retval || !replyp)) {
+        ofpbuf_delete(reply);
+        if (retval) {
+            VLOG_DBG_RL(&rl, "received NAK error=%d (%s)",
+                        retval, strerror(retval));
+        }
+        return retval != EAGAIN ? retval : EPROTO;
+    }
+
+    if (replyp) {
+        *replyp = reply;
+    } else {
+        ofpbuf_delete(reply);
+    }
+    return 0;
+}
+
+/* Starts a Netlink "dump" operation, by sending 'request' to the kernel via
+ * 'sock', and initializes 'dump' to reflect the state of the operation.
+ *
+ * nlmsg_len in 'msg' will be finalized to match msg->size, and nlmsg_pid will
+ * be set to 'sock''s pid, before the message is sent.  NLM_F_DUMP and
+ * NLM_F_ACK will be set in nlmsg_flags.
+ *
+ * The properties of Netlink make dump operations reliable as long as all of
+ * the following are true:
+ *
+ *   - At most a single dump is in progress at a time on a given nl_sock.
+ *
+ *   - The nl_sock is not subscribed to any multicast groups.
+ *
+ *   - The nl_sock is not used to send any other messages before the dump
+ *     operation is complete.
+ *
+ * This function provides no status indication.  An error status for the entire
+ * dump operation is provided when it is completed by calling nl_dump_done().
+ *
+ * The caller is responsible for destroying 'request'.  The caller must not
+ * close 'sock' before it completes the dump operation (by calling
+ * nl_dump_done()).
+ */
+void
+nl_dump_start(struct nl_dump *dump,
+              struct nl_sock *sock, const struct ofpbuf *request)
+{
+    struct nlmsghdr *nlmsghdr = nl_msg_nlmsghdr(request);
+    nlmsghdr->nlmsg_flags |= NLM_F_DUMP | NLM_F_ACK;
+    dump->seq = nlmsghdr->nlmsg_seq;
+    dump->sock = sock;
+    dump->status = nl_sock_send(sock, request, true);
+    dump->buffer = NULL;
+}
+
+/* Helper function for nl_dump_next(). */
+static int
+nl_dump_recv(struct nl_dump *dump, struct ofpbuf **bufferp)
+{
+    struct nlmsghdr *nlmsghdr;
+    struct ofpbuf *buffer;
+    int retval;
+
+    retval = nl_sock_recv(dump->sock, bufferp, true);
+    if (retval) {
+        return retval == EINTR ? EAGAIN : retval;
+    }
+    buffer = *bufferp;
+
+    nlmsghdr = nl_msg_nlmsghdr(buffer);
+    if (dump->seq != nlmsghdr->nlmsg_seq) {
+        VLOG_DBG_RL(&rl, "ignoring seq %"PRIu32" != expected %"PRIu32,
+                    nlmsghdr->nlmsg_seq, dump->seq);
+        return EAGAIN;
+    }
+
+    if (nl_msg_nlmsgerr(buffer, &retval)) {
+        VLOG_INFO_RL(&rl, "netlink dump request error (%s)",
+                     strerror(retval));
+        return retval && retval != EAGAIN ? retval : EPROTO;
+    }
+
+    return 0;
+}
+
+/* Attempts to retrieve another reply from 'dump', which must have been
+ * initialized with nl_dump_start().
+ *
+ * If successful, returns true and points 'reply->data' and 'reply->size' to
+ * the message that was retrieved.  The caller must not modify 'reply' (because
+ * it points into the middle of a larger buffer).
+ *
+ * On failure, returns false and sets 'reply->data' to NULL and 'reply->size'
+ * to 0.  Failure might indicate an actual error or merely the end of replies.
+ * An error status for the entire dump operation is provided when it is
+ * completed by calling nl_dump_done().
+ */
+bool
+nl_dump_next(struct nl_dump *dump, struct ofpbuf *reply)
+{
+    struct nlmsghdr *nlmsghdr;
+
+    reply->data = NULL;
+    reply->size = 0;
+    if (dump->status) {
+        return false;
+    }
+
+    if (dump->buffer && !dump->buffer->size) {
+        ofpbuf_delete(dump->buffer);
+        dump->buffer = NULL;
+    }
+    while (!dump->buffer) {
+        int retval = nl_dump_recv(dump, &dump->buffer);
+        if (retval) {
+            ofpbuf_delete(dump->buffer);
+            dump->buffer = NULL;
+            if (retval != EAGAIN) {
+                dump->status = retval;
+                return false;
+            }
+        }
+    }
+
+    nlmsghdr = nl_msg_next(dump->buffer, reply);
+    if (!nlmsghdr) {
+        VLOG_WARN_RL(&rl, "netlink dump reply contains message fragment");
+        dump->status = EPROTO;
+        return false;
+    } else if (nlmsghdr->nlmsg_type == NLMSG_DONE) {
+        dump->status = EOF;
+        return false;
+    }
+
+    return true;
+}
+
+/* Completes Netlink dump operation 'dump', which must have been initialized
+ * with nl_dump_start().  Returns 0 if the dump operation was error-free,
+ * otherwise a positive errno value describing the problem. */
+int
+nl_dump_done(struct nl_dump *dump)
+{
+    /* Drain any remaining messages that the client didn't read.  Otherwise the
+     * kernel will continue to queue them up and waste buffer space. */
+    while (!dump->status) {
+        struct ofpbuf reply;
+        if (!nl_dump_next(dump, &reply)) {
+            assert(dump->status);
+        }
+    }
+
+    ofpbuf_delete(dump->buffer);
+    return dump->status == EOF ? 0 : dump->status;
+}
+
+/* Causes poll_block() to wake up when any of the specified 'events' (which is
+ * a OR'd combination of POLLIN, POLLOUT, etc.) occur on 'sock'. */
+void
+nl_sock_wait(const struct nl_sock *sock, short int events)
+{
+    poll_fd_wait(sock->fd, events);
+}
+
+/* Miscellaneous.  */
+
+static const struct nl_policy family_policy[CTRL_ATTR_MAX + 1] = {
+    [CTRL_ATTR_FAMILY_ID] = {.type = NL_A_U16},
+};
+
+static int do_lookup_genl_family(const char *name)
+{
+    struct nl_sock *sock;
+    struct ofpbuf request, *reply;
+    struct nlattr *attrs[ARRAY_SIZE(family_policy)];
+    int retval;
+
+    retval = nl_sock_create(NETLINK_GENERIC, 0, 0, 0, &sock);
+    if (retval) {
+        return -retval;
+    }
+
+    ofpbuf_init(&request, 0);
+    nl_msg_put_genlmsghdr(&request, 0, GENL_ID_CTRL, NLM_F_REQUEST,
+                          CTRL_CMD_GETFAMILY, 1);
+    nl_msg_put_string(&request, CTRL_ATTR_FAMILY_NAME, name);
+    retval = nl_sock_transact(sock, &request, &reply);
+    ofpbuf_uninit(&request);
+    if (retval) {
+        nl_sock_destroy(sock);
+        return -retval;
+    }
+
+    if (!nl_policy_parse(reply, NLMSG_HDRLEN + GENL_HDRLEN,
+                         family_policy, attrs, ARRAY_SIZE(family_policy))) {
+        nl_sock_destroy(sock);
+        ofpbuf_delete(reply);
+        return -EPROTO;
+    }
+
+    retval = nl_attr_get_u16(attrs[CTRL_ATTR_FAMILY_ID]);
+    if (retval == 0) {
+        retval = -EPROTO;
+    }
+    nl_sock_destroy(sock);
+    ofpbuf_delete(reply);
+    return retval;
+}
+
+/* If '*number' is 0, translates the given Generic Netlink family 'name' to a
+ * number and stores it in '*number'.  If successful, returns 0 and the caller
+ * may use '*number' as the family number.  On failure, returns a positive
+ * errno value and '*number' caches the errno value. */
+int
+nl_lookup_genl_family(const char *name, int *number)
+{
+    if (*number == 0) {
+        *number = do_lookup_genl_family(name);
+        assert(*number != 0);
+    }
+    return *number > 0 ? 0 : -*number;
+}
+
+/* Netlink PID.
+ *
+ * Every Netlink socket must be bound to a unique 32-bit PID.  By convention,
+ * programs that have a single Netlink socket use their Unix process ID as PID,
+ * and programs with multiple Netlink sockets add a unique per-socket
+ * identifier in the bits above the Unix process ID.
+ *
+ * The kernel has Netlink PID 0.
+ */
+
+/* Parameters for how many bits in the PID should come from the Unix process ID
+ * and how many unique per-socket. */
+#define SOCKET_BITS 10
+#define MAX_SOCKETS (1u << SOCKET_BITS)
+
+#define PROCESS_BITS (32 - SOCKET_BITS)
+#define MAX_PROCESSES (1u << PROCESS_BITS)
+#define PROCESS_MASK ((uint32_t) (MAX_PROCESSES - 1))
+
+/* Bit vector of unused socket identifiers. */
+static uint32_t avail_sockets[ROUND_UP(MAX_SOCKETS, 32)];
+
+/* Allocates and returns a new Netlink PID. */
+static int
+alloc_pid(uint32_t *pid)
+{
+    int i;
+
+    for (i = 0; i < MAX_SOCKETS; i++) {
+        if ((avail_sockets[i / 32] & (1u << (i % 32))) == 0) {
+            avail_sockets[i / 32] |= 1u << (i % 32);
+            *pid = (getpid() & PROCESS_MASK) | (i << PROCESS_BITS);
+            return 0;
+        }
+    }
+    VLOG_ERR("netlink pid space exhausted");
+    return ENOBUFS;
+}
+
+/* Makes the specified 'pid' available for reuse. */
+static void
+free_pid(uint32_t pid)
+{
+    int sock = pid >> PROCESS_BITS;
+    assert(avail_sockets[sock / 32] & (1u << (sock % 32)));
+    avail_sockets[sock / 32] &= ~(1u << (sock % 32));
+}
+
+static void
+nlmsghdr_to_string(const struct nlmsghdr *h, struct ds *ds)
+{
+    struct nlmsg_flag {
+        unsigned int bits;
+        const char *name;
+    };
+    static const struct nlmsg_flag flags[] = {
+        { NLM_F_REQUEST, "REQUEST" },
+        { NLM_F_MULTI, "MULTI" },
+        { NLM_F_ACK, "ACK" },
+        { NLM_F_ECHO, "ECHO" },
+        { NLM_F_DUMP, "DUMP" },
+        { NLM_F_ROOT, "ROOT" },
+        { NLM_F_MATCH, "MATCH" },
+        { NLM_F_ATOMIC, "ATOMIC" },
+    };
+    const struct nlmsg_flag *flag;
+    uint16_t flags_left;
+
+    ds_put_format(ds, "nl(len:%"PRIu32", type=%"PRIu16,
+                  h->nlmsg_len, h->nlmsg_type);
+    if (h->nlmsg_type == NLMSG_NOOP) {
+        ds_put_cstr(ds, "(no-op)");
+    } else if (h->nlmsg_type == NLMSG_ERROR) {
+        ds_put_cstr(ds, "(error)");
+    } else if (h->nlmsg_type == NLMSG_DONE) {
+        ds_put_cstr(ds, "(done)");
+    } else if (h->nlmsg_type == NLMSG_OVERRUN) {
+        ds_put_cstr(ds, "(overrun)");
+    } else if (h->nlmsg_type < NLMSG_MIN_TYPE) {
+        ds_put_cstr(ds, "(reserved)");
+    } else {
+        ds_put_cstr(ds, "(family-defined)");
+    }
+    ds_put_format(ds, ", flags=%"PRIx16, h->nlmsg_flags);
+    flags_left = h->nlmsg_flags;
+    for (flag = flags; flag < &flags[ARRAY_SIZE(flags)]; flag++) {
+        if ((flags_left & flag->bits) == flag->bits) {
+            ds_put_format(ds, "[%s]", flag->name);
+            flags_left &= ~flag->bits;
+        }
+    }
+    if (flags_left) {
+        ds_put_format(ds, "[OTHER:%"PRIx16"]", flags_left);
+    }
+    ds_put_format(ds, ", seq=%"PRIx32", pid=%"PRIu32"(%d:%d))",
+                  h->nlmsg_seq, h->nlmsg_pid,
+                  (int) (h->nlmsg_pid & PROCESS_MASK),
+                  (int) (h->nlmsg_pid >> PROCESS_BITS));
+}
+
+static char *
+nlmsg_to_string(const struct ofpbuf *buffer)
+{
+    struct ds ds = DS_EMPTY_INITIALIZER;
+    const struct nlmsghdr *h = ofpbuf_at(buffer, 0, NLMSG_HDRLEN);
+    if (h) {
+        nlmsghdr_to_string(h, &ds);
+        if (h->nlmsg_type == NLMSG_ERROR) {
+            const struct nlmsgerr *e;
+            e = ofpbuf_at(buffer, NLMSG_HDRLEN,
+                          NLMSG_ALIGN(sizeof(struct nlmsgerr)));
+            if (e) {
+                ds_put_format(&ds, " error(%d", e->error);
+                if (e->error < 0) {
+                    ds_put_format(&ds, "(%s)", strerror(-e->error));
+                }
+                ds_put_cstr(&ds, ", in-reply-to(");
+                nlmsghdr_to_string(&e->msg, &ds);
+                ds_put_cstr(&ds, "))");
+            } else {
+                ds_put_cstr(&ds, " error(truncated)");
+            }
+        } else if (h->nlmsg_type == NLMSG_DONE) {
+            int *error = ofpbuf_at(buffer, NLMSG_HDRLEN, sizeof *error);
+            if (error) {
+                ds_put_format(&ds, " done(%d", *error);
+                if (*error < 0) {
+                    ds_put_format(&ds, "(%s)", strerror(-*error));
+                }
+                ds_put_cstr(&ds, ")");
+            } else {
+                ds_put_cstr(&ds, " done(truncated)");
+            }
+        }
+    } else {
+        ds_put_cstr(&ds, "nl(truncated)");
+    }
+    return ds.string;
+}
+
+static void
+log_nlmsg(const char *function, int error,
+          const void *message, size_t size)
+{
+    struct ofpbuf buffer;
+    char *nlmsg;
+
+    if (!VLOG_IS_DBG_ENABLED()) {
+        return;
+    }
+
+    ofpbuf_use_const(&buffer, message, size);
+    nlmsg = nlmsg_to_string(&buffer);
+    VLOG_DBG_RL(&rl, "%s (%s): %s", function, strerror(error), nlmsg);
+    free(nlmsg);
+}
+
+
diff --git a/lib/netlink-socket.h b/lib/netlink-socket.h
new file mode 100644
index 000000000..dc21ce838
--- /dev/null
+++ b/lib/netlink-socket.h
@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2008, 2009, 2010 Nicira Networks.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef NETLINK_SOCKET_H
+#define NETLINK_SOCKET_H 1
+
+/* Netlink socket definitions.
+ *
+ * Netlink is a datagram-based network protocol primarily for communication
+ * between user processes and the kernel, and mainly on Linux.  Netlink is
+ * specified in RFC 3549, "Linux Netlink as an IP Services Protocol".
+ *
+ * Netlink is not suitable for use in physical networks of heterogeneous
+ * machines because host byte order is used throughout.
+ *
+ * This header file defines functions for working with Netlink sockets, which
+ * are Linux-specific.  For Netlink protocol definitions, see
+ * netlink-protocol.h.  For helper functions for working with Netlink messages,
+ * see netlink.h.
+ */
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <sys/uio.h>
+
+struct ofpbuf;
+struct nl_sock;
+
+#ifndef HAVE_NETLINK
+#error "netlink-socket.h is only for hosts that support Netlink sockets"
+#endif
+
+/* Netlink sockets. */
+int nl_sock_create(int protocol, int multicast_group,
+                   size_t so_sndbuf, size_t so_rcvbuf,
+                   struct nl_sock **);
+void nl_sock_destroy(struct nl_sock *);
+
+int nl_sock_send(struct nl_sock *, const struct ofpbuf *, bool wait);
+int nl_sock_sendv(struct nl_sock *sock, const struct iovec iov[], size_t n_iov,
+                  bool wait);
+int nl_sock_recv(struct nl_sock *, struct ofpbuf **, bool wait);
+int nl_sock_transact(struct nl_sock *, const struct ofpbuf *request,
+                     struct ofpbuf **reply);
+
+void nl_sock_wait(const struct nl_sock *, short int events);
+
+/* Table dumping. */
+struct nl_dump {
+    struct nl_sock *sock;       /* Socket being dumped. */
+    uint32_t seq;               /* Expected nlmsg_seq for replies. */
+    struct ofpbuf *buffer;      /* Receive buffer currently being iterated. */
+    int status;                 /* 0=OK, EOF=done, or positive errno value. */
+};
+
+void nl_dump_start(struct nl_dump *, struct nl_sock *,
+                   const struct ofpbuf *request);
+bool nl_dump_next(struct nl_dump *, struct ofpbuf *reply);
+int nl_dump_done(struct nl_dump *);
+
+/* Miscellaneous */
+int nl_lookup_genl_family(const char *name, int *number);
+
+#endif /* netlink-socket.h */
diff --git a/lib/netlink.c b/lib/netlink.c
index f4af2527d..39d703aed 100644
--- a/lib/netlink.c
+++ b/lib/netlink.c
@@ -19,602 +19,21 @@
 #include <assert.h>
 #include <errno.h>
 #include <inttypes.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <time.h>
+#include <sys/types.h>
 #include <unistd.h>
 #include "coverage.h"
-#include "dynamic-string.h"
 #include "netlink-protocol.h"
 #include "ofpbuf.h"
-#include "poll-loop.h"
-#include "stress.h"
 #include "timeval.h"
-#include "util.h"
 #include "vlog.h"
 
 VLOG_DEFINE_THIS_MODULE(netlink);
 
-COVERAGE_DEFINE(netlink_overflow);
-COVERAGE_DEFINE(netlink_received);
-COVERAGE_DEFINE(netlink_recv_retry);
-COVERAGE_DEFINE(netlink_send);
-COVERAGE_DEFINE(netlink_sent);
-
-/* Linux header file confusion causes this to be undefined. */
-#ifndef SOL_NETLINK
-#define SOL_NETLINK 270
-#endif
-
 /* A single (bad) Netlink message can in theory dump out many, many log
  * messages, so the burst size is set quite high here to avoid missing useful
  * information.  Also, at high logging levels we log *all* Netlink messages. */
 static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(60, 600);
 
-static void log_nlmsg(const char *function, int error,
-                      const void *message, size_t size);
-
-/* Netlink sockets. */
-
-struct nl_sock
-{
-    int fd;
-    uint32_t pid;
-};
-
-/* Next nlmsghdr sequence number.
- *
- * This implementation uses sequence numbers that are unique process-wide, to
- * avoid a hypothetical race: send request, close socket, open new socket that
- * reuses the old socket's PID value, send request on new socket, receive reply
- * from kernel to old socket but with same PID and sequence number.  (This race
- * could be avoided other ways, e.g. by preventing PIDs from being quickly
- * reused). */
-static uint32_t next_seq;
-
-static int alloc_pid(uint32_t *);
-static void free_pid(uint32_t);
-
-/* Creates a new netlink socket for the given netlink 'protocol'
- * (NETLINK_ROUTE, NETLINK_GENERIC, ...).  Returns 0 and sets '*sockp' to the
- * new socket if successful, otherwise returns a positive errno value.
- *
- * If 'multicast_group' is nonzero, the new socket subscribes to the specified
- * netlink multicast group.  (A netlink socket may listen to an arbitrary
- * number of multicast groups, but so far we only need one at a time.)
- *
- * Nonzero 'so_sndbuf' or 'so_rcvbuf' override the kernel default send or
- * receive buffer size, respectively.
- */
-int
-nl_sock_create(int protocol, int multicast_group,
-               size_t so_sndbuf, size_t so_rcvbuf, struct nl_sock **sockp)
-{
-    struct nl_sock *sock;
-    struct sockaddr_nl local, remote;
-    int retval = 0;
-
-    if (next_seq == 0) {
-        /* Pick initial sequence number. */
-        next_seq = getpid() ^ time_wall();
-    }
-
-    *sockp = NULL;
-    sock = malloc(sizeof *sock);
-    if (sock == NULL) {
-        return ENOMEM;
-    }
-
-    sock->fd = socket(AF_NETLINK, SOCK_RAW, protocol);
-    if (sock->fd < 0) {
-        VLOG_ERR("fcntl: %s", strerror(errno));
-        goto error;
-    }
-
-    retval = alloc_pid(&sock->pid);
-    if (retval) {
-        goto error;
-    }
-
-    if (so_sndbuf != 0
-        && setsockopt(sock->fd, SOL_SOCKET, SO_SNDBUF,
-                      &so_sndbuf, sizeof so_sndbuf) < 0) {
-        VLOG_ERR("setsockopt(SO_SNDBUF,%zu): %s", so_sndbuf, strerror(errno));
-        goto error_free_pid;
-    }
-
-    if (so_rcvbuf != 0
-        && setsockopt(sock->fd, SOL_SOCKET, SO_RCVBUF,
-                      &so_rcvbuf, sizeof so_rcvbuf) < 0) {
-        VLOG_ERR("setsockopt(SO_RCVBUF,%zu): %s", so_rcvbuf, strerror(errno));
-        goto error_free_pid;
-    }
-
-    /* Bind local address as our selected pid. */
-    memset(&local, 0, sizeof local);
-    local.nl_family = AF_NETLINK;
-    local.nl_pid = sock->pid;
-    if (multicast_group > 0 && multicast_group <= 32) {
-        /* This method of joining multicast groups is supported by old kernels,
-         * but it only allows 32 multicast groups per protocol. */
-        local.nl_groups |= 1ul << (multicast_group - 1);
-    }
-    if (bind(sock->fd, (struct sockaddr *) &local, sizeof local) < 0) {
-        VLOG_ERR("bind(%"PRIu32"): %s", sock->pid, strerror(errno));
-        goto error_free_pid;
-    }
-
-    /* Bind remote address as the kernel (pid 0). */
-    memset(&remote, 0, sizeof remote);
-    remote.nl_family = AF_NETLINK;
-    remote.nl_pid = 0;
-    if (connect(sock->fd, (struct sockaddr *) &remote, sizeof remote) < 0) {
-        VLOG_ERR("connect(0): %s", strerror(errno));
-        goto error_free_pid;
-    }
-
-    /* Older kernel headers failed to define this macro.  We want our programs
-     * to support the newer kernel features even if compiled with older
-     * headers, so define it ourselves in such a case. */
-#ifndef NETLINK_ADD_MEMBERSHIP
-#define NETLINK_ADD_MEMBERSHIP 1
-#endif
-
-    /* This method of joining multicast groups is only supported by newish
-     * kernels, but it allows for an arbitrary number of multicast groups. */
-    if (multicast_group > 32
-        && setsockopt(sock->fd, SOL_NETLINK, NETLINK_ADD_MEMBERSHIP,
-                      &multicast_group, sizeof multicast_group) < 0) {
-        VLOG_ERR("setsockopt(NETLINK_ADD_MEMBERSHIP,%d): %s",
-                 multicast_group, strerror(errno));
-        goto error_free_pid;
-    }
-
-    *sockp = sock;
-    return 0;
-
-error_free_pid:
-    free_pid(sock->pid);
-error:
-    if (retval == 0) {
-        retval = errno;
-        if (retval == 0) {
-            retval = EINVAL;
-        }
-    }
-    if (sock->fd >= 0) {
-        close(sock->fd);
-    }
-    free(sock);
-    return retval;
-}
-
-/* Destroys netlink socket 'sock'. */
-void
-nl_sock_destroy(struct nl_sock *sock)
-{
-    if (sock) {
-        close(sock->fd);
-        free_pid(sock->pid);
-        free(sock);
-    }
-}
-
-/* Tries to send 'msg', which must contain a Netlink message, to the kernel on
- * 'sock'.  nlmsg_len in 'msg' will be finalized to match msg->size, and
- * nlmsg_pid will be set to 'sock''s pid, before the message is sent.
- *
- * Returns 0 if successful, otherwise a positive errno value.  If
- * 'wait' is true, then the send will wait until buffer space is ready;
- * otherwise, returns EAGAIN if the 'sock' send buffer is full. */
-int
-nl_sock_send(struct nl_sock *sock, const struct ofpbuf *msg, bool wait)
-{
-    struct nlmsghdr *nlmsg = nl_msg_nlmsghdr(msg);
-    int error;
-
-    nlmsg->nlmsg_len = msg->size;
-    nlmsg->nlmsg_pid = sock->pid;
-    do {
-        int retval;
-        retval = send(sock->fd, msg->data, msg->size, wait ? 0 : MSG_DONTWAIT);
-        error = retval < 0 ? errno : 0;
-    } while (error == EINTR);
-    log_nlmsg(__func__, error, msg->data, msg->size);
-    if (!error) {
-        COVERAGE_INC(netlink_sent);
-    }
-    return error;
-}
-
-/* Tries to send the 'n_iov' chunks of data in 'iov' to the kernel on 'sock' as
- * a single Netlink message.  (The message must be fully formed and not require
- * finalization of its nlmsg_len or nlmsg_pid fields.)
- *
- * Returns 0 if successful, otherwise a positive errno value.  If 'wait' is
- * true, then the send will wait until buffer space is ready; otherwise,
- * returns EAGAIN if the 'sock' send buffer is full. */
-int
-nl_sock_sendv(struct nl_sock *sock, const struct iovec iov[], size_t n_iov,
-              bool wait)
-{
-    struct msghdr msg;
-    int error;
-
-    COVERAGE_INC(netlink_send);
-    memset(&msg, 0, sizeof msg);
-    msg.msg_iov = (struct iovec *) iov;
-    msg.msg_iovlen = n_iov;
-    do {
-        int retval;
-        retval = sendmsg(sock->fd, &msg, wait ? 0 : MSG_DONTWAIT);
-        error = retval < 0 ? errno : 0;
-    } while (error == EINTR);
-    if (error != EAGAIN) {
-        log_nlmsg(__func__, error, iov[0].iov_base, iov[0].iov_len);
-        if (!error) {
-            COVERAGE_INC(netlink_sent);
-        }
-    }
-    return error;
-}
-
-/* This stress option is useful for testing that OVS properly tolerates
- * -ENOBUFS on NetLink sockets.  Such errors are unavoidable because they can
- * occur if the kernel cannot temporarily allocate enough GFP_ATOMIC memory to
- * reply to a request.  They can also occur if messages arrive on a multicast
- * channel faster than OVS can process them. */
-STRESS_OPTION(
-    netlink_overflow, "simulate netlink socket receive buffer overflow",
-    5, 1, -1, 100);
-
-/* Tries to receive a netlink message from the kernel on 'sock'.  If
- * successful, stores the received message into '*bufp' and returns 0.  The
- * caller is responsible for destroying the message with ofpbuf_delete().  On
- * failure, returns a positive errno value and stores a null pointer into
- * '*bufp'.
- *
- * If 'wait' is true, nl_sock_recv waits for a message to be ready; otherwise,
- * returns EAGAIN if the 'sock' receive buffer is empty. */
-int
-nl_sock_recv(struct nl_sock *sock, struct ofpbuf **bufp, bool wait)
-{
-    uint8_t tmp;
-    ssize_t bufsize = 2048;
-    ssize_t nbytes, nbytes2;
-    struct ofpbuf *buf;
-    struct nlmsghdr *nlmsghdr;
-    struct iovec iov;
-    struct msghdr msg = {
-        .msg_name = NULL,
-        .msg_namelen = 0,
-        .msg_iov = &iov,
-        .msg_iovlen = 1,
-        .msg_control = NULL,
-        .msg_controllen = 0,
-        .msg_flags = 0
-    };
-
-    buf = ofpbuf_new(bufsize);
-    *bufp = NULL;
-
-try_again:
-    /* Attempt to read the message.  We don't know the size of the data
-     * yet, so we take a guess at 2048.  If we're wrong, we keep trying
-     * and doubling the buffer size each time.
-     */
-    nlmsghdr = ofpbuf_put_uninit(buf, bufsize);
-    iov.iov_base = nlmsghdr;
-    iov.iov_len = bufsize;
-    do {
-        nbytes = recvmsg(sock->fd, &msg, (wait ? 0 : MSG_DONTWAIT) | MSG_PEEK);
-    } while (nbytes < 0 && errno == EINTR);
-    if (nbytes < 0) {
-        ofpbuf_delete(buf);
-        return errno;
-    }
-    if (msg.msg_flags & MSG_TRUNC) {
-        COVERAGE_INC(netlink_recv_retry);
-        bufsize *= 2;
-        ofpbuf_reinit(buf, bufsize);
-        goto try_again;
-    }
-    buf->size = nbytes;
-
-    /* We successfully read the message, so recv again to clear the queue */
-    iov.iov_base = &tmp;
-    iov.iov_len = 1;
-    do {
-        nbytes2 = recvmsg(sock->fd, &msg, MSG_DONTWAIT);
-    } while (nbytes2 < 0 && errno == EINTR);
-    if (nbytes2 < 0) {
-        if (errno == ENOBUFS) {
-            /* The kernel is notifying us that a message it tried to send to us
-             * was dropped.  We have to pass this along to the caller in case
-             * it wants to retry a request.  So kill the buffer, which we can
-             * re-read next time. */
-            COVERAGE_INC(netlink_overflow);
-            ofpbuf_delete(buf);
-            return ENOBUFS;
-        } else {
-            VLOG_ERR_RL(&rl, "failed to remove nlmsg from socket: %s\n",
-                        strerror(errno));
-        }
-    }
-    if (nbytes < sizeof *nlmsghdr
-        || nlmsghdr->nlmsg_len < sizeof *nlmsghdr
-        || nlmsghdr->nlmsg_len > nbytes) {
-        VLOG_ERR_RL(&rl, "received invalid nlmsg (%zd bytes < %d)",
-                    bufsize, NLMSG_HDRLEN);
-        ofpbuf_delete(buf);
-        return EPROTO;
-    }
-
-    if (STRESS(netlink_overflow)) {
-        ofpbuf_delete(buf);
-        return ENOBUFS;
-    }
-
-    *bufp = buf;
-    log_nlmsg(__func__, 0, buf->data, buf->size);
-    COVERAGE_INC(netlink_received);
-
-    return 0;
-}
-
-/* Sends 'request' to the kernel via 'sock' and waits for a response.  If
- * successful, returns 0.  On failure, returns a positive errno value.
- *
- * If 'replyp' is nonnull, then on success '*replyp' is set to the kernel's
- * reply, which the caller is responsible for freeing with ofpbuf_delete(), and
- * on failure '*replyp' is set to NULL.  If 'replyp' is null, then the kernel's
- * reply, if any, is discarded.
- *
- * nlmsg_len in 'msg' will be finalized to match msg->size, and nlmsg_pid will
- * be set to 'sock''s pid, before the message is sent.  NLM_F_ACK will be set
- * in nlmsg_flags.
- *
- * The caller is responsible for destroying 'request'.
- *
- * Bare Netlink is an unreliable transport protocol.  This function layers
- * reliable delivery and reply semantics on top of bare Netlink.
- *
- * In Netlink, sending a request to the kernel is reliable enough, because the
- * kernel will tell us if the message cannot be queued (and we will in that
- * case put it on the transmit queue and wait until it can be delivered).
- *
- * Receiving the reply is the real problem: if the socket buffer is full when
- * the kernel tries to send the reply, the reply will be dropped.  However, the
- * kernel sets a flag that a reply has been dropped.  The next call to recv
- * then returns ENOBUFS.  We can then re-send the request.
- *
- * Caveats:
- *
- *      1. Netlink depends on sequence numbers to match up requests and
- *         replies.  The sender of a request supplies a sequence number, and
- *         the reply echos back that sequence number.
- *
- *         This is fine, but (1) some kernel netlink implementations are
- *         broken, in that they fail to echo sequence numbers and (2) this
- *         function will drop packets with non-matching sequence numbers, so
- *         that only a single request can be usefully transacted at a time.
- *
- *      2. Resending the request causes it to be re-executed, so the request
- *         needs to be idempotent.
- */
-int
-nl_sock_transact(struct nl_sock *sock,
-                 const struct ofpbuf *request, struct ofpbuf **replyp)
-{
-    uint32_t seq = nl_msg_nlmsghdr(request)->nlmsg_seq;
-    struct nlmsghdr *nlmsghdr;
-    struct ofpbuf *reply;
-    int retval;
-
-    if (replyp) {
-        *replyp = NULL;
-    }
-
-    /* Ensure that we get a reply even if this message doesn't ordinarily call
-     * for one. */
-    nl_msg_nlmsghdr(request)->nlmsg_flags |= NLM_F_ACK;
-
-send:
-    retval = nl_sock_send(sock, request, true);
-    if (retval) {
-        return retval;
-    }
-
-recv:
-    retval = nl_sock_recv(sock, &reply, true);
-    if (retval) {
-        if (retval == ENOBUFS) {
-            COVERAGE_INC(netlink_overflow);
-            VLOG_DBG_RL(&rl, "receive buffer overflow, resending request");
-            goto send;
-        } else {
-            return retval;
-        }
-    }
-    nlmsghdr = nl_msg_nlmsghdr(reply);
-    if (seq != nlmsghdr->nlmsg_seq) {
-        VLOG_DBG_RL(&rl, "ignoring seq %"PRIu32" != expected %"PRIu32,
-                    nl_msg_nlmsghdr(reply)->nlmsg_seq, seq);
-        ofpbuf_delete(reply);
-        goto recv;
-    }
-
-    /* If the reply is an error, discard the reply and return the error code.
-     *
-     * Except: if the reply is just an acknowledgement (error code of 0), and
-     * the caller is interested in the reply (replyp != NULL), pass the reply
-     * up to the caller.  Otherwise the caller will get a return value of 0
-     * and null '*replyp', which makes unwary callers likely to segfault. */
-    if (nl_msg_nlmsgerr(reply, &retval) && (retval || !replyp)) {
-        ofpbuf_delete(reply);
-        if (retval) {
-            VLOG_DBG_RL(&rl, "received NAK error=%d (%s)",
-                        retval, strerror(retval));
-        }
-        return retval != EAGAIN ? retval : EPROTO;
-    }
-
-    if (replyp) {
-        *replyp = reply;
-    } else {
-        ofpbuf_delete(reply);
-    }
-    return 0;
-}
-
-/* Starts a Netlink "dump" operation, by sending 'request' to the kernel via
- * 'sock', and initializes 'dump' to reflect the state of the operation.
- *
- * nlmsg_len in 'msg' will be finalized to match msg->size, and nlmsg_pid will
- * be set to 'sock''s pid, before the message is sent.  NLM_F_DUMP and
- * NLM_F_ACK will be set in nlmsg_flags.
- *
- * The properties of Netlink make dump operations reliable as long as all of
- * the following are true:
- *
- *   - At most a single dump is in progress at a time on a given nl_sock.
- *
- *   - The nl_sock is not subscribed to any multicast groups.
- *
- *   - The nl_sock is not used to send any other messages before the dump
- *     operation is complete.
- *
- * This function provides no status indication.  An error status for the entire
- * dump operation is provided when it is completed by calling nl_dump_done().
- *
- * The caller is responsible for destroying 'request'.  The caller must not
- * close 'sock' before it completes the dump operation (by calling
- * nl_dump_done()).
- */
-void
-nl_dump_start(struct nl_dump *dump,
-              struct nl_sock *sock, const struct ofpbuf *request)
-{
-    struct nlmsghdr *nlmsghdr = nl_msg_nlmsghdr(request);
-    nlmsghdr->nlmsg_flags |= NLM_F_DUMP | NLM_F_ACK;
-    dump->seq = nlmsghdr->nlmsg_seq;
-    dump->sock = sock;
-    dump->status = nl_sock_send(sock, request, true);
-    dump->buffer = NULL;
-}
-
-/* Helper function for nl_dump_next(). */
-static int
-nl_dump_recv(struct nl_dump *dump, struct ofpbuf **bufferp)
-{
-    struct nlmsghdr *nlmsghdr;
-    struct ofpbuf *buffer;
-    int retval;
-
-    retval = nl_sock_recv(dump->sock, bufferp, true);
-    if (retval) {
-        return retval == EINTR ? EAGAIN : retval;
-    }
-    buffer = *bufferp;
-
-    nlmsghdr = nl_msg_nlmsghdr(buffer);
-    if (dump->seq != nlmsghdr->nlmsg_seq) {
-        VLOG_DBG_RL(&rl, "ignoring seq %"PRIu32" != expected %"PRIu32,
-                    nlmsghdr->nlmsg_seq, dump->seq);
-        return EAGAIN;
-    }
-
-    if (nl_msg_nlmsgerr(buffer, &retval)) {
-        VLOG_INFO_RL(&rl, "netlink dump request error (%s)",
-                     strerror(retval));
-        return retval && retval != EAGAIN ? retval : EPROTO;
-    }
-
-    return 0;
-}
-
-/* Attempts to retrieve another reply from 'dump', which must have been
- * initialized with nl_dump_start().
- *
- * If successful, returns true and points 'reply->data' and 'reply->size' to
- * the message that was retrieved.  The caller must not modify 'reply' (because
- * it points into the middle of a larger buffer).
- *
- * On failure, returns false and sets 'reply->data' to NULL and 'reply->size'
- * to 0.  Failure might indicate an actual error or merely the end of replies.
- * An error status for the entire dump operation is provided when it is
- * completed by calling nl_dump_done().
- */
-bool
-nl_dump_next(struct nl_dump *dump, struct ofpbuf *reply)
-{
-    struct nlmsghdr *nlmsghdr;
-
-    reply->data = NULL;
-    reply->size = 0;
-    if (dump->status) {
-        return false;
-    }
-
-    if (dump->buffer && !dump->buffer->size) {
-        ofpbuf_delete(dump->buffer);
-        dump->buffer = NULL;
-    }
-    while (!dump->buffer) {
-        int retval = nl_dump_recv(dump, &dump->buffer);
-        if (retval) {
-            ofpbuf_delete(dump->buffer);
-            dump->buffer = NULL;
-            if (retval != EAGAIN) {
-                dump->status = retval;
-                return false;
-            }
-        }
-    }
-
-    nlmsghdr = nl_msg_next(dump->buffer, reply);
-    if (!nlmsghdr) {
-        VLOG_WARN_RL(&rl, "netlink dump reply contains message fragment");
-        dump->status = EPROTO;
-        return false;
-    } else if (nlmsghdr->nlmsg_type == NLMSG_DONE) {
-        dump->status = EOF;
-        return false;
-    }
-
-    return true;
-}
-
-/* Completes Netlink dump operation 'dump', which must have been initialized
- * with nl_dump_start().  Returns 0 if the dump operation was error-free,
- * otherwise a positive errno value describing the problem. */
-int
-nl_dump_done(struct nl_dump *dump)
-{
-    /* Drain any remaining messages that the client didn't read.  Otherwise the
-     * kernel will continue to queue them up and waste buffer space. */
-    while (!dump->status) {
-        struct ofpbuf reply;
-        if (!nl_dump_next(dump, &reply)) {
-            assert(dump->status);
-        }
-    }
-
-    ofpbuf_delete(dump->buffer);
-    return dump->status == EOF ? 0 : dump->status;
-}
-
-/* Causes poll_block() to wake up when any of the specified 'events' (which is
- * a OR'd combination of POLLIN, POLLOUT, etc.) occur on 'sock'. */
-void
-nl_sock_wait(const struct nl_sock *sock, short int events)
-{
-    poll_fd_wait(sock->fd, events);
-}
-
-/* Netlink messages. */
-
 /* Returns the nlmsghdr at the head of 'msg'.
  *
  * 'msg' must be at least as large as a nlmsghdr. */
@@ -668,6 +87,26 @@ nl_msg_reserve(struct ofpbuf *msg, size_t size)
     ofpbuf_prealloc_tailroom(msg, NLMSG_ALIGN(size));
 }
 
+static uint32_t
+get_nlmsg_seq(void)
+{
+    /* Next nlmsghdr sequence number.
+     *
+     * This implementation uses sequence numbers that are unique process-wide,
+     * to avoid a hypothetical race: send request, close socket, open new
+     * socket that reuses the old socket's PID value, send request on new
+     * socket, receive reply from kernel to old socket but with same PID and
+     * sequence number.  (This race could be avoided other ways, e.g. by
+     * preventing PIDs from being quickly reused). */
+    static uint32_t next_seq;
+
+    if (next_seq == 0) {
+        /* Pick initial sequence number. */
+        next_seq = getpid() ^ time_wall();
+    }
+    return next_seq++;
+}
+
 /* Puts a nlmsghdr at the beginning of 'msg', which must be initially empty.
  * Uses the given 'type' and 'flags'.  'expected_payload' should be
  * an estimate of the number of payload bytes to be supplied; if the size of
@@ -699,7 +138,7 @@ nl_msg_put_nlmsghdr(struct ofpbuf *msg,
     nlmsghdr->nlmsg_len = 0;
     nlmsghdr->nlmsg_type = type;
     nlmsghdr->nlmsg_flags = flags;
-    nlmsghdr->nlmsg_seq = ++next_seq;
+    nlmsghdr->nlmsg_seq = get_nlmsg_seq();
     nlmsghdr->nlmsg_pid = 0;
 }
 
@@ -1110,220 +549,3 @@ nl_parse_nested(const struct nlattr *nla, const struct nl_policy policy[],
     nl_attr_get_nested(nla, &buf);
     return nl_policy_parse(&buf, 0, policy, attrs, n_attrs);
 }
-
-/* Miscellaneous.  */
-
-static const struct nl_policy family_policy[CTRL_ATTR_MAX + 1] = {
-    [CTRL_ATTR_FAMILY_ID] = {.type = NL_A_U16},
-};
-
-static int do_lookup_genl_family(const char *name)
-{
-    struct nl_sock *sock;
-    struct ofpbuf request, *reply;
-    struct nlattr *attrs[ARRAY_SIZE(family_policy)];
-    int retval;
-
-    retval = nl_sock_create(NETLINK_GENERIC, 0, 0, 0, &sock);
-    if (retval) {
-        return -retval;
-    }
-
-    ofpbuf_init(&request, 0);
-    nl_msg_put_genlmsghdr(&request, 0, GENL_ID_CTRL, NLM_F_REQUEST,
-                          CTRL_CMD_GETFAMILY, 1);
-    nl_msg_put_string(&request, CTRL_ATTR_FAMILY_NAME, name);
-    retval = nl_sock_transact(sock, &request, &reply);
-    ofpbuf_uninit(&request);
-    if (retval) {
-        nl_sock_destroy(sock);
-        return -retval;
-    }
-
-    if (!nl_policy_parse(reply, NLMSG_HDRLEN + GENL_HDRLEN,
-                         family_policy, attrs, ARRAY_SIZE(family_policy))) {
-        nl_sock_destroy(sock);
-        ofpbuf_delete(reply);
-        return -EPROTO;
-    }
-
-    retval = nl_attr_get_u16(attrs[CTRL_ATTR_FAMILY_ID]);
-    if (retval == 0) {
-        retval = -EPROTO;
-    }
-    nl_sock_destroy(sock);
-    ofpbuf_delete(reply);
-    return retval;
-}
-
-/* If '*number' is 0, translates the given Generic Netlink family 'name' to a
- * number and stores it in '*number'.  If successful, returns 0 and the caller
- * may use '*number' as the family number.  On failure, returns a positive
- * errno value and '*number' caches the errno value. */
-int
-nl_lookup_genl_family(const char *name, int *number)
-{
-    if (*number == 0) {
-        *number = do_lookup_genl_family(name);
-        assert(*number != 0);
-    }
-    return *number > 0 ? 0 : -*number;
-}
-
-/* Netlink PID.
- *
- * Every Netlink socket must be bound to a unique 32-bit PID.  By convention,
- * programs that have a single Netlink socket use their Unix process ID as PID,
- * and programs with multiple Netlink sockets add a unique per-socket
- * identifier in the bits above the Unix process ID.
- *
- * The kernel has Netlink PID 0.
- */
-
-/* Parameters for how many bits in the PID should come from the Unix process ID
- * and how many unique per-socket. */
-#define SOCKET_BITS 10
-#define MAX_SOCKETS (1u << SOCKET_BITS)
-
-#define PROCESS_BITS (32 - SOCKET_BITS)
-#define MAX_PROCESSES (1u << PROCESS_BITS)
-#define PROCESS_MASK ((uint32_t) (MAX_PROCESSES - 1))
-
-/* Bit vector of unused socket identifiers. */
-static uint32_t avail_sockets[ROUND_UP(MAX_SOCKETS, 32)];
-
-/* Allocates and returns a new Netlink PID. */
-static int
-alloc_pid(uint32_t *pid)
-{
-    int i;
-
-    for (i = 0; i < MAX_SOCKETS; i++) {
-        if ((avail_sockets[i / 32] & (1u << (i % 32))) == 0) {
-            avail_sockets[i / 32] |= 1u << (i % 32);
-            *pid = (getpid() & PROCESS_MASK) | (i << PROCESS_BITS);
-            return 0;
-        }
-    }
-    VLOG_ERR("netlink pid space exhausted");
-    return ENOBUFS;
-}
-
-/* Makes the specified 'pid' available for reuse. */
-static void
-free_pid(uint32_t pid)
-{
-    int sock = pid >> PROCESS_BITS;
-    assert(avail_sockets[sock / 32] & (1u << (sock % 32)));
-    avail_sockets[sock / 32] &= ~(1u << (sock % 32));
-}
-
-static void
-nlmsghdr_to_string(const struct nlmsghdr *h, struct ds *ds)
-{
-    struct nlmsg_flag {
-        unsigned int bits;
-        const char *name;
-    };
-    static const struct nlmsg_flag flags[] = {
-        { NLM_F_REQUEST, "REQUEST" },
-        { NLM_F_MULTI, "MULTI" },
-        { NLM_F_ACK, "ACK" },
-        { NLM_F_ECHO, "ECHO" },
-        { NLM_F_DUMP, "DUMP" },
-        { NLM_F_ROOT, "ROOT" },
-        { NLM_F_MATCH, "MATCH" },
-        { NLM_F_ATOMIC, "ATOMIC" },
-    };
-    const struct nlmsg_flag *flag;
-    uint16_t flags_left;
-
-    ds_put_format(ds, "nl(len:%"PRIu32", type=%"PRIu16,
-                  h->nlmsg_len, h->nlmsg_type);
-    if (h->nlmsg_type == NLMSG_NOOP) {
-        ds_put_cstr(ds, "(no-op)");
-    } else if (h->nlmsg_type == NLMSG_ERROR) {
-        ds_put_cstr(ds, "(error)");
-    } else if (h->nlmsg_type == NLMSG_DONE) {
-        ds_put_cstr(ds, "(done)");
-    } else if (h->nlmsg_type == NLMSG_OVERRUN) {
-        ds_put_cstr(ds, "(overrun)");
-    } else if (h->nlmsg_type < NLMSG_MIN_TYPE) {
-        ds_put_cstr(ds, "(reserved)");
-    } else {
-        ds_put_cstr(ds, "(family-defined)");
-    }
-    ds_put_format(ds, ", flags=%"PRIx16, h->nlmsg_flags);
-    flags_left = h->nlmsg_flags;
-    for (flag = flags; flag < &flags[ARRAY_SIZE(flags)]; flag++) {
-        if ((flags_left & flag->bits) == flag->bits) {
-            ds_put_format(ds, "[%s]", flag->name);
-            flags_left &= ~flag->bits;
-        }
-    }
-    if (flags_left) {
-        ds_put_format(ds, "[OTHER:%"PRIx16"]", flags_left);
-    }
-    ds_put_format(ds, ", seq=%"PRIx32", pid=%"PRIu32"(%d:%d))",
-                  h->nlmsg_seq, h->nlmsg_pid,
-                  (int) (h->nlmsg_pid & PROCESS_MASK),
-                  (int) (h->nlmsg_pid >> PROCESS_BITS));
-}
-
-static char *
-nlmsg_to_string(const struct ofpbuf *buffer)
-{
-    struct ds ds = DS_EMPTY_INITIALIZER;
-    const struct nlmsghdr *h = ofpbuf_at(buffer, 0, NLMSG_HDRLEN);
-    if (h) {
-        nlmsghdr_to_string(h, &ds);
-        if (h->nlmsg_type == NLMSG_ERROR) {
-            const struct nlmsgerr *e;
-            e = ofpbuf_at(buffer, NLMSG_HDRLEN,
-                          NLMSG_ALIGN(sizeof(struct nlmsgerr)));
-            if (e) {
-                ds_put_format(&ds, " error(%d", e->error);
-                if (e->error < 0) {
-                    ds_put_format(&ds, "(%s)", strerror(-e->error));
-                }
-                ds_put_cstr(&ds, ", in-reply-to(");
-                nlmsghdr_to_string(&e->msg, &ds);
-                ds_put_cstr(&ds, "))");
-            } else {
-                ds_put_cstr(&ds, " error(truncated)");
-            }
-        } else if (h->nlmsg_type == NLMSG_DONE) {
-            int *error = ofpbuf_at(buffer, NLMSG_HDRLEN, sizeof *error);
-            if (error) {
-                ds_put_format(&ds, " done(%d", *error);
-                if (*error < 0) {
-                    ds_put_format(&ds, "(%s)", strerror(-*error));
-                }
-                ds_put_cstr(&ds, ")");
-            } else {
-                ds_put_cstr(&ds, " done(truncated)");
-            }
-        }
-    } else {
-        ds_put_cstr(&ds, "nl(truncated)");
-    }
-    return ds.string;
-}
-
-static void
-log_nlmsg(const char *function, int error,
-          const void *message, size_t size)
-{
-    struct ofpbuf buffer;
-    char *nlmsg;
-
-    if (!VLOG_IS_DBG_ENABLED()) {
-        return;
-    }
-
-    ofpbuf_use_const(&buffer, message, size);
-    nlmsg = nlmsg_to_string(&buffer);
-    VLOG_DBG_RL(&rl, "%s (%s): %s", function, strerror(error), nlmsg);
-    free(nlmsg);
-}
-
diff --git a/lib/netlink.h b/lib/netlink.h
index 9cb1f8103..127a41b7b 100644
--- a/lib/netlink.h
+++ b/lib/netlink.h
@@ -17,54 +17,27 @@
 #ifndef NETLINK_H
 #define NETLINK_H 1
 
-/* Netlink interface.
+/* Netlink message helpers.
  *
  * Netlink is a datagram-based network protocol primarily for communication
  * between user processes and the kernel, and mainly on Linux.  Netlink is
  * specified in RFC 3549, "Linux Netlink as an IP Services Protocol".
  *
  * Netlink is not suitable for use in physical networks of heterogeneous
- * machines because host byte order is used throughout. */
+ * machines because host byte order is used throughout.
+ *
+ * This header file defines helper functions for working with Netlink messages.
+ * For Netlink protocol definitions, see netlink-protocol.h.  For
+ * Linux-specific definitions for Netlink sockets, see netlink-socket.h.
+ */
 
 #include <stdbool.h>
-#include <sys/uio.h>
+#include <stddef.h>
 #include <stdint.h>
 
 struct ofpbuf;
-struct nl_sock;
 struct nlattr;
 
-/* Netlink sockets. */
-
-int nl_sock_create(int protocol, int multicast_group,
-                   size_t so_sndbuf, size_t so_rcvbuf,
-                   struct nl_sock **);
-void nl_sock_destroy(struct nl_sock *);
-
-int nl_sock_send(struct nl_sock *, const struct ofpbuf *, bool wait);
-int nl_sock_sendv(struct nl_sock *sock, const struct iovec iov[], size_t n_iov,
-                  bool wait);
-int nl_sock_recv(struct nl_sock *, struct ofpbuf **, bool wait);
-int nl_sock_transact(struct nl_sock *, const struct ofpbuf *request,
-                     struct ofpbuf **reply);
-
-void nl_sock_wait(const struct nl_sock *, short int events);
-
-/* Table dumping. */
-struct nl_dump {
-    struct nl_sock *sock;       /* Socket being dumped. */
-    uint32_t seq;               /* Expected nlmsg_seq for replies. */
-    struct ofpbuf *buffer;      /* Receive buffer currently being iterated. */
-    int status;                 /* 0=OK, EOF=done, or positive errno value. */
-};
-
-void nl_dump_start(struct nl_dump *, struct nl_sock *,
-                   const struct ofpbuf *request);
-bool nl_dump_next(struct nl_dump *, struct ofpbuf *reply);
-int nl_dump_done(struct nl_dump *);
-
-/* Netlink messages. */
-
 /* Accessing headers and data. */
 struct nlmsghdr *nl_msg_nlmsghdr(const struct ofpbuf *);
 struct genlmsghdr *nl_msg_genlmsghdr(const struct ofpbuf *);
@@ -141,9 +114,5 @@ bool nl_policy_parse(const struct ofpbuf *, size_t offset,
                      struct nlattr *[], size_t n_attrs);
 bool nl_parse_nested(const struct nlattr *, const struct nl_policy[],
                      struct nlattr *[], size_t n_attrs);
-
-/* Miscellaneous. */
-
-int nl_lookup_genl_family(const char *name, int *number);
 
 #endif /* netlink.h */
diff --git a/lib/rtnetlink.c b/lib/rtnetlink.c
index 9beddb139..54340e5c0 100644
--- a/lib/rtnetlink.c
+++ b/lib/rtnetlink.c
@@ -26,6 +26,7 @@
 
 #include "coverage.h"
 #include "netlink.h"
+#include "netlink-socket.h"
 #include "ofpbuf.h"
 #include "vlog.h"
 
diff --git a/utilities/nlmon.c b/utilities/nlmon.c
index 672fae47a..1fb380808 100644
--- a/utilities/nlmon.c
+++ b/utilities/nlmon.c
@@ -24,6 +24,7 @@
 #include <stddef.h>
 #include <linux/rtnetlink.h>
 #include "netlink.h"
+#include "netlink-socket.h"
 #include "ofpbuf.h"
 #include "poll-loop.h"
 #include "timeval.h"
diff --git a/vswitchd/ovs-brcompatd.c b/vswitchd/ovs-brcompatd.c
index ecf00b3d2..bed274742 100644
--- a/vswitchd/ovs-brcompatd.c
+++ b/vswitchd/ovs-brcompatd.c
@@ -43,6 +43,7 @@
 #include "leak-checker.h"
 #include "netdev.h"
 #include "netlink.h"
+#include "netlink-socket.h"
 #include "ofpbuf.h"
 #include "openvswitch/brcompat-netlink.h"
 #include "ovsdb-idl.h"
diff --git a/vswitchd/proc-net-compat.c b/vswitchd/proc-net-compat.c
index d8160f45f..e3b7ee489 100644
--- a/vswitchd/proc-net-compat.c
+++ b/vswitchd/proc-net-compat.c
@@ -25,6 +25,7 @@
 #include "dynamic-string.h"
 #include "hash.h"
 #include "netlink-protocol.h"
+#include "netlink-socket.h"
 #include "netlink.h"
 #include "ofpbuf.h"
 #include "openvswitch/brcompat-netlink.h"