Fork of Original Code Base: anongit.freedesktop.org/systemd

This is the initial fork of the code base from freedsktop.org.
The code is provided here as a reference of the initial starting
point and for possible future checkouts after a large portion
of this code is removed.

Merge git://anongit.freedesktop.org/systemd/systemd

1 files changed, 782 insertions, 0 deletions

diff --git a/src/libudev/libudev-monitor.c b/src/libudev/libudev-monitor.c
new file mode 100644
index 0000000000..b02ea8808c
--- /dev/null
+++ b/src/libudev/libudev-monitor.c
@@ -0,0 +1,782 @@
+/***
+  This file is part of systemd.
+
+  Copyright 2008-2012 Kay Sievers <kay@vrfy.org>
+
+  systemd 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; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stddef.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include <dirent.h>
+#include <sys/poll.h>
+#include <sys/stat.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <arpa/inet.h>
+#include <linux/netlink.h>
+#include <linux/filter.h>
+
+#include "libudev.h"
+#include "libudev-private.h"
+#include "socket-util.h"
+
+/**
+ * SECTION:libudev-monitor
+ * @short_description: device event source
+ *
+ * Connects to a device event source.
+ */
+
+/**
+ * udev_monitor:
+ *
+ * Opaque object handling an event source.
+ */
+struct udev_monitor {
+        struct udev *udev;
+        int refcount;
+        int sock;
+        union sockaddr_union snl;
+        union sockaddr_union snl_trusted_sender;
+        union sockaddr_union snl_destination;
+        socklen_t addrlen;
+        struct udev_list filter_subsystem_list;
+        struct udev_list filter_tag_list;
+        bool bound;
+};
+
+enum udev_monitor_netlink_group {
+        UDEV_MONITOR_NONE,
+        UDEV_MONITOR_KERNEL,
+        UDEV_MONITOR_UDEV,
+};
+
+#define UDEV_MONITOR_MAGIC                0xfeedcafe
+struct udev_monitor_netlink_header {
+        /* "libudev" prefix to distinguish libudev and kernel messages */
+        char prefix[8];
+        /*
+         * magic to protect against daemon <-> library message format mismatch
+         * used in the kernel from socket filter rules; needs to be stored in network order
+         */
+        unsigned int magic;
+        /* total length of header structure known to the sender */
+        unsigned int header_size;
+        /* properties string buffer */
+        unsigned int properties_off;
+        unsigned int properties_len;
+        /*
+         * hashes of primary device properties strings, to let libudev subscribers
+         * use in-kernel socket filters; values need to be stored in network order
+         */
+        unsigned int filter_subsystem_hash;
+        unsigned int filter_devtype_hash;
+        unsigned int filter_tag_bloom_hi;
+        unsigned int filter_tag_bloom_lo;
+};
+
+static struct udev_monitor *udev_monitor_new(struct udev *udev)
+{
+        struct udev_monitor *udev_monitor;
+
+        udev_monitor = calloc(1, sizeof(struct udev_monitor));
+        if (udev_monitor == NULL)
+                return NULL;
+        udev_monitor->refcount = 1;
+        udev_monitor->udev = udev;
+        udev_list_init(udev, &udev_monitor->filter_subsystem_list, false);
+        udev_list_init(udev, &udev_monitor->filter_tag_list, true);
+        return udev_monitor;
+}
+
+struct udev_monitor *udev_monitor_new_from_netlink_fd(struct udev *udev, const char *name, int fd)
+{
+        struct udev_monitor *udev_monitor;
+        unsigned int group;
+
+        if (udev == NULL)
+                return NULL;
+
+        if (name == NULL)
+                group = UDEV_MONITOR_NONE;
+        else if (strcmp(name, "udev") == 0)
+                group = UDEV_MONITOR_UDEV;
+        else if (strcmp(name, "kernel") == 0)
+                group = UDEV_MONITOR_KERNEL;
+        else
+                return NULL;
+
+        udev_monitor = udev_monitor_new(udev);
+        if (udev_monitor == NULL)
+                return NULL;
+
+        if (fd < 0) {
+                udev_monitor->sock = socket(PF_NETLINK, SOCK_RAW|SOCK_CLOEXEC|SOCK_NONBLOCK, NETLINK_KOBJECT_UEVENT);
+                if (udev_monitor->sock == -1) {
+                        udev_err(udev, "error getting socket: %m\n");
+                        free(udev_monitor);
+                        return NULL;
+                }
+        } else {
+                udev_monitor->bound = true;
+                udev_monitor->sock = fd;
+        }
+
+        udev_monitor->snl.nl.nl_family = AF_NETLINK;
+        udev_monitor->snl.nl.nl_groups = group;
+
+        /* default destination for sending */
+        udev_monitor->snl_destination.nl.nl_family = AF_NETLINK;
+        udev_monitor->snl_destination.nl.nl_groups = UDEV_MONITOR_UDEV;
+
+        return udev_monitor;
+}
+
+/**
+ * udev_monitor_new_from_netlink:
+ * @udev: udev library context
+ * @name: name of event source
+ *
+ * Create new udev monitor and connect to a specified event
+ * source. Valid sources identifiers are "udev" and "kernel".
+ *
+ * Applications should usually not connect directly to the
+ * "kernel" events, because the devices might not be useable
+ * at that time, before udev has configured them, and created
+ * device nodes. Accessing devices at the same time as udev,
+ * might result in unpredictable behavior. The "udev" events
+ * are sent out after udev has finished its event processing,
+ * all rules have been processed, and needed device nodes are
+ * created.
+ *
+ * The initial refcount is 1, and needs to be decremented to
+ * release the resources of the udev monitor.
+ *
+ * Returns: a new udev monitor, or #NULL, in case of an error
+ **/
+_public_ struct udev_monitor *udev_monitor_new_from_netlink(struct udev *udev, const char *name)
+{
+        return udev_monitor_new_from_netlink_fd(udev, name, -1);
+}
+
+static inline void bpf_stmt(struct sock_filter *inss, unsigned int *i,
+                            unsigned short code, unsigned int data)
+{
+        struct sock_filter *ins = &inss[*i];
+
+        ins->code = code;
+        ins->k = data;
+        (*i)++;
+}
+
+static inline void bpf_jmp(struct sock_filter *inss, unsigned int *i,
+                           unsigned short code, unsigned int data,
+                           unsigned short jt, unsigned short jf)
+{
+        struct sock_filter *ins = &inss[*i];
+
+        ins->code = code;
+        ins->jt = jt;
+        ins->jf = jf;
+        ins->k = data;
+        (*i)++;
+}
+
+/**
+ * udev_monitor_filter_update:
+ * @udev_monitor: monitor
+ *
+ * Update the installed socket filter. This is only needed,
+ * if the filter was removed or changed.
+ *
+ * Returns: 0 on success, otherwise a negative error value.
+ */
+_public_ int udev_monitor_filter_update(struct udev_monitor *udev_monitor)
+{
+        struct sock_filter ins[512];
+        struct sock_fprog filter;
+        unsigned int i;
+        struct udev_list_entry *list_entry;
+        int err;
+
+        if (udev_list_get_entry(&udev_monitor->filter_subsystem_list) == NULL &&
+            udev_list_get_entry(&udev_monitor->filter_tag_list) == NULL)
+                return 0;
+
+        memset(ins, 0x00, sizeof(ins));
+        i = 0;
+
+        /* load magic in A */
+        bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, magic));
+        /* jump if magic matches */
+        bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, UDEV_MONITOR_MAGIC, 1, 0);
+        /* wrong magic, pass packet */
+        bpf_stmt(ins, &i, BPF_RET|BPF_K, 0xffffffff);
+
+        if (udev_list_get_entry(&udev_monitor->filter_tag_list) != NULL) {
+                int tag_matches;
+
+                /* count tag matches, to calculate end of tag match block */
+                tag_matches = 0;
+                udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_tag_list))
+                        tag_matches++;
+
+                /* add all tags matches */
+                udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_tag_list)) {
+                        uint64_t tag_bloom_bits = util_string_bloom64(udev_list_entry_get_name(list_entry));
+                        uint32_t tag_bloom_hi = tag_bloom_bits >> 32;
+                        uint32_t tag_bloom_lo = tag_bloom_bits & 0xffffffff;
+
+                        /* load device bloom bits in A */
+                        bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, filter_tag_bloom_hi));
+                        /* clear bits (tag bits & bloom bits) */
+                        bpf_stmt(ins, &i, BPF_ALU|BPF_AND|BPF_K, tag_bloom_hi);
+                        /* jump to next tag if it does not match */
+                        bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, tag_bloom_hi, 0, 3);
+
+                        /* load device bloom bits in A */
+                        bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, filter_tag_bloom_lo));
+                        /* clear bits (tag bits & bloom bits) */
+                        bpf_stmt(ins, &i, BPF_ALU|BPF_AND|BPF_K, tag_bloom_lo);
+                        /* jump behind end of tag match block if tag matches */
+                        tag_matches--;
+                        bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, tag_bloom_lo, 1 + (tag_matches * 6), 0);
+                }
+
+                /* nothing matched, drop packet */
+                bpf_stmt(ins, &i, BPF_RET|BPF_K, 0);
+        }
+
+        /* add all subsystem matches */
+        if (udev_list_get_entry(&udev_monitor->filter_subsystem_list) != NULL) {
+                udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_subsystem_list)) {
+                        unsigned int hash = util_string_hash32(udev_list_entry_get_name(list_entry));
+
+                        /* load device subsystem value in A */
+                        bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, filter_subsystem_hash));
+                        if (udev_list_entry_get_value(list_entry) == NULL) {
+                                /* jump if subsystem does not match */
+                                bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, hash, 0, 1);
+                        } else {
+                                /* jump if subsystem does not match */
+                                bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, hash, 0, 3);
+
+                                /* load device devtype value in A */
+                                bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, filter_devtype_hash));
+                                /* jump if value does not match */
+                                hash = util_string_hash32(udev_list_entry_get_value(list_entry));
+                                bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, hash, 0, 1);
+                        }
+
+                        /* matched, pass packet */
+                        bpf_stmt(ins, &i, BPF_RET|BPF_K, 0xffffffff);
+
+                        if (i+1 >= ELEMENTSOF(ins))
+                                return -1;
+                }
+
+                /* nothing matched, drop packet */
+                bpf_stmt(ins, &i, BPF_RET|BPF_K, 0);
+        }
+
+        /* matched, pass packet */
+        bpf_stmt(ins, &i, BPF_RET|BPF_K, 0xffffffff);
+
+        /* install filter */
+        memset(&filter, 0x00, sizeof(filter));
+        filter.len = i;
+        filter.filter = ins;
+        err = setsockopt(udev_monitor->sock, SOL_SOCKET, SO_ATTACH_FILTER, &filter, sizeof(filter));
+        return err;
+}
+
+int udev_monitor_allow_unicast_sender(struct udev_monitor *udev_monitor, struct udev_monitor *sender)
+{
+        udev_monitor->snl_trusted_sender.nl.nl_pid = sender->snl.nl.nl_pid;
+        return 0;
+}
+/**
+ * udev_monitor_enable_receiving:
+ * @udev_monitor: the monitor which should receive events
+ *
+ * Binds the @udev_monitor socket to the event source.
+ *
+ * Returns: 0 on success, otherwise a negative error value.
+ */
+_public_ int udev_monitor_enable_receiving(struct udev_monitor *udev_monitor)
+{
+        int err = 0;
+        const int on = 1;
+
+        if (udev_monitor->snl.nl.nl_family == 0)
+                return -EINVAL;
+
+        udev_monitor_filter_update(udev_monitor);
+
+        if (!udev_monitor->bound) {
+                err = bind(udev_monitor->sock,
+                           &udev_monitor->snl.sa, sizeof(struct sockaddr_nl));
+                if (err == 0)
+                        udev_monitor->bound = true;
+        }
+
+        if (err >= 0) {
+                union sockaddr_union snl;
+                socklen_t addrlen;
+
+                /*
+                 * get the address the kernel has assigned us
+                 * it is usually, but not necessarily the pid
+                 */
+                addrlen = sizeof(struct sockaddr_nl);
+                err = getsockname(udev_monitor->sock, &snl.sa, &addrlen);
+                if (err == 0)
+                        udev_monitor->snl.nl.nl_pid = snl.nl.nl_pid;
+        } else {
+                udev_err(udev_monitor->udev, "bind failed: %m\n");
+                return err;
+        }
+
+        /* enable receiving of sender credentials */
+        setsockopt(udev_monitor->sock, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on));
+        return 0;
+}
+
+/**
+ * udev_monitor_set_receive_buffer_size:
+ * @udev_monitor: the monitor which should receive events
+ * @size: the size in bytes
+ *
+ * Set the size of the kernel socket buffer. This call needs the
+ * appropriate privileges to succeed.
+ *
+ * Returns: 0 on success, otherwise -1 on error.
+ */
+_public_ int udev_monitor_set_receive_buffer_size(struct udev_monitor *udev_monitor, int size)
+{
+        if (udev_monitor == NULL)
+                return -1;
+        return setsockopt(udev_monitor->sock, SOL_SOCKET, SO_RCVBUFFORCE, &size, sizeof(size));
+}
+
+int udev_monitor_disconnect(struct udev_monitor *udev_monitor)
+{
+        int err;
+
+        err = close(udev_monitor->sock);
+        udev_monitor->sock = -1;
+        return err;
+}
+
+/**
+ * udev_monitor_ref:
+ * @udev_monitor: udev monitor
+ *
+ * Take a reference of a udev monitor.
+ *
+ * Returns: the passed udev monitor
+ **/
+_public_ struct udev_monitor *udev_monitor_ref(struct udev_monitor *udev_monitor)
+{
+        if (udev_monitor == NULL)
+                return NULL;
+        udev_monitor->refcount++;
+        return udev_monitor;
+}
+
+/**
+ * udev_monitor_unref:
+ * @udev_monitor: udev monitor
+ *
+ * Drop a reference of a udev monitor. If the refcount reaches zero,
+ * the bound socket will be closed, and the resources of the monitor
+ * will be released.
+ *
+ * Returns: the passed udev monitor if it has still an active reference, or #NULL otherwise.
+ **/
+_public_ struct udev_monitor *udev_monitor_unref(struct udev_monitor *udev_monitor)
+{
+        if (udev_monitor == NULL)
+                return NULL;
+        udev_monitor->refcount--;
+        if (udev_monitor->refcount > 0)
+                return udev_monitor;
+        if (udev_monitor->sock >= 0)
+                close(udev_monitor->sock);
+        udev_list_cleanup(&udev_monitor->filter_subsystem_list);
+        udev_list_cleanup(&udev_monitor->filter_tag_list);
+        free(udev_monitor);
+        return NULL;
+}
+
+/**
+ * udev_monitor_get_udev:
+ * @udev_monitor: udev monitor
+ *
+ * Retrieve the udev library context the monitor was created with.
+ *
+ * Returns: the udev library context
+ **/
+_public_ struct udev *udev_monitor_get_udev(struct udev_monitor *udev_monitor)
+{
+        if (udev_monitor == NULL)
+                return NULL;
+        return udev_monitor->udev;
+}
+
+/**
+ * udev_monitor_get_fd:
+ * @udev_monitor: udev monitor
+ *
+ * Retrieve the socket file descriptor associated with the monitor.
+ *
+ * Returns: the socket file descriptor
+ **/
+_public_ int udev_monitor_get_fd(struct udev_monitor *udev_monitor)
+{
+        if (udev_monitor == NULL)
+                return -1;
+        return udev_monitor->sock;
+}
+
+static int passes_filter(struct udev_monitor *udev_monitor, struct udev_device *udev_device)
+{
+        struct udev_list_entry *list_entry;
+
+        if (udev_list_get_entry(&udev_monitor->filter_subsystem_list) == NULL)
+                goto tag;
+        udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_subsystem_list)) {
+                const char *subsys = udev_list_entry_get_name(list_entry);
+                const char *dsubsys = udev_device_get_subsystem(udev_device);
+                const char *devtype;
+                const char *ddevtype;
+
+                if (strcmp(dsubsys, subsys) != 0)
+                        continue;
+
+                devtype = udev_list_entry_get_value(list_entry);
+                if (devtype == NULL)
+                        goto tag;
+                ddevtype = udev_device_get_devtype(udev_device);
+                if (ddevtype == NULL)
+                        continue;
+                if (strcmp(ddevtype, devtype) == 0)
+                        goto tag;
+        }
+        return 0;
+
+tag:
+        if (udev_list_get_entry(&udev_monitor->filter_tag_list) == NULL)
+                return 1;
+        udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_tag_list)) {
+                const char *tag = udev_list_entry_get_name(list_entry);
+
+                if (udev_device_has_tag(udev_device, tag))
+                        return 1;
+        }
+        return 0;
+}
+
+/**
+ * udev_monitor_receive_device:
+ * @udev_monitor: udev monitor
+ *
+ * Receive data from the udev monitor socket, allocate a new udev
+ * device, fill in the received data, and return the device.
+ *
+ * Only socket connections with uid=0 are accepted.
+ *
+ * The monitor socket is by default set to NONBLOCK. A variant of poll() on
+ * the file descriptor returned by udev_monitor_get_fd() should to be used to
+ * wake up when new devices arrive, or alternatively the file descriptor
+ * switched into blocking mode.
+ *
+ * The initial refcount is 1, and needs to be decremented to
+ * release the resources of the udev device.
+ *
+ * Returns: a new udev device, or #NULL, in case of an error
+ **/
+_public_ struct udev_device *udev_monitor_receive_device(struct udev_monitor *udev_monitor)
+{
+        struct udev_device *udev_device;
+        struct msghdr smsg;
+        struct iovec iov;
+        char cred_msg[CMSG_SPACE(sizeof(struct ucred))];
+        struct cmsghdr *cmsg;
+        union sockaddr_union snl;
+        struct ucred *cred;
+        char buf[8192];
+        ssize_t buflen;
+        ssize_t bufpos;
+        struct udev_monitor_netlink_header *nlh;
+
+retry:
+        if (udev_monitor == NULL)
+                return NULL;
+        iov.iov_base = &buf;
+        iov.iov_len = sizeof(buf);
+        memset (&smsg, 0x00, sizeof(struct msghdr));
+        smsg.msg_iov = &iov;
+        smsg.msg_iovlen = 1;
+        smsg.msg_control = cred_msg;
+        smsg.msg_controllen = sizeof(cred_msg);
+
+        if (udev_monitor->snl.nl.nl_family != 0) {
+                smsg.msg_name = &snl;
+                smsg.msg_namelen = sizeof(snl);
+        }
+
+        buflen = recvmsg(udev_monitor->sock, &smsg, 0);
+        if (buflen < 0) {
+                if (errno != EINTR)
+                        udev_dbg(udev_monitor->udev, "unable to receive message\n");
+                return NULL;
+        }
+
+        if (buflen < 32 || (size_t)buflen >= sizeof(buf)) {
+                udev_dbg(udev_monitor->udev, "invalid message length\n");
+                return NULL;
+        }
+
+        if (udev_monitor->snl.nl.nl_family != 0) {
+                if (snl.nl.nl_groups == 0) {
+                        /* unicast message, check if we trust the sender */
+                        if (udev_monitor->snl_trusted_sender.nl.nl_pid == 0 ||
+                            snl.nl.nl_pid != udev_monitor->snl_trusted_sender.nl.nl_pid) {
+                                udev_dbg(udev_monitor->udev, "unicast netlink message ignored\n");
+                                return NULL;
+                        }
+                } else if (snl.nl.nl_groups == UDEV_MONITOR_KERNEL) {
+                        if (snl.nl.nl_pid > 0) {
+                                udev_dbg(udev_monitor->udev, "multicast kernel netlink message from pid %d ignored\n",
+                                     snl.nl.nl_pid);
+                                return NULL;
+                        }
+                }
+        }
+
+        cmsg = CMSG_FIRSTHDR(&smsg);
+        if (cmsg == NULL || cmsg->cmsg_type != SCM_CREDENTIALS) {
+                udev_dbg(udev_monitor->udev, "no sender credentials received, message ignored\n");
+                return NULL;
+        }
+
+        cred = (struct ucred *)CMSG_DATA(cmsg);
+        if (cred->uid != 0) {
+                udev_dbg(udev_monitor->udev, "sender uid=%d, message ignored\n", cred->uid);
+                return NULL;
+        }
+
+        if (memcmp(buf, "libudev", 8) == 0) {
+                /* udev message needs proper version magic */
+                nlh = (struct udev_monitor_netlink_header *) buf;
+                if (nlh->magic != htonl(UDEV_MONITOR_MAGIC)) {
+                        udev_err(udev_monitor->udev, "unrecognized message signature (%x != %x)\n",
+                            nlh->magic, htonl(UDEV_MONITOR_MAGIC));
+                        return NULL;
+                }
+                if (nlh->properties_off+32 > (size_t)buflen)
+                        return NULL;
+                bufpos = nlh->properties_off;
+        } else {
+                /* kernel message with header */
+                bufpos = strlen(buf) + 1;
+                if ((size_t)bufpos < sizeof("a@/d") || bufpos >= buflen) {
+                        udev_dbg(udev_monitor->udev, "invalid message length\n");
+                        return NULL;
+                }
+
+                /* check message header */
+                if (strstr(buf, "@/") == NULL) {
+                        udev_dbg(udev_monitor->udev, "unrecognized message header\n");
+                        return NULL;
+                }
+        }
+
+        udev_device = udev_device_new(udev_monitor->udev);
+        if (udev_device == NULL)
+                return NULL;
+        udev_device_set_info_loaded(udev_device);
+
+        while (bufpos < buflen) {
+                char *key;
+                size_t keylen;
+
+                key = &buf[bufpos];
+                keylen = strlen(key);
+                if (keylen == 0)
+                        break;
+                bufpos += keylen + 1;
+                udev_device_add_property_from_string_parse(udev_device, key);
+        }
+
+        if (udev_device_add_property_from_string_parse_finish(udev_device) < 0) {
+                udev_dbg(udev_monitor->udev, "missing values, invalid device\n");
+                udev_device_unref(udev_device);
+                return NULL;
+        }
+
+        /* skip device, if it does not pass the current filter */
+        if (!passes_filter(udev_monitor, udev_device)) {
+                struct pollfd pfd[1];
+                int rc;
+
+                udev_device_unref(udev_device);
+
+                /* if something is queued, get next device */
+                pfd[0].fd = udev_monitor->sock;
+                pfd[0].events = POLLIN;
+                rc = poll(pfd, 1, 0);
+                if (rc > 0)
+                        goto retry;
+                return NULL;
+        }
+
+        return udev_device;
+}
+
+int udev_monitor_send_device(struct udev_monitor *udev_monitor,
+                             struct udev_monitor *destination, struct udev_device *udev_device)
+{
+        const char *buf;
+        ssize_t blen;
+        ssize_t count;
+        struct msghdr smsg;
+        struct iovec iov[2];
+        const char *val;
+        struct udev_monitor_netlink_header nlh;
+        struct udev_list_entry *list_entry;
+        uint64_t tag_bloom_bits;
+
+        if (udev_monitor->snl.nl.nl_family == 0)
+                return -EINVAL;
+
+        blen = udev_device_get_properties_monitor_buf(udev_device, &buf);
+        if (blen < 32)
+                return -EINVAL;
+
+        /* add versioned header */
+        memset(&nlh, 0x00, sizeof(struct udev_monitor_netlink_header));
+        memcpy(nlh.prefix, "libudev", 8);
+        nlh.magic = htonl(UDEV_MONITOR_MAGIC);
+        nlh.header_size = sizeof(struct udev_monitor_netlink_header);
+        val = udev_device_get_subsystem(udev_device);
+        nlh.filter_subsystem_hash = htonl(util_string_hash32(val));
+        val = udev_device_get_devtype(udev_device);
+        if (val != NULL)
+                nlh.filter_devtype_hash = htonl(util_string_hash32(val));
+        iov[0].iov_base = &nlh;
+        iov[0].iov_len = sizeof(struct udev_monitor_netlink_header);
+
+        /* add tag bloom filter */
+        tag_bloom_bits = 0;
+        udev_list_entry_foreach(list_entry, udev_device_get_tags_list_entry(udev_device))
+                tag_bloom_bits |= util_string_bloom64(udev_list_entry_get_name(list_entry));
+        if (tag_bloom_bits > 0) {
+                nlh.filter_tag_bloom_hi = htonl(tag_bloom_bits >> 32);
+                nlh.filter_tag_bloom_lo = htonl(tag_bloom_bits & 0xffffffff);
+        }
+
+        /* add properties list */
+        nlh.properties_off = iov[0].iov_len;
+        nlh.properties_len = blen;
+        iov[1].iov_base = (char *)buf;
+        iov[1].iov_len = blen;
+
+        memset(&smsg, 0x00, sizeof(struct msghdr));
+        smsg.msg_iov = iov;
+        smsg.msg_iovlen = 2;
+        /*
+         * Use custom address for target, or the default one.
+         *
+         * If we send to a multicast group, we will get
+         * ECONNREFUSED, which is expected.
+         */
+        if (destination != NULL)
+                smsg.msg_name = &destination->snl;
+        else
+                smsg.msg_name = &udev_monitor->snl_destination;
+        smsg.msg_namelen = sizeof(struct sockaddr_nl);
+        count = sendmsg(udev_monitor->sock, &smsg, 0);
+        udev_dbg(udev_monitor->udev, "passed %zi bytes to netlink monitor %p\n", count, udev_monitor);
+        return count;
+}
+
+/**
+ * udev_monitor_filter_add_match_subsystem_devtype:
+ * @udev_monitor: the monitor
+ * @subsystem: the subsystem value to match the incoming devices against
+ * @devtype: the devtype value to match the incoming devices against
+ *
+ * This filter is efficiently executed inside the kernel, and libudev subscribers
+ * will usually not be woken up for devices which do not match.
+ *
+ * The filter must be installed before the monitor is switched to listening mode.
+ *
+ * Returns: 0 on success, otherwise a negative error value.
+ */
+_public_ int udev_monitor_filter_add_match_subsystem_devtype(struct udev_monitor *udev_monitor, const char *subsystem, const char *devtype)
+{
+        if (udev_monitor == NULL)
+                return -EINVAL;
+        if (subsystem == NULL)
+                return -EINVAL;
+        if (udev_list_entry_add(&udev_monitor->filter_subsystem_list, subsystem, devtype) == NULL)
+                return -ENOMEM;
+        return 0;
+}
+
+/**
+ * udev_monitor_filter_add_match_tag:
+ * @udev_monitor: the monitor
+ * @tag: the name of a tag
+ *
+ * This filter is efficiently executed inside the kernel, and libudev subscribers
+ * will usually not be woken up for devices which do not match.
+ *
+ * The filter must be installed before the monitor is switched to listening mode.
+ *
+ * Returns: 0 on success, otherwise a negative error value.
+ */
+_public_ int udev_monitor_filter_add_match_tag(struct udev_monitor *udev_monitor, const char *tag)
+{
+        if (udev_monitor == NULL)
+                return -EINVAL;
+        if (tag == NULL)
+                return -EINVAL;
+        if (udev_list_entry_add(&udev_monitor->filter_tag_list, tag, NULL) == NULL)
+                return -ENOMEM;
+        return 0;
+}
+
+/**
+ * udev_monitor_filter_remove:
+ * @udev_monitor: monitor
+ *
+ * Remove all filters from monitor.
+ *
+ * Returns: 0 on success, otherwise a negative error value.
+ */
+_public_ int udev_monitor_filter_remove(struct udev_monitor *udev_monitor)
+{
+        static struct sock_fprog filter = { 0, NULL };
+
+        udev_list_cleanup(&udev_monitor->filter_subsystem_list);
+        return setsockopt(udev_monitor->sock, SOL_SOCKET, SO_ATTACH_FILTER, &filter, sizeof(filter));
+}