nl.c

/*
 * lib/nl.c             Core Netlink Interface
 *
 *      This library is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU Lesser General Public
 *      License as published by the Free Software Foundation version 2.1
 *      of the License.
 *
 * Copyright (c) 2003-2012 Thomas Graf <tgraf@suug.ch>
 */

/**
 * @defgroup core Core Library (libnl)
 *
 * Socket handling, connection management, sending and receiving of data,
 * message construction and parsing, object caching system, ...
 *
 * This is the API reference of the core library. It is not meant as a guide
 * but as a reference. Please refer to the core library guide for detailed
 * documentation on the library architecture and examples:
 *
 * * @ref_asciidoc{core,_,Netlink Core Library Development Guide}
 *
 *
 * @{
 */

#include <netlink-private/netlink.h>
#include <netlink/netlink.h>
#include <netlink/utils.h>
#include <netlink/handlers.h>
#include <netlink/msg.h>
#include <netlink/attr.h>

/**
 * @defgroup core_types Data Types
 *
 * Core library data types
 * @{
 * @}
 *
 * @defgroup send_recv Send & Receive Data
 *
 * Connection management, sending & receiving of data
 *
 * Related sections in the development guide:
 * - @core_doc{core_send_recv, Sending & Receiving}
 * - @core_doc{core_sockets, Sockets}
 *
 * @{
 *
 * Header
 * ------
 * ~~~~{.c}
 * #include <netlink/netlink.h>
 * ~~~~
 */

/**
 * @name Connection Management
 * @{
 */

/**
 * Create file descriptor and bind socket.
 * @arg sk              Netlink socket (required)
 * @arg protocol        Netlink protocol to use (required)
 *
 * Creates a new Netlink socket using `socket()` and binds the socket to the
 * protocol and local port specified in the `sk` socket object. Fails if
 * the socket is already connected.
 *
 * @note If available, the `close-on-exec` (`SOCK_CLOEXEC`) feature is enabled
 *       automatically on the new file descriptor. This causes the socket to
 *       be closed automatically if any of the `exec` family functions succeed.
 *       This is essential for multi threaded programs.
 *
 * @see nl_socket_alloc()
 * @see nl_close()
 *
 * @return 0 on success or a negative error code.
 *
 * @retval -NLE_BAD_SOCK Socket is already connected
 */
int nl_connect(struct nl_sock *sk, int protocol)
{
        int err, flags = 0;
        socklen_t addrlen;

#ifdef SOCK_CLOEXEC
        flags |= SOCK_CLOEXEC;
#endif

        if (sk->s_fd != -1)
                return -NLE_BAD_SOCK;

        sk->s_fd = socket(AF_NETLINK, SOCK_RAW | flags, protocol);
        if (sk->s_fd < 0) {
                err = -nl_syserr2nlerr(errno);
                goto errout;
        }

        if (!(sk->s_flags & NL_SOCK_BUFSIZE_SET)) {
                err = nl_socket_set_buffer_size(sk, 0, 0);
                if (err < 0)
                        goto errout;
        }

        err = bind(sk->s_fd, (struct sockaddr*) &sk->s_local,
                   sizeof(sk->s_local));
        if (err < 0) {
                err = -nl_syserr2nlerr(errno);
                goto errout;
        }

        addrlen = sizeof(sk->s_local);
        err = getsockname(sk->s_fd, (struct sockaddr *) &sk->s_local,
                          &addrlen);
        if (err < 0) {
                err = -nl_syserr2nlerr(errno);
                goto errout;
        }

        if (addrlen != sizeof(sk->s_local)) {
                err = -NLE_NOADDR;
                goto errout;
        }

        if (sk->s_local.nl_family != AF_NETLINK) {
                err = -NLE_AF_NOSUPPORT;
                goto errout;
        }

        sk->s_proto = protocol;

        return 0;
errout:
        if (sk->s_fd != -1) {
                close(sk->s_fd);
                sk->s_fd = -1;
        }

        return err;
}

/**
 * Close Netlink socket
 * @arg sk              Netlink socket (required)
 *
 * Closes the Netlink socket using `close()`.
 *
 * @note The socket is closed automatically if a `struct nl_sock` object is
 *       freed using `nl_socket_free()`.
 *
 * @see nl_connect()
 */
void nl_close(struct nl_sock *sk)
{
        if (sk->s_fd >= 0) {
                close(sk->s_fd);
                sk->s_fd = -1;
        }

        sk->s_proto = 0;
}

/** @} */

/**
 * @name Send
 * @{
 */

/**
 * Transmit raw data over Netlink socket.
 * @arg sk              Netlink socket (required)
 * @arg buf             Buffer carrying data to send (required)
 * @arg size            Size of buffer (required)
 *
 * Transmits "raw" data over the specified Netlink socket. Unlike the other
 * transmit functions it does not modify the data in any way. It directly
 * passes the buffer \c buf of \c size to sendto().
 *
 * The message is addressed to the peer as specified in the socket by either
 * the nl_socket_set_peer_port() or nl_socket_set_peer_groups() function.
 *
 * @note Because there is no indication on the message boundaries of the data
 *       being sent, the \c NL_CB_MSG_OUT callback handler will not be invoked
 *       for data that is being sent using this function.
 *
 * @see nl_socket_set_peer_port()
 * @see nl_socket_set_peer_groups()
 * @see nl_sendmsg()
 *
 * @return Number of bytes sent or a negative error code.
 */
int nl_sendto(struct nl_sock *sk, void *buf, size_t size)
{
        int ret;

        if (!buf)
                return -NLE_INVAL;

        if (sk->s_fd < 0)
                return -NLE_BAD_SOCK;

        ret = sendto(sk->s_fd, buf, size, 0, (struct sockaddr *)
                     &sk->s_peer, sizeof(sk->s_peer));
        if (ret < 0)
                return -nl_syserr2nlerr(errno);

        return ret;
}

/**
 * Transmit Netlink message using sendmsg()
 * @arg sk              Netlink socket (required)
 * @arg msg             Netlink message to be sent (required)
 * @arg hdr             sendmsg() message header (required)
 *
 * Transmits the message specified in \c hdr over the Netlink socket using the
 * sendmsg() system call.
 *
 * @attention
 * The `msg` argument will *not* be used to derive the message payload that
 * is being sent out. The `msg` argument is *only* passed on to the
 * `NL_CB_MSG_OUT` callback. The caller is responsible to initialize the
 * `hdr` struct properly and have it point to the message payload and
 * socket address.
 *
 * @note
 * This function uses `nlmsg_set_src()` to modify the `msg` argument prior to
 * invoking the `NL_CB_MSG_OUT` callback to provide the local port number.
 *
 * @callback This function triggers the `NL_CB_MSG_OUT` callback.
 *
 * @attention
 * Think twice before using this function. It provides a low level access to
 * the Netlink socket. Among other limitations, it does not add credentials
 * even if enabled or respect the destination address specified in the `msg`
 * object.
 *
 * @see nl_socket_set_local_port()
 * @see nl_send_auto()
 * @see nl_send_iovec()
 *
 * @return Number of bytes sent on success or a negative error code.
 *
 * @lowlevel
 */
int nl_sendmsg(struct nl_sock *sk, struct nl_msg *msg, struct msghdr *hdr)
{
        struct nl_cb *cb;
        int ret;

        if (sk->s_fd < 0)
                return -NLE_BAD_SOCK;

        nlmsg_set_src(msg, &sk->s_local);

        cb = sk->s_cb;
        if (cb->cb_set[NL_CB_MSG_OUT])
                if ((ret = nl_cb_call(cb, NL_CB_MSG_OUT, msg)) != NL_OK)
                        return ret;

        ret = sendmsg(sk->s_fd, hdr, 0);
        if (ret < 0)
                return -nl_syserr2nlerr(errno);

        NL_DBG(4, "sent %d bytes\n", ret);
        return ret;
}


/**
 * Transmit Netlink message (taking IO vector)
 * @arg sk              Netlink socket (required)
 * @arg msg             Netlink message to be sent (required)
 * @arg iov             IO vector to be sent (required)
 * @arg iovlen          Number of struct iovec to be sent (required)
 *
 * This function is identical to nl_send() except that instead of taking a
 * `struct nl_msg` object it takes an IO vector. Please see the description
 * of `nl_send()`.
 *
 * @callback This function triggers the `NL_CB_MSG_OUT` callback.
 *
 * @see nl_send()
 *
 * @return Number of bytes sent on success or a negative error code.
 *
 * @lowlevel
 */
int nl_send_iovec(struct nl_sock *sk, struct nl_msg *msg, struct iovec *iov, unsigned iovlen)
{
        struct sockaddr_nl *dst;
        struct ucred *creds;
        struct msghdr hdr = {
                .msg_name = (void *) &sk->s_peer,
                .msg_namelen = sizeof(struct sockaddr_nl),
                .msg_iov = iov,
                .msg_iovlen = iovlen,
        };

        /* Overwrite destination if specified in the message itself, defaults
         * to the peer address of the socket.
         */
        dst = nlmsg_get_dst(msg);
        if (dst->nl_family == AF_NETLINK)
                hdr.msg_name = dst;

        /* Add credentials if present. */
        creds = nlmsg_get_creds(msg);
        if (creds != NULL) {
                char buf[CMSG_SPACE(sizeof(struct ucred))];
                struct cmsghdr *cmsg;

                hdr.msg_control = buf;
                hdr.msg_controllen = sizeof(buf);

                cmsg = CMSG_FIRSTHDR(&hdr);
                cmsg->cmsg_level = SOL_SOCKET;
                cmsg->cmsg_type = SCM_CREDENTIALS;
                cmsg->cmsg_len = CMSG_LEN(sizeof(struct ucred));
                memcpy(CMSG_DATA(cmsg), creds, sizeof(struct ucred));
        }

        return nl_sendmsg(sk, msg, &hdr);
}

/**
 * Transmit Netlink message
 * @arg sk              Netlink socket (required)
 * @arg msg             Netlink message (required)
 *
 * Transmits the Netlink message `msg` over the Netlink socket using the
 * `sendmsg()` system call. This function is based on `nl_send_iovec()` but
 * takes care of initializing a `struct iovec` based on the `msg` object.
 *
 * The message is addressed to the peer as specified in the socket by either
 * the nl_socket_set_peer_port() or nl_socket_set_peer_groups() function.
 * The peer address can be overwritten by specifying an address in the `msg`
 * object using nlmsg_set_dst().
 *
 * If present in the `msg`, credentials set by the nlmsg_set_creds() function
 * are added to the control buffer of the message.
 *
 * @par Overwriting Capability:
 * Calls to this function can be overwritten by providing an alternative using
 * the nl_cb_overwrite_send() function.
 *
 * @callback This function triggers the `NL_CB_MSG_OUT` callback.
 *
 * @attention
 * Unlike `nl_send_auto()`, this function does *not* finalize the message in
 * terms of automatically adding needed flags or filling out port numbers.
 *
 * @see nl_send_auto()
 * @see nl_send_iovec()
 * @see nl_socket_set_peer_port()
 * @see nl_socket_set_peer_groups()
 * @see nlmsg_set_dst()
 * @see nlmsg_set_creds()
 * @see nl_cb_overwrite_send()
 *
 * @return Number of bytes sent on success or a negative error code.
*/
int nl_send(struct nl_sock *sk, struct nl_msg *msg)
{
        struct nl_cb *cb = sk->s_cb;

        if (cb->cb_send_ow)
                return cb->cb_send_ow(sk, msg);
        else {
                struct iovec iov = {
                        .iov_base = (void *) nlmsg_hdr(msg),
                        .iov_len = nlmsg_hdr(msg)->nlmsg_len,
                };

                return nl_send_iovec(sk, msg, &iov, 1);
        }
}

/**
 * Finalize Netlink message
 * @arg sk              Netlink socket (required)
 * @arg msg             Netlink message (required)
 *
 * This function finalizes a Netlink message by completing the message with
 * desirable flags and values depending on the socket configuration.
 *
 *  - If not yet filled out, the source address of the message (`nlmsg_pid`)
 *    will be set to the local port number of the socket.
 *  - If not yet specified, the next available sequence number is assigned
 *    to the message (`nlmsg_seq`).
 *  - If not yet specified, the protocol field of the message will be set to
 *    the protocol field of the socket.
 *  - The `NLM_F_REQUEST` Netlink message flag will be set.
 *  - The `NLM_F_ACK` flag will be set if Auto-ACK mode is enabled on the
 *    socket.
 */
void nl_complete_msg(struct nl_sock *sk, struct nl_msg *msg)
{
        struct nlmsghdr *nlh;

        nlh = nlmsg_hdr(msg);
        if (nlh->nlmsg_pid == NL_AUTO_PORT)
                nlh->nlmsg_pid = sk->s_local.nl_pid;

        if (nlh->nlmsg_seq == NL_AUTO_SEQ)
                nlh->nlmsg_seq = sk->s_seq_next++;

        if (msg->nm_protocol == -1)
                msg->nm_protocol = sk->s_proto;

        nlh->nlmsg_flags |= NLM_F_REQUEST;

        if (!(sk->s_flags & NL_NO_AUTO_ACK))
                nlh->nlmsg_flags |= NLM_F_ACK;
}

/**
 * Finalize and transmit Netlink message
 * @arg sk              Netlink socket (required)
 * @arg msg             Netlink message (required)
 *
 * Finalizes the message by passing it to `nl_complete_msg()` and transmits it
 * by passing it to `nl_send()`.
 *
 * @callback This function triggers the `NL_CB_MSG_OUT` callback.
 *
 * @see nl_complete_msg()
 * @see nl_send()
 *
 * @return Number of bytes sent or a negative error code.
 */
int nl_send_auto(struct nl_sock *sk, struct nl_msg *msg)
{
        nl_complete_msg(sk, msg);

        return nl_send(sk, msg);
}

/**
 * Finalize and transmit Netlink message and wait for ACK or error message
 * @arg sk              Netlink socket (required)
 * @arg msg             Netlink message (required)
 *
 * Passes the `msg` to `nl_send_auto()` to finalize and transmit it. Frees the
 * message and waits (sleeps) for the ACK or error message to be received.
 *
 * @attention
 * Disabling Auto-ACK (nl_socket_disable_auto_ack()) will cause this function
 * to return immediately after transmitting the message. However, the peer may
 * still be returning an error message in response to the request. It is the
 * responsibility of the caller to handle such messages.
 *
 * @callback This function triggers the `NL_CB_MSG_OUT` callback.
 *
 * @attention
 * This function frees the `msg` object after transmitting it by calling
 * `nlmsg_free()`.
 *
 * @see nl_send_auto().
 * @see nl_wait_for_ack()
 *
 * @return 0 on success or a negative error code.
 */
int nl_send_sync(struct nl_sock *sk, struct nl_msg *msg)
{
        int err;

        err = nl_send_auto(sk, msg);
        nlmsg_free(msg);
        if (err < 0)
                return err;

        return wait_for_ack(sk);
}

/**
 * Construct and transmit a Netlink message
 * @arg sk              Netlink socket (required)
 * @arg type            Netlink message type (required)
 * @arg flags           Netlink message flags (optional)
 * @arg buf             Data buffer (optional)
 * @arg size            Size of data buffer (optional)
 *
 * Allocates a new Netlink message based on `type` and `flags`. If `buf`
 * points to payload of length `size` that payload will be appended to the
 * message.
 *
 * Sends out the message using `nl_send_auto()` and frees the message
 * afterwards.
 *
 * @see nl_send_auto()
 *
 * @return Number of characters sent on success or a negative error code.
 * @retval -NLE_NOMEM Unable to allocate Netlink message
 */
int nl_send_simple(struct nl_sock *sk, int type, int flags, void *buf,
                   size_t size)
{
        int err;
        struct nl_msg *msg;

        msg = nlmsg_alloc_simple(type, flags);
        if (!msg)
                return -NLE_NOMEM;

        if (buf && size) {
                err = nlmsg_append(msg, buf, size, NLMSG_ALIGNTO);
                if (err < 0)
                        goto errout;
        }

        err = nl_send_auto(sk, msg);
errout:
        nlmsg_free(msg);

        return err;
}

/** @} */

/**
 * @name Receive
 * @{
 */

/**
 * Receive data from netlink socket
 * @arg sk              Netlink socket (required)
 * @arg nla             Netlink socket structure to hold address of peer (required)
 * @arg buf             Destination pointer for message content (required)
 * @arg creds           Destination pointer for credentials (optional)
 *
 * Receives data from a connected netlink socket using recvmsg() and returns
 * the number of bytes read. The read data is stored in a newly allocated
 * buffer that is assigned to \c *buf. The peer's netlink address will be
 * stored in \c *nla.
 *
 * This function blocks until data is available to be read unless the socket
 * has been put into non-blocking mode using nl_socket_set_nonblocking() in
 * which case this function will return immediately with a return value of 0.
 *
 * The buffer size used when reading from the netlink socket and thus limiting
 * the maximum size of a netlink message that can be read defaults to the size
 * of a memory page (getpagesize()). The buffer size can be modified on a per
 * socket level using the function nl_socket_set_msg_buf_size().
 *
 * If message peeking is enabled using nl_socket_enable_msg_peek() the size of
 * the message to be read will be determined using the MSG_PEEK flag prior to
 * performing the actual read. This leads to an additional recvmsg() call for
 * every read operation which has performance implications and is not
 * recommended for high throughput protocols.
 *
 * An eventual interruption of the recvmsg() system call is automatically
 * handled by retrying the operation.
 *
 * If receiving of credentials has been enabled using the function
 * nl_socket_set_passcred(), this function will allocate a new struct ucred
 * filled with the received credentials and assign it to \c *creds. The caller
 * is responsible for freeing the buffer.
 *
 * @note The caller is responsible to free the returned data buffer and if
 *       enabled, the credentials buffer.
 *
 * @see nl_socket_set_nonblocking()
 * @see nl_socket_set_msg_buf_size()
 * @see nl_socket_enable_msg_peek()
 * @see nl_socket_set_passcred()
 *
 * @return Number of bytes read, 0 on EOF, 0 on no data event (non-blocking
 *         mode), or a negative error code.
 */
int nl_recv(struct nl_sock *sk, struct sockaddr_nl *nla,
            unsigned char **buf, struct ucred **creds)
{
        ssize_t n;
        int flags = 0;
        static int page_size = 0;
        struct iovec iov;
        struct msghdr msg = {
                .msg_name = (void *) nla,
                .msg_namelen = sizeof(struct sockaddr_nl),
                .msg_iov = &iov,
                .msg_iovlen = 1,
        };
        struct ucred* tmpcreds = NULL;
        int retval = 0;

        if (!buf || !nla)
                return -NLE_INVAL;

        if (sk->s_flags & NL_MSG_PEEK)
                flags |= MSG_PEEK | MSG_TRUNC;

        if (page_size == 0)
                page_size = getpagesize() * 4;

        iov.iov_len = sk->s_bufsize ? : page_size;
        iov.iov_base = malloc(iov.iov_len);

        if (!iov.iov_base) {
                retval = -NLE_NOMEM;
                goto abort;
        }

        if (creds && (sk->s_flags & NL_SOCK_PASSCRED)) {
                msg.msg_controllen = CMSG_SPACE(sizeof(struct ucred));
                msg.msg_control = malloc(msg.msg_controllen);
                if (!msg.msg_control) {
                        retval = -NLE_NOMEM;
                        goto abort;
                }
        }
retry:

        n = recvmsg(sk->s_fd, &msg, flags);
        if (!n) {
                retval = 0;
                goto abort;
        }
        if (n < 0) {
                if (errno == EINTR) {
                        NL_DBG(3, "recvmsg() returned EINTR, retrying\n");
                        goto retry;
                }
                retval = -nl_syserr2nlerr(errno);
                goto abort;
        }

        if (msg.msg_flags & MSG_CTRUNC) {
                void *tmp;
                msg.msg_controllen *= 2;
                tmp = realloc(msg.msg_control, msg.msg_controllen);
                if (!tmp) {
                        retval = -NLE_NOMEM;
                        goto abort;
                }
                msg.msg_control = tmp;
                goto retry;
        }

        if (iov.iov_len < n || (msg.msg_flags & MSG_TRUNC)) {
                void *tmp;
                /* Provided buffer is not long enough, enlarge it
                 * to size of n (which should be total length of the message)
                 * and try again. */
                iov.iov_len = n;
                tmp = realloc(iov.iov_base, iov.iov_len);
                if (!tmp) {
                        retval = -NLE_NOMEM;
                        goto abort;
                }
                iov.iov_base = tmp;
                flags = 0;
                goto retry;
        }

        if (flags != 0) {
                /* Buffer is big enough, do the actual reading */
                flags = 0;
                goto retry;
        }

        if (msg.msg_namelen != sizeof(struct sockaddr_nl)) {
                retval =  -NLE_NOADDR;
                goto abort;
        }

        if (creds && (sk->s_flags & NL_SOCK_PASSCRED)) {
                struct cmsghdr *cmsg;

                for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
                        if (cmsg->cmsg_level != SOL_SOCKET)
                                continue;
                        if (cmsg->cmsg_type != SCM_CREDENTIALS)
                                continue;
                        tmpcreds = malloc(sizeof(*tmpcreds));
                        if (!tmpcreds) {
                                retval = -NLE_NOMEM;
                                goto abort;
                        }
                        memcpy(tmpcreds, CMSG_DATA(cmsg), sizeof(*tmpcreds));
                        break;
                }
        }

        retval = n;
abort:
        free(msg.msg_control);

        if (retval <= 0) {
                free(iov.iov_base);
                iov.iov_base = NULL;
                free(tmpcreds);
                tmpcreds = NULL;
        } else
                *buf = iov.iov_base;

        if (creds)
                *creds = tmpcreds;

        return retval;
}

/** @cond SKIP */
#define NL_CB_CALL(cb, type, msg) \
do { \
        err = nl_cb_call(cb, type, msg); \
        switch (err) { \
        case NL_OK: \
                err = 0; \
                break; \
        case NL_SKIP: \
                goto skip; \
        case NL_STOP: \
                goto stop; \
        default: \
                goto out; \
        } \
} while (0)
/** @endcond */

static int recvmsgs(struct nl_sock *sk, struct nl_cb *cb)
{
        int n, err = 0, multipart = 0, interrupted = 0, nrecv = 0;
        unsigned char *buf = NULL;
        struct nlmsghdr *hdr;

        /*
        nla is passed on to not only to nl_recv() but may also be passed
        to a function pointer provided by the caller which may or may not
        initialize the variable. Thomas Graf.
        */
        struct sockaddr_nl nla = {0};
        struct nl_msg *msg = NULL;
        struct ucred *creds = NULL;

continue_reading:
        NL_DBG(3, "Attempting to read from %p\n", sk);
        if (cb->cb_recv_ow)
                n = cb->cb_recv_ow(sk, &nla, &buf, &creds);
        else
                n = nl_recv(sk, &nla, &buf, &creds);

        if (n <= 0)
                return n;

        NL_DBG(3, "recvmsgs(%p): Read %d bytes\n", sk, n);

        hdr = (struct nlmsghdr *) buf;
        while (nlmsg_ok(hdr, n)) {
                NL_DBG(3, "recvmsgs(%p): Processing valid message...\n", sk);

                nlmsg_free(msg);
                msg = nlmsg_convert(hdr);
                if (!msg) {
                        err = -NLE_NOMEM;
                        goto out;
                }

                nlmsg_set_proto(msg, sk->s_proto);
                nlmsg_set_src(msg, &nla);
                if (creds)
                        nlmsg_set_creds(msg, creds);

                nrecv++;

                /* Raw callback is the first, it gives the most control
                 * to the user and he can do his very own parsing. */
                if (cb->cb_set[NL_CB_MSG_IN])
                        NL_CB_CALL(cb, NL_CB_MSG_IN, msg);

                /* Sequence number checking. The check may be done by
                 * the user, otherwise a very simple check is applied
                 * enforcing strict ordering */
                if (cb->cb_set[NL_CB_SEQ_CHECK]) {
                        NL_CB_CALL(cb, NL_CB_SEQ_CHECK, msg);

                /* Only do sequence checking if auto-ack mode is enabled */
                } else if (!(sk->s_flags & NL_NO_AUTO_ACK)) {
                        if (hdr->nlmsg_seq != sk->s_seq_expect) {
                                if (cb->cb_set[NL_CB_INVALID])
                                        NL_CB_CALL(cb, NL_CB_INVALID, msg);
                                else {
                                        err = -NLE_SEQ_MISMATCH;
                                        goto out;
                                }
                        }
                }

                if (hdr->nlmsg_type == NLMSG_DONE ||
                    hdr->nlmsg_type == NLMSG_ERROR ||
                    hdr->nlmsg_type == NLMSG_NOOP ||
                    hdr->nlmsg_type == NLMSG_OVERRUN) {
                        /* We can't check for !NLM_F_MULTI since some netlink
                         * users in the kernel are broken. */
                        sk->s_seq_expect++;
                        NL_DBG(3, "recvmsgs(%p): Increased expected " \
                               "sequence number to %d\n",
                               sk, sk->s_seq_expect);
                }

                if (hdr->nlmsg_flags & NLM_F_MULTI)
                        multipart = 1;

                if (hdr->nlmsg_flags & NLM_F_DUMP_INTR) {
                        if (cb->cb_set[NL_CB_DUMP_INTR])
                                NL_CB_CALL(cb, NL_CB_DUMP_INTR, msg);
                        else {
                                /*
                                 * We have to continue reading to clear
                                 * all messages until a NLMSG_DONE is
                                 * received and report the inconsistency.
                                 */
                                interrupted = 1;
                        }
                }
        
                /* Other side wishes to see an ack for this message */
                if (hdr->nlmsg_flags & NLM_F_ACK) {
                        if (cb->cb_set[NL_CB_SEND_ACK])
                                NL_CB_CALL(cb, NL_CB_SEND_ACK, msg);
                        else {
                                /* FIXME: implement */
                        }
                }

                /* messages terminates a multipart message, this is
                 * usually the end of a message and therefore we slip
                 * out of the loop by default. the user may overrule
                 * this action by skipping this packet. */
                if (hdr->nlmsg_type == NLMSG_DONE) {
                        multipart = 0;
                        if (cb->cb_set[NL_CB_FINISH])
                                NL_CB_CALL(cb, NL_CB_FINISH, msg);
                }

                /* Message to be ignored, the default action is to
                 * skip this message if no callback is specified. The
                 * user may overrule this action by returning
                 * NL_PROCEED. */
                else if (hdr->nlmsg_type == NLMSG_NOOP) {
                        if (cb->cb_set[NL_CB_SKIPPED])
                                NL_CB_CALL(cb, NL_CB_SKIPPED, msg);
                        else
                                goto skip;
                }

                /* Data got lost, report back to user. The default action is to
                 * quit parsing. The user may overrule this action by retuning
                 * NL_SKIP or NL_PROCEED (dangerous) */
                else if (hdr->nlmsg_type == NLMSG_OVERRUN) {
                        if (cb->cb_set[NL_CB_OVERRUN])
                                NL_CB_CALL(cb, NL_CB_OVERRUN, msg);
                        else {
                                err = -NLE_MSG_OVERFLOW;
                                goto out;
                        }
                }

                /* Message carries a nlmsgerr */
                else if (hdr->nlmsg_type == NLMSG_ERROR) {
                        struct nlmsgerr *e = nlmsg_data(hdr);

                        if (hdr->nlmsg_len < nlmsg_size(sizeof(*e))) {
                                /* Truncated error message, the default action
                                 * is to stop parsing. The user may overrule
                                 * this action by returning NL_SKIP or
                                 * NL_PROCEED (dangerous) */
                                if (cb->cb_set[NL_CB_INVALID])
                                        NL_CB_CALL(cb, NL_CB_INVALID, msg);
                                else {
                                        err = -NLE_MSG_TRUNC;
                                        goto out;
                                }
                        } else if (e->error) {
                                /* Error message reported back from kernel. */
                                if (cb->cb_err) {
                                        err = cb->cb_err(&nla, e,
                                                           cb->cb_err_arg);
                                        if (err < 0)
                                                goto out;
                                        else if (err == NL_SKIP)
                                                goto skip;
                                        else if (err == NL_STOP) {
                                                err = -nl_syserr2nlerr(e->error);
                                                goto out;
                                        }
                                } else {
                                        err = -nl_syserr2nlerr(e->error);
                                        goto out;
                                }
                        } else if (cb->cb_set[NL_CB_ACK])
                                NL_CB_CALL(cb, NL_CB_ACK, msg);
                } else {
                        /* Valid message (not checking for MULTIPART bit to
                         * get along with broken kernels. NL_SKIP has no
                         * effect on this.  */
                        if (cb->cb_set[NL_CB_VALID])
                                NL_CB_CALL(cb, NL_CB_VALID, msg);
                }
skip:
                err = 0;
                hdr = nlmsg_next(hdr, &n);
        }
        
        nlmsg_free(msg);
        free(buf);
        free(creds);
        buf = NULL;
        msg = NULL;
        creds = NULL;

        if (multipart) {
                /* Multipart message not yet complete, continue reading */
                goto continue_reading;
        }
stop:
        err = 0;
out:
        nlmsg_free(msg);
        free(buf);
        free(creds);

        if (interrupted)
                err = -NLE_DUMP_INTR;

        if (!err)
                err = nrecv;

        return err;
}

/**
 * Receive a set of messages from a netlink socket and report parsed messages
 * @arg sk              Netlink socket.
 * @arg cb              set of callbacks to control behaviour.
 *
 * This function is identical to nl_recvmsgs() to the point that it will
 * return the number of parsed messages instead of 0 on success.
 *
 * @see nl_recvmsgs()
 *
 * @return Number of received messages or a negative error code from nl_recv().
 */
int nl_recvmsgs_report(struct nl_sock *sk, struct nl_cb *cb)
{
        if (cb->cb_recvmsgs_ow)
                return cb->cb_recvmsgs_ow(sk, cb);
        else
                return recvmsgs(sk, cb);
}

/**
 * Receive a set of messages from a netlink socket.
 * @arg sk              Netlink socket.
 * @arg cb              set of callbacks to control behaviour.
 *
 * Repeatedly calls nl_recv() or the respective replacement if provided
 * by the application (see nl_cb_overwrite_recv()) and parses the
 * received data as netlink messages. Stops reading if one of the
 * callbacks returns NL_STOP or nl_recv returns either 0 or a negative error code.
 *
 * A non-blocking sockets causes the function to return immediately if
 * no data is available.
 *
 * @see nl_recvmsgs_report()
 *
 * @return 0 on success or a negative error code from nl_recv().
 */
int nl_recvmsgs(struct nl_sock *sk, struct nl_cb *cb)
{
        int err;

        if ((err = nl_recvmsgs_report(sk, cb)) > 0)
                err = 0;

        return err;
}

/**
 * Receive a set of message from a netlink socket using handlers in nl_sock.
 * @arg sk              Netlink socket.
 *
 * Calls nl_recvmsgs() with the handlers configured in the netlink socket.
 */
int nl_recvmsgs_default(struct nl_sock *sk)
{
        return nl_recvmsgs(sk, sk->s_cb);

}

static int ack_wait_handler(struct nl_msg *msg, void *arg)
{
        return NL_STOP;
}

/**
 * Wait for ACK.
 * @arg sk              Netlink socket.
 * @pre The netlink socket must be in blocking state.
 *
 * Waits until an ACK is received for the latest not yet acknowledged
 * netlink message.
 */
int nl_wait_for_ack(struct nl_sock *sk)
{
        int err;
        struct nl_cb *cb;

        cb = nl_cb_clone(sk->s_cb);
        if (cb == NULL)
                return -NLE_NOMEM;

        nl_cb_set(cb, NL_CB_ACK, NL_CB_CUSTOM, ack_wait_handler, NULL);
        err = nl_recvmsgs(sk, cb);
        nl_cb_put(cb);

        return err;
}

/** @cond SKIP */
struct pickup_param
{
        int (*parser)(struct nl_cache_ops *, struct sockaddr_nl *,
                      struct nlmsghdr *, struct nl_parser_param *);
        struct nl_object *result;
};

static int __store_answer(struct nl_object *obj, struct nl_parser_param *p)
{
        struct pickup_param *pp = p->pp_arg;
        /*
         * the parser will put() the object at the end, expecting the cache
         * to take the reference.
         */
        nl_object_get(obj);
        pp->result =  obj;

        return 0;
}

static int __pickup_answer(struct nl_msg *msg, void *arg)
{
        struct pickup_param *pp = arg;
        struct nl_parser_param parse_arg = {
                .pp_cb = __store_answer,
                .pp_arg = pp,
        };

        return pp->parser(NULL, &msg->nm_src, msg->nm_nlh, &parse_arg);
}

/** @endcond */

/**
 * Pickup netlink answer, parse is and return object
 * @arg sk              Netlink socket
 * @arg parser          Parser function to parse answer
 * @arg result          Result pointer to return parsed object
 *
 * @return 0 on success or a negative error code.
 */
int nl_pickup(struct nl_sock *sk,
              int (*parser)(struct nl_cache_ops *, struct sockaddr_nl *,
                            struct nlmsghdr *, struct nl_parser_param *),
              struct nl_object **result)
{
        struct nl_cb *cb;
        int err;
        struct pickup_param pp = {
                .parser = parser,
        };

        cb = nl_cb_clone(sk->s_cb);
        if (cb == NULL)
                return -NLE_NOMEM;

        nl_cb_set(cb, NL_CB_VALID, NL_CB_CUSTOM, __pickup_answer, &pp);

        err = nl_recvmsgs(sk, cb);
        if (err < 0)
                goto errout;

        *result = pp.result;
errout:
        nl_cb_put(cb);

        return err;
}

/** @} */

/**
 * @name Deprecated
 * @{
 */

/**
 * @deprecated Please use nl_complete_msg()
 */
void nl_auto_complete(struct nl_sock *sk, struct nl_msg *msg)
{
        nl_complete_msg(sk, msg);
}

/**
 * @deprecated Please use nl_send_auto()
 */
int nl_send_auto_complete(struct nl_sock *sk, struct nl_msg *msg)
{
        return nl_send_auto(sk, msg);
}


/** @} */

/** @} */

/** @} */