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Diffstat (limited to 'man7/netlink.7')
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diff --git a/man7/netlink.7 b/man7/netlink.7 index 58835fe8d6..fcc5470dfd 100644 --- a/man7/netlink.7 +++ b/man7/netlink.7 @@ -1,460 +1,8 @@ -'\" t -.\" Don't change the first line, it tells man that tbl is needed. -.\" This man page is Copyright (c) 1998 by Andi Kleen. Subject to the GPL. -.\" Based on the original comments from Alexey Kuznetsov -.\" Modified 2005-12-27 by Hasso Tepper <hasso@estpak.ee> -.\" $Id: netlink.7,v 1.8 2000/06/22 13:23:00 ak Exp $ -.TH NETLINK 7 2005-12-27 "Linux" "Linux Programmer's Manual" -.SH NAME -netlink \- Communication between kernel and userspace (PF_NETLINK) -.SH SYNOPSIS -.nf -.B #include <asm/types.h> -.B #include <sys/socket.h> -.B #include <linux/netlink.h> - -.BI "netlink_socket = socket(PF_NETLINK, " socket_type ", " netlink_family ); -.fi -.SH DESCRIPTION -Netlink is used to transfer information between kernel and -userspace processes. -It consists of a standard sockets-based interface for userspace -processes and an internal kernel API for kernel modules. -The internal kernel interface is not documented in this manual page. -There is also an obsolete netlink interface -via netlink character devices; this interface is not documented here -and is only provided for backwards compatibility. - -Netlink is a datagram-oriented service. -Both -.B SOCK_RAW -and -.B SOCK_DGRAM -are valid values for -.IR socket_type . -However, the netlink protocol does not distinguish between datagram -and raw sockets. - -.I netlink_family -selects the kernel module or netlink group to communicate with. -The currently assigned netlink families are: -.TP -.B NETLINK_ROUTE -Receives routing and link updates and may be used to modify the routing -tables (both IPv4 and IPv6), IP addresses, link parameters, -neighbor setups, queueing disciplines, traffic classes and -packet classifiers (see -.BR rtnetlink (7)). -.TP -.B NETLINK_W1 -Messages from 1-wire subsystem. -.TP -.B NETLINK_USERSOCK -Reserved for user-mode socket protocols. -.TP -.B NETLINK_FIREWALL -Transport IPv4 packets from netfilter to userspace. -Used by -.I ip_queue -kernel module. -.TP -.B NETLINK_INET_DIAG -.\" FIXME More details on NETLINK_INET_DIAG needed. -INET socket monitoring. -.TP -.B NETLINK_NFLOG -Netfilter/iptables ULOG. -.TP -.B NETLINK_XFRM -.\" FIXME More details on NETLINK_XFRM needed. -IPsec. -.TP -.B NETLINK_SELINUX -SELinux event notifications. -.TP -.B NETLINK_ISCSI -.\" FIXME More details on NETLINK_ISCSI needed. -Open-iSCSI. -.TP -.B NETLINK_AUDIT -.\" FIXME More details on NETLINK_AUDIT needed. -Auditing. -.TP -.B NETLINK_FIB_LOOKUP -.\" FIXME More details on NETLINK_FIB_LOOKUP needed. -Access to FIB lookup from userspace. -.TP -.B NETLINK_CONNECTOR -Kernel connector. -See -.I Documentation/connector/* -in the kernel source for further information. -.TP -.B NETLINK_NETFILTER -.\" FIXME More details on NETLINK_NETFILTER needed. -Netfilter subsystem. -.TP -.B NETLINK_IP6_FW -Transport IPv6 packets from netfilter to userspace. -Used by -.I ip6_queue -kernel module. -.TP -.B NETLINK_DNRTMSG -DECnet routing messages. -.TP -.B NETLINK_KOBJECT_UEVENT -.\" FIXME More details on NETLINK_KOBJECT_UEVENT needed. -Kernel messages to userspace. -.TP -.B NETLINK_GENERIC -Generic netlink family for simplified netlink usage. -.PP -Netlink messages consist of a byte stream with one or multiple -.I nlmsghdr -headers and associated payload. -The byte stream should only be accessed with the standard -.B NLMSG_* -macros. -See -.BR netlink (3) -for further information. - -In multipart messages (multiple -.I nlmsghdr -headers with associated payload in one byte stream) the first and all -following headers have the -.B NLM_F_MULTI -flag set, except for the last header which has the type -.BR NLMSG_DONE . - -After each -.I nlmsghdr -the payload follows. - -.in +4n -.nf -struct nlmsghdr { - __u32 nlmsg_len; /* Length of message including header. */ - __u16 nlmsg_type; /* Type of message content. */ - __u16 nlmsg_flags; /* Additional flags. */ - __u32 nlmsg_seq; /* Sequence number. */ - __u32 nlmsg_pid; /* PID of the sending process. */ -}; -.fi -.in - -.I nlmsg_type -can be one of the standard message types: -.B NLMSG_NOOP -message is to be ignored, -.B NLMSG_ERROR -message signals an error and the payload contains an -.I nlmsgerr -structure, -.B NLMSG_DONE -message terminates a multipart message. - -.in +4n -.nf -struct nlmsgerr { - int error; /* Negative errno or 0 for acknowledgements */ - struct nlmsghdr msg; /* Message header that caused the error */ -}; -.fi -.in - -A netlink family usually specifies more message types, see the -appropriate manual pages for that, for example, -.BR rtnetlink (7) -for -.BR NETLINK_ROUTE . - -Standard flag bits in -.I nlmsg_flags -.br ---------------------------------- -.TS -tab(:); -lB l. -NLM_F_REQUEST:Must be set on all request messages. -NLM_F_MULTI:T{ -The message is part of a multipart message terminated by -.BR NLMSG_DONE . -T} -NLM_F_ACK:Request for an acknowledgment on success. -NLM_F_ECHO:Echo this request. -.TE - -Additional flag bits for GET requests -.br -------------------------------------- -.TS -tab(:); -lB l. -NLM_F_ROOT:Return the complete table instead of a single entry. -NLM_F_MATCH:T{ -Return all entries matching criteria passed in message content. -Not implemented yet. -T} -.\" FIXME NLM_F_ATOMIC is not used any more? -NLM_F_ATOMIC:Return an atomic snapshot of the table. -NLM_F_DUMP:Convenience macro; equivalent to (NLM_F_ROOT|NLM_F_MATCH). -.TE - -Note that -.B NLM_F_ATOMIC -requires the -.B CAP_NET_ADMIN -capability or an effective UID of 0. - -Additional flag bits for NEW requests -.br -------------------------------------- -.TS -tab(:); -lB l. -NLM_F_REPLACE:Replace existing matching object. -NLM_F_EXCL:Don't replace if the object already exists. -NLM_F_CREATE:Create object if it doesn't already exist. -NLM_F_APPEND:Add to the end of the object list. -.TE - -.I nlmsg_seq -and -.I nlmsg_pid -are used to track messages. -.I nlmsg_pid -shows the origin of the message. -Note that there isn't a 1:1 relationship between -.I nlmsg_pid -and the PID of the process if the message originated from a netlink -socket. -See the -.B ADDRESS FORMATS -section for further information. - -Both -.I nlmsg_seq -and -.I nlmsg_pid -.\" FIXME Explain more about nlmsg_seq and nlmsg_pid. -are opaque to netlink core. - -Netlink is not a reliable protocol. -It tries its best to deliver a message to its destination(s), -but may drop messages when an out-of-memory condition or -other error occurs. -For reliable transfer the sender can request an -acknowledgement from the receiver by setting the -.B NLM_F_ACK -flag. -An acknowledgment is an -.B NLMSG_ERROR -packet with the error field set to 0. -The application must generate acknowledgements for -received messages itself. -The kernel tries to send an -.B NLMSG_ERROR -message for every failed packet. -A user process should follow this convention too. - -However, reliable transmissions from kernel to user are impossible -in any case. -The kernel can't send a netlink message if the socket buffer is full: -the message will be dropped and the kernel and the userspace process will -no longer have the same view of kernel state. -It is up to the application to detect when this happens (via the -.B ENOBUFS -error returned by -.BR recvmsg (2)) -and resynchronize. -.SS Address Formats -The -.I sockaddr_nl -structure describes a netlink client in user space or in the kernel. -A -.I sockaddr_nl -can be either unicast (only sent to one peer) or sent to -netlink multicast groups -.RI ( nl_groups -not equal 0). - -.in +4n -.nf -struct sockaddr_nl { - sa_family_t nl_family; /* AF_NETLINK */ - unsigned short nl_pad; /* Zero. */ - pid_t nl_pid; /* Process ID. */ - __u32 nl_groups; /* Multicast groups mask. */ -}; -.fi -.in - -.I nl_pid -is the unicast address of netlink socket. -It's always 0 if the destination is in the kernel. -For a userspace process, -.I nl_pid -is usually the PID of the process owning the destination socket. -However, -.I nl_pid -identifies a netlink socket, not a process. -If a process owns several netlink -sockets, then -.I nl_pid -can only be equal to the process ID for at most one socket. -There are two ways to assign -.I nl_pid -to a netlink socket. -If the application sets -.I nl_pid -before calling -.BR bind (2), -then it is up to the application to make sure that -.I nl_pid -is unique. -If the application sets it to 0, the kernel takes care of assigning it. -The kernel assigns the process ID to the first netlink socket the process -opens and assigns a unique -.I nl_pid -to every netlink socket that the process subsequently creates. - -.I nl_groups -is a bit mask with every bit representing a netlink group number. -Each netlink family has a set of 32 multicast groups. -When -.BR bind (2) -is called on the socket, the -.I nl_groups -field in the -.I sockaddr_nl -should be set to a bit mask of the groups which it wishes to listen to. -The default value for this field is zero which means that no multicasts -will be received. -A socket may multicast messages to any of the multicast groups by setting -.I nl_groups -to a bit mask of the groups it wishes to send to when it calls -.BR sendmsg (2) -or does a -.BR connect (2). -Only processes with an effective UID of 0 or the -.B CAP_NET_ADMIN -capability may send or listen to a netlink multicast group. -Any replies to a message received for a multicast group should be -sent back to the sending PID and the multicast group. -.SH VERSIONS -The socket interface to netlink is a new feature of Linux 2.2. - -Linux 2.0 supported a more primitive device based netlink interface -(which is still available as a compatibility option). -This obsolete interface is not described here. - -NETLINK_SELINUX appeared in Linux 2.6.4. - -NETLINK_AUDIT appeared in Linux 2.6.6. - -NETLINK_KOBJECT_UEVENT appeared in Linux 2.6.10. - -NETLINK_W1 and NETLINK_FIB_LOOKUP appeared in Linux 2.6.13. - -NETLINK_INET_DIAG, NETLINK_CONNECTOR and NETLINK_NETFILTER appeared in -Linux 2.6.14. - -NETLINK_GENERIC and NETLINK_ISCSI appeared in Linux 2.6.15. -.SH NOTES -It is often better to use netlink via -.I libnetlink -or -.I libnl -than via the low-level kernel interface. -.SH BUGS -This manual page is not complete. -.SH EXAMPLE -The following example creates a -.B NETLINK_ROUTE -netlink socket which will listen to the -.B RTMGRP_LINK -(network interface create/delete/up/down events) and -.B RTMGRP_IPV4_IFADDR -(IPv4 addresses add/delete events) multicast groups. - -.in +4n -.nf -struct sockaddr_nl sa; - -memset(&sa, 0, sizeof(sa)); -snl.nl_family = AF_NETLINK; -snl.nl_groups = RTMGRP_LINK | RTMGRP_IPV4_IFADDR; - -fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE); -bind(fd, (struct sockaddr*)&sa, sizeof(sa)); -.fi -.in - -The next example demonstrates how to send a netlink message to the -kernel (pid 0). -Note that application must take care of message sequence numbers -in order to reliably track acknowledgements. - -.in +4n -.nf -struct nlmsghdr *nh; /* The nlmsghdr with payload to send. */ -struct sockaddr_nl sa; -struct iovec iov = { (void *) nh, nh\->nlmsg_len }; -struct msghdr msg; - -msg = { (void *)&sa, sizeof(sa), &iov, 1, NULL, 0, 0 }; -memset(&sa, 0, sizeof(sa)); -sa.nl_family = AF_NETLINK; -nh\->nlmsg_pid = 0; -nh\->nlmsg_seq = ++sequence_number; -/* Request an ack from kernel by setting NLM_F_ACK. */ -nh\->nlmsg_flags |= NLM_F_ACK; - -sendmsg(fd, &msg, 0); -.fi -.in - -And the last example is about reading netlink message. - -.in +4n -.nf -int len; -char buf[4096]; -struct iovec iov = { buf, sizeof(buf) }; -struct sockaddr_nl sa; -struct msghdr msg; -struct nlmsghdr *nh; - -msg = { (void *)&sa, sizeof(sa), &iov, 1, NULL, 0, 0 }; -len = recvmsg(fd, &msg, 0); - -for (nh = (struct nlmsghdr *) buf; NLMSG_OK (nh, len); - nh = NLMSG_NEXT (nh, len)) { - /* The end of multipart message. */ - if (nh\->nlmsg_type == NLMSG_DONE) - return; - - if (nh\->nlmsg_type == NLMSG_ERROR) - /* Do some error handling. */ - ... - - /* Continue with parsing payload. */ - ... -} -.fi -.in -.SH "SEE ALSO" -.BR cmsg (3), -.BR netlink (3), -.BR capabilities (7), -.BR rtnetlink (7) -.PP -ftp://ftp.inr.ac.ru/ip-routing/iproute2* -for information about libnetlink. - -http://people.suug.ch/~tgr/libnl/ -for information about libnl. - -RFC 3549 "Linux Netlink as an IP Services Protocol" +.TH NETLINK 7 2008-08-07 "Linux" "Linux Programmer's Manual" +.TH NETLINK 7 2008-08-07 "Linux" "Linux Programmer's Manual" +.TH NETLINK 7 2008-08-07 "Linux" "Linux Programmer's Manual" +.TH NETLINK 7 2008-08-07 "Linux" "Linux Programmer's Manual" +.TH NETLINK 7 2008-08-07 "Linux" "Linux Programmer's Manual" +.TH NETLINK 7 2008-08-07 "Linux" "Linux Programmer's Manual" +.TH NETLINK 7 2008-08-07 "Linux" "Linux Programmer's Manual" +.TH NETLINK 7 2008-08-07 "Linux" "Linux Programmer's Manual" |