Re: [PATCH v2 1/3] sock_diag.7: New page documenting NETLINK_SOCK_DIAG interface

["Michael Kerrisk (man-pages)" <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 12/07/2016 02:59 PM, Dmitry V. Levin wrote:
> From: Pavel Emelyanov <xemul-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org>
> 
> Co-authored-by: Dmitry V. Levin <ldv-u2l5PoMzF/Vg9hUCZPvPmw@public.gmane.org>
> Signed-off-by: Pavel Emelyanov <xemul-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org>
> Signed-off-by: Dmitry V. Levin <ldv-u2l5PoMzF/Vg9hUCZPvPmw@public.gmane.org>

Thank you, Pavel and Dmitry, for all the work that went into this page!
I've applied and pushed to Git. I made a lot of trivial edits
to the page. You may want to review it, but I don't think
I broke anything. Perhaps the most notable change was to consistently
replace "protocol family" by "address family".

Cheers,

Michael


> ---
>  man7/sock_diag.7 | 865 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 865 insertions(+)
>  create mode 100644 man7/sock_diag.7
> 
> diff --git a/man7/sock_diag.7 b/man7/sock_diag.7
> new file mode 100644
> index 0000000..c4948d7
> --- /dev/null
> +++ b/man7/sock_diag.7
> @@ -0,0 +1,865 @@
> +.\" Copyright (c) 2016 Pavel Emelyanov <xemul-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org>
> +.\" Copyright (c) 2016 Dmitry V. Levin <ldv-u2l5PoMzF/Vg9hUCZPvPmw@public.gmane.org>
> +.\"
> +.\" %%%LICENSE_START(GPLv2+_DOC_FULL)
> +.\" This is free documentation; you can redistribute it and/or
> +.\" modify it under the terms of the GNU General Public License as
> +.\" published by the Free Software Foundation; either version 2 of
> +.\" the License, or (at your option) any later version.
> +.\"
> +.\" The GNU General Public License's references to "object code"
> +.\" and "executables" are to be interpreted as the output of any
> +.\" document formatting or typesetting system, including
> +.\" intermediate and printed output.
> +.\"
> +.\" This manual 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 General Public License for more details.
> +.\"
> +.\" You should have received a copy of the GNU General Public
> +.\" License along with this manual; if not, see
> +.\" <http://www.gnu.org/licenses/>.
> +.\" %%%LICENSE_END
> +.TH SOCK_DIAG 7 2016-12-07 "Linux" "Linux Programmer's Manual"
> +.SH NAME
> +sock_diag \- obtaining information about sockets
> +.SH SYNOPSIS
> +.nf
> +.B #include <sys/socket.h>
> +.B #include <linux/sock_diag.h>
> +.BR "#include <linux/unix_diag.h>" " /* for UNIX domain sockets */"
> +.BR "#include <linux/inet_diag.h>" " /* for IPv4 and IPv6 sockets */"
> +
> +.BI "diag_socket = socket(AF_NETLINK, " socket_type ", NETLINK_SOCK_DIAG);"
> +.fi
> +.SH DESCRIPTION
> +The sock_diag netlink subsystem provides a mechanism for obtaining
> +information about sockets of various protocol families from the kernel.
> +This subsystem can be used to obtain information about individual
> +sockets or request a list of sockets.
> +
> +In the request the caller can specify an additional information it would
> +like to obtain about the socket, e.g. memory information or
> +family-specific stuff.
> +
> +When requesting a list of sockets, the caller can specify filters that
> +would be applied by the kernel to select a subset of sockets to report.
> +For now there is only an ability to filter sockets by state (connected,
> +listening, etc.)
> +
> +Note that sock_diag reports only those sockets that have a name,
> +i.e. either bound explicitly with
> +.BR bind (2)
> +or sockets that were automatically bound to an address (e.g., by
> +.BR connect (2)).
> +This is the same set of sockets that is available via
> +.IR /proc/net/unix ,
> +.IR /proc/net/tcp ,
> +.IR /proc/net/udp ,
> +etc.
> +
> +.SS Request
> +The request starts with
> +.I "struct nlmsghdr"
> +header described in
> +.BR netlink (7)
> +with
> +.I nlmsg_type
> +field set to
> +.BR SOCK_DIAG_BY_FAMILY .
> +It is followed by a protocol family specific header that starts with
> +a common part shared by all protocol families:
> +
> +.in +4n
> +.nf
> +struct sock_diag_req {
> +    __u8 sdiag_family;
> +    __u8 sdiag_protocol;
> +};
> +.fi
> +.in
> +.PP
> +The fields of this structure are as follows:
> +.TP
> +.I sdiag_family
> +A protocol family.  It should be set to the appropriate
> +.B AF_*
> +constant.
> +.TP
> +.I sdiag_protocol
> +Depends on
> +.IR sdiag_family .
> +It should be set to the appropriate
> +.B IPPROTO_*
> +constant for
> +.B AF_INET
> +and
> +.BR AF_INET6,
> +and to 0 otherwise.
> +.PP
> +If
> +.I nlmsg_flags
> +field of the
> +.I "struct nlmsghdr"
> +header has
> +.BR NLM_F_DUMP
> +flag set, it means that a list of sockets is being requested,
> +otherwise it is a query about an individual socket.
> +
> +.SS Response
> +The response starts with
> +.I "struct nlmsghdr"
> +header and is followed by an array of family-specific objects.
> +The array is to be accessed with the standard
> +.B NLMSG_*
> +macros from
> +.BR netlink (3)
> +API.
> +.PP
> +Each object is the NLA (netlink attributes) list that is to be accessed
> +with the
> +.B RTA_*
> +macros from
> +.BR rtnetlink (3)
> +API.
> +
> +.SS UNIX domain sockets
> +For UNIX domain sockets the request is represented in the following structure:
> +
> +.in +4n
> +.nf
> +struct unix_diag_req {
> +    __u8    sdiag_family;
> +    __u8    sdiag_protocol;
> +    __u16   pad;
> +    __u32   udiag_states;
> +    __u32   udiag_ino;
> +    __u32   udiag_show;
> +    __u32   udiag_cookie[2];
> +};
> +.fi
> +.in
> +.PP
> +The fields of this structure are as follows:
> +.TP
> +.I sdiag_family
> +The protocol family, it should be set to
> +.BR AF_UNIX .
> +.PP
> +.I sdiag_protocol
> +.PD 0
> +.TP
> +.PD
> +.I pad
> +These fields should be set to 0.
> +.TP
> +.I udiag_states
> +This is a bit mask that defines a filter of sockets states.
> +Only those sockets whose states are in this mask will be reported.
> +Ignored when querying for an individual socket.
> +Supported values are:
> +.PD 0
> +.RS
> +.IP "" 2
> +1 <<
> +.B TCP_ESTABLISHED
> +.IP
> +1 <<
> +.B TCP_LISTEN
> +.RE
> +.PD
> +.TP
> +.I udiag_ino
> +This is an inode number when querying for an individual socket.
> +Ignored when querying for a list of sockets.
> +.TP
> +.I udiag_show
> +This is a set of flags defining what kind of information to report.
> +Each requested kind of information is reported back as a netlink
> +attribute as described below:
> +.RS
> +.IP "" 2
> +.B UDIAG_SHOW_NAME
> +.RS 4
> +The attribute reported in answer to this request is
> +.BR UNIX_DIAG_NAME .
> +The payload associated with this attribute is the pathname to which
> +the socket was bound (a sequence of bytes up to
> +.B UNIX_PATH_MAX
> +length).
> +.RE
> +.IP "" 2
> +.B UDIAG_SHOW_VFS
> +.RS 4
> +The attribute reported in answer to this request is
> +.BR UNIX_DIAG_VFS .
> +The payload associated with this attribute is represented in the following
> +structure:
> +
> +.in +4n
> +.nf
> +struct unix_diag_vfs {
> +    __u32 udiag_vfs_dev;
> +    __u32 udiag_vfs_ino;
> +};
> +.fi
> +.in
> +
> +The fields of this structure are as follows:
> +.PD 0
> +.RS 2
> +.IP "" 2
> +.I udiag_vfs_dev
> +The device number of the corresponding on-disk socket inode.
> +.IP
> +.I udiag_vfs_ino
> +The inode number of the corresponding on-disk socket inode.
> +.RE
> +.PD
> +.RE
> +.IP
> +.B UDIAG_SHOW_PEER
> +.RS 4
> +The attribute reported in answer to this request is
> +.BR UNIX_DIAG_PEER .
> +The payload associated with this attribute is a __u32 value
> +which is the peer's inode number.
> +This attribute is reported for connected sockets only.
> +.RE
> +.IP
> +.B UDIAG_SHOW_ICONS
> +.RS 4
> +The attribute reported in answer to this request is
> +.BR UNIX_DIAG_ICONS .
> +The payload associated with this attribute is an array of __u32 values
> +which are inode numbers of sockets that has passed the
> +.BR connect (2)
> +call, but hasn't been processed with
> +.BR accept (2)
> +yet.  This attribute is reported for listening sockets only.
> +.RE
> +.IP
> +.B UDIAG_SHOW_RQLEN
> +.RS 4
> +The attribute reported in answer to this request is
> +.BR UNIX_DIAG_RQLEN .
> +The payload associated with this attribute is represented in the following
> +structure:
> +
> +.in +4n
> +.nf
> +struct unix_diag_rqlen {
> +    __u32 udiag_rqueue;
> +    __u32 udiag_wqueue;
> +};
> +.fi
> +.in
> +
> +The fields of this structure are as follows:
> +.PD 0
> +.RS 2
> +.IP "" 2
> +.I udiag_rqueue
> +.RS 6
> +.IP "listening sockets:" 2
> +The number of pending connections.  The length of the array associated with
> +.B UNIX_DIAG_ICONS
> +response attribute is equal to this value.
> +.IP "established sockets:"
> +The amount of data in incoming queue.
> +.RE
> +.IP
> +.I udiag_wqueue
> +.RS 6
> +.IP "listening sockets:" 2
> +The backlog length which equals to the value passed as the second argument to
> +.BR listen (2).
> +.IP "established sockets:"
> +The amount of memory available for sending.
> +.RE
> +.RE
> +.PD
> +.RE
> +.IP
> +.B UDIAG_SHOW_MEMINFO
> +.RS 4
> +The attribute reported in answer to this request is
> +.BR UNIX_DIAG_MEMINFO .
> +The payload associated with this attribute is an array of __u32 values
> +described below in "Socket memory information" subsection.
> +.RE
> +.IP
> +.RE
> +.RS
> +The following attributes are reported back without any specific request:
> +.IP "" 2
> +.BR UNIX_DIAG_SHUTDOWN .
> +The payload associated with this attribute is __u8 value which represents
> +bits of
> +.BR shutdown (2)
> +state.
> +.RE
> +.TP
> +.I udiag_cookie
> +This is an array of opaque identifiers that could be used along with
> +.I udiag_ino
> +to specify an individual socket.  It is ignored when querying for a list
> +of sockets, as well as when all its elements are set to \-1.
> +.PP
> +The response to a query for UNIX domain sockets is represented as an array of
> +
> +.in +4n
> +.nf
> +struct unix_diag_msg {
> +    __u8    udiag_family;
> +    __u8    udiag_type;
> +    __u8    udiag_state;
> +    __u8    pad;
> +    __u32   udiag_ino;
> +    __u32   udiag_cookie[2];
> +};
> +.fi
> +.in
> +
> +followed by netlink attributes.
> +.PP
> +The fields of this structure are as follows:
> +.TP
> +.I udiag_family
> +This field has the same meaning as in
> +.IR "struct unix_diag_req" .
> +.TP
> +.I udiag_type
> +This is set to one of the following constants:
> +.PD 0
> +.RS
> +.IP "" 2
> +.B SOCK_PACKET
> +.IP
> +.B SOCK_STREAM
> +.IP
> +.B SOCK_SEQPACKET
> +.RE
> +.PD
> +.TP
> +.I udiag_state
> +This is set to one of the following constants:
> +.PD 0
> +.RS
> +.IP "" 2
> +.B TCP_LISTEN
> +.IP
> +.B TCP_ESTABLISHED
> +.RE
> +.PD
> +.TP
> +.I pad
> +This field is set to 0.
> +.TP
> +.I udiag_ino
> +This is the socket inode number.
> +.TP
> +.I udiag_cookie
> +This is an array of opaque identifiers that could be used in subsequent
> +queries.
> +
> +.SS IPv4 and IPv6 sockets
> +For IPv4 and IPv6 sockets the request is represented in the following structure:
> +
> +.in +4n
> +.nf
> +struct inet_diag_req_v2 {
> +    __u8    sdiag_family;
> +    __u8    sdiag_protocol;
> +    __u8    idiag_ext;
> +    __u8    pad;
> +    __u32   idiag_states;
> +    struct inet_diag_sockid id;
> +};
> +.fi
> +.in
> +
> +where
> +.I "struct inet_diag_sockid"
> +is defined as follows:
> +
> +.in +4n
> +.nf
> +struct inet_diag_sockid {
> +    __be16  idiag_sport;
> +    __be16  idiag_dport;
> +    __be32  idiag_src[4];
> +    __be32  idiag_dst[4];
> +    __u32   idiag_if;
> +    __u32   idiag_cookie[2];
> +};
> +.fi
> +.in
> +.PP
> +The fields of
> +.I "struct inet_diag_req_v2"
> +are as follows:
> +.TP
> +.I sdiag_family
> +This should be set to either
> +.B AF_INET
> +or
> +.B AF_INET6
> +for
> +.B IPv4
> +or
> +.B IPv6
> +sockets respectively.
> +.TP
> +.I sdiag_protocol
> +This should be set to one of the following constants:
> +.PD 0
> +.RS
> +.IP "" 2
> +.B IPPROTO_TCP
> +.IP
> +.B IPPROTO_UDP
> +.IP
> +.B IPPROTO_UDPLITE
> +.RE
> +.PD
> +.TP
> +.I idiag_ext
> +This is a set of flags defining what kind of extended information to report.
> +Each requested kind of information is reported back as a netlink attribute
> +as described below:
> +.RS
> +.TP
> +.B INET_DIAG_TOS
> +The payload associated with this attribute is a __u8 value
> +which is the TOS of the socket.
> +.TP
> +.B INET_DIAG_TCLASS
> +The payload associated with this attribute is a __u8 value
> +which is the TClass of the socket.  IPv6 sockets only.
> +For LISTEN and CLOSE sockets this is followed by
> +.B INET_DIAG_SKV6ONLY
> +attribute with associated __u8 payload value meaning whether the socket
> +is IPv6-only or not.
> +.TP
> +.B INET_DIAG_MEMINFO
> +The payload associated with this attribute is represented in the following
> +structure:
> +
> +.in +4n
> +.nf
> +struct inet_diag_meminfo {
> +    __u32 idiag_rmem;
> +    __u32 idiag_wmem;
> +    __u32 idiag_fmem;
> +    __u32 idiag_tmem;
> +};
> +.fi
> +.in
> +
> +The fields of this structure are as follows:
> +.RS
> +.TP 12
> +.I idiag_rmem
> +The amount of data in the receive queue.
> +.TP
> +.I idiag_wmem
> +The amount of data that is queued by TCP but not yet sent.
> +.TP
> +.I idiag_fmem
> +The amount of memory scheduled for future use (TCP only).
> +.TP
> +.I idiag_tmem
> +The amount of data in send queue.
> +.RE
> +.TP
> +.B INET_DIAG_SKMEMINFO
> +The payload associated with this attribute is an array of __u32 values
> +described below in "Socket memory information" subsection.
> +.TP
> +.B INET_DIAG_INFO
> +The payload associated with this attribute is protocol specific.
> +For TCP sockets it is an object of type
> +.IR "struct tcp_info" .
> +.TP
> +.B INET_DIAG_CONG
> +The payload associated with this attribute is a string that describes the
> +congestion control algorithm used.  For TCP sockets only.
> +.RE
> +.TP
> +.I pad
> +This should be set to 0.
> +.TP
> +.I idiag_states
> +This is a bit mask that defines a filter of sockets states.
> +Only those sockets whose states are in this mask will be reported.
> +Ignored when querying for an individual socket.
> +.TP
> +.I id
> +This is a socket id object that is used in dump requests, in queries
> +about individual sockets, and is reported back in each response.
> +Unlike UNIX domain sockets, IPv4 and IPv6 sockets are identified
> +using addresses and ports.  All values are in network byte order.
> +.PP
> +The fields of
> +.I "struct inet_diag_sockid"
> +are as follows:
> +.TP
> +.I idiag_sport
> +The source port.
> +.TP
> +.I idiag_dport
> +The destination port.
> +.TP
> +.I idiag_src
> +The source address.
> +.TP
> +.I idiag_dst
> +The destination address.
> +.TP
> +.I idiag_if
> +The interface number the socket is bound to.
> +.TP
> +.I idiag_cookie
> +This is an array of opaque identifiers that could be used along with
> +other fields of this structure to specify an individual socket.
> +It is ignored when querying for a list of sockets, as well as
> +when all its elements are set to \-1.
> +.PP
> +The response to a query for IPv4 or IPv6 sockets is represented as an array of
> +
> +.in +4n
> +.nf
> +struct inet_diag_msg {
> +    __u8    idiag_family;
> +    __u8    idiag_state;
> +    __u8    idiag_timer;
> +    __u8    idiag_retrans;
> +
> +    struct inet_diag_sockid id;
> +
> +    __u32   idiag_expires;
> +    __u32   idiag_rqueue;
> +    __u32   idiag_wqueue;
> +    __u32   idiag_uid;
> +    __u32   idiag_inode;
> +};
> +.fi
> +.in
> +
> +followed by netlink attributes.
> +.PP
> +The fields of this structure are as follows:
> +.TP
> +.I idiag_family
> +This is the same field as in
> +.IR "struct inet_diag_req_v2" .
> +.TP
> +.I idiag_state
> +This denotes socket state as in
> +.IR "struct inet_diag_req_v2" .
> +.TP
> +.I idiag_timer
> +For TCP sockets, this field describes the type of timer that is currently
> +active for the socket.  It is set to one of the following constants:
> +.RS
> +.TP
> +.B 0
> +no timer is active
> +.TP
> +.B 1
> +a retransmit timer
> +.TP
> +.B 2
> +a keep-alive timer
> +.TP
> +.B 3
> +a TIME_WAIT timer
> +.TP
> +.B 4
> +a zero window probe timer
> +.RE
> +.IP
> +.RS
> +For non-TCP sockets this field is set to 0.
> +.RE
> +.TP
> +.I idiag_retrans
> +For
> +.I idiag_timer
> +values 1, 2, and 4 this field contains the number of retransmits.  For other
> +.I idiag_timer
> +values this field is set to 0.
> +.TP
> +.I idiag_expires
> +For TCP sockets that have an active timer this field describes its expiration
> +time in milliseconds.  For other sockets this field is set to 0.
> +.TP
> +.I idiag_rqueue
> +.RS 7
> +.IP "listening sockets:" 2
> +The number of pending connections.
> +.IP "other sockets:"
> +The amount of data in incoming queue.
> +.RE
> +.TP
> +.I idiag_wqueue
> +.RS 7
> +.IP "listening sockets:" 2
> +The backlog length.
> +.IP "other sockets:"
> +The amount of memory available for sending.
> +.RE
> +.TP
> +.I idiag_uid
> +This is the socket owner UID.
> +.TP
> +.I idiag_inode
> +This is the socket inode number.
> +
> +.SS Socket memory information
> +The payload associated with
> +.B UNIX_DIAG_MEMINFO
> +and
> +.BR INET_DIAG_SKMEMINFO
> +netlink attributes is an array of the following __u32 values:
> +.TP
> +.B SK_MEMINFO_RMEM_ALLOC
> +The amount of data in receive queue.
> +.TP
> +.B SK_MEMINFO_RCVBUF
> +The receive socket buffer as set by
> +.BR SO_RCVBUF .
> +.TP
> +.B SK_MEMINFO_WMEM_ALLOC
> +The amount of data in send queue.
> +.TP
> +.B SK_MEMINFO_SNDBUF
> +The send socket buffer as set by
> +.BR SO_SNDBUF .
> +.TP
> +.B SK_MEMINFO_FWD_ALLOC
> +The amount of memory scheduled for future use (TCP only).
> +.TP
> +.B SK_MEMINFO_WMEM_QUEUED
> +The amount of data queued by TCP, but not yet sent.
> +.TP
> +.B SK_MEMINFO_OPTMEM
> +The amount of memory allocated for socket's service needs (e.g. socket
> +filter).
> +.TP
> +.B SK_MEMINFO_BACKLOG
> +The amount of packets in the backlog (not yet processed).
> +.SH CONFORMING TO
> +The NETLINK_SOCK_DIAG API is Linux-specific.
> +.SH VERSIONS
> +.B NETLINK_INET_DIAG
> +was introduced in Linux 2.6.14 and supported
> +.B AF_INET
> +and
> +.B AF_INET6
> +sockets only.  In Linux 3.3 it was renamed to
> +.B NETLINK_SOCK_DIAG
> +and extended to support
> +.B AF_UNIX
> +sockets.
> +.PP
> +.B UNIX_DIAG_MEMINFO
> +and
> +.BR INET_DIAG_SKMEMINFO
> +were introduced in Linux 3.6.
> +.SH EXAMPLE
> +The following example program prints inode number, peer's inode number,
> +and name of all UNIX domain sockets in the current namespace.
> +
> +.nf
> +#include <errno.h>
> +#include <stdio.h>
> +#include <string.h>
> +#include <unistd.h>
> +#include <sys/socket.h>
> +#include <sys/un.h>
> +#include <linux/netlink.h>
> +#include <linux/rtnetlink.h>
> +#include <linux/sock_diag.h>
> +#include <linux/unix_diag.h>
> +
> +static int
> +send_query(int fd)
> +{
> +    struct sockaddr_nl nladdr = {
> +        .nl_family = AF_NETLINK
> +    };
> +    struct
> +    {
> +        struct nlmsghdr nlh;
> +        struct unix_diag_req udr;
> +    } req = {
> +        .nlh = {
> +            .nlmsg_len = sizeof(req),
> +            .nlmsg_type = SOCK_DIAG_BY_FAMILY,
> +            .nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP
> +        },
> +        .udr = {
> +            .sdiag_family = AF_UNIX,
> +            .udiag_states = \-1,
> +            .udiag_show = UDIAG_SHOW_NAME | UDIAG_SHOW_PEER
> +        }
> +    };
> +    struct iovec iov = {
> +        .iov_base = &req,
> +        .iov_len = sizeof(req)
> +    };
> +    struct msghdr msg = {
> +        .msg_name = (void *) &nladdr,
> +        .msg_namelen = sizeof(nladdr),
> +        .msg_iov = &iov,
> +        .msg_iovlen = 1
> +    };
> +
> +    for (;;) {
> +        if (sendmsg(fd, &msg, 0) < 0) {
> +            if (errno == EINTR)
> +                continue;
> +            perror("sendmsg");
> +            return \-1;
> +        }
> +        return 0;
> +    }
> +}
> +
> +static int
> +print_diag(const struct unix_diag_msg *diag, unsigned int len)
> +{
> +    if (len < NLMSG_LENGTH(sizeof(*diag))) {
> +        fputs("short response\\n", stderr);
> +        return \-1;
> +    }
> +    if (diag\->udiag_family != AF_UNIX) {
> +        fprintf(stderr, "unexpected family %u\\n", diag\->udiag_family);
> +        return \-1;
> +    }
> +
> +    struct rtattr *attr;
> +    unsigned int rta_len = len \- NLMSG_LENGTH(sizeof(*diag));
> +    unsigned int peer = 0;
> +    size_t path_len = 0;
> +    char path[sizeof(((struct sockaddr_un *) 0)\->sun_path) + 1];
> +
> +    for (attr = (struct rtattr *) (diag + 1);
> +             RTA_OK(attr, rta_len); attr = RTA_NEXT(attr, rta_len)) {
> +        switch (attr\->rta_type) {
> +            case UNIX_DIAG_NAME:
> +                if (!path_len) {
> +                    path_len = RTA_PAYLOAD(attr);
> +                    if (path_len > sizeof(path) \- 1)
> +                        path_len = sizeof(path) \- 1;
> +                    memcpy(path, RTA_DATA(attr), path_len);
> +                    path[path_len] = '\\0';
> +                }
> +                break;
> +            case UNIX_DIAG_PEER:
> +                if (RTA_PAYLOAD(attr) >= sizeof(peer))
> +                    peer = *(unsigned int *) RTA_DATA(attr);
> +                break;
> +        }
> +    }
> +
> +    printf("inode=%u", diag->udiag_ino);
> +
> +    if (peer)
> +        printf(", peer=%u", peer);
> +
> +    if (path_len)
> +        printf(", name=%s%s", *path ? "" : "@", *path ? path : path + 1);
> +
> +    putchar('\\n');
> +    return 0;
> +}
> +
> +static int
> +receive_responses(int fd)
> +{
> +    long buf[8192 / sizeof(long)];
> +    struct sockaddr_nl nladdr = {
> +        .nl_family = AF_NETLINK
> +    };
> +    struct iovec iov = {
> +        .iov_base = buf,
> +        .iov_len = sizeof(buf)
> +    };
> +    int flags = 0;
> +
> +    for (;;) {
> +        struct msghdr msg = {
> +            .msg_name = (void *) &nladdr,
> +            .msg_namelen = sizeof(nladdr),
> +            .msg_iov = &iov,
> +            .msg_iovlen = 1
> +        };
> +
> +        ssize_t ret = recvmsg(fd, &msg, flags);
> +
> +        if (ret < 0) {
> +            if (errno == EINTR)
> +                continue;
> +            perror("recvmsg");
> +            return \-1;
> +        }
> +        if (ret == 0)
> +            return 0;
> +
> +        const struct nlmsghdr *h = (struct nlmsghdr *) buf;
> +
> +        if (!NLMSG_OK(h, ret)) {
> +            fputs("!NLMSG_OK\\n", stderr);
> +            return \-1;
> +        }
> +        for (; NLMSG_OK(h, ret); h = NLMSG_NEXT(h, ret)) {
> +            if (h\->nlmsg_type == NLMSG_DONE)
> +                return 0;
> +            if (h\->nlmsg_type == NLMSG_ERROR) {
> +                const struct nlmsgerr *err = NLMSG_DATA(h);
> +
> +                if (h\->nlmsg_len < NLMSG_LENGTH(sizeof(*err))) {
> +                    fputs("NLMSG_ERROR\\n", stderr);
> +                } else {
> +                    errno = \-err\->error;
> +                    perror("NLMSG_ERROR");
> +                }
> +                return \-1;
> +            }
> +            if (h\->nlmsg_type != SOCK_DIAG_BY_FAMILY) {
> +                fprintf(stderr, "unexpected nlmsg_type %u\\n",
> +                        (unsigned) h\->nlmsg_type);
> +                return \-1;
> +            }
> +
> +            if (print_diag(NLMSG_DATA(h), h\->nlmsg_len))
> +                return \-1;
> +        }
> +    }
> +}
> +
> +int
> +main(void)
> +{
> +    int fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_SOCK_DIAG);
> +
> +    if (fd < 0) {
> +        perror("socket");
> +        return 1;
> +    }
> +
> +    int ret = send_query(fd) || receive_responses(fd);
> +
> +    close(fd);
> +    return ret;
> +}
> +.fi
> +.SH SEE ALSO
> +.BR netlink (3),
> +.BR rtnetlink (3),
> +.BR netlink (7),
> +.BR tcp (7)
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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