sock_diag.7: New page documenting NETLINK_SOCK_DIAG interface

From: Pavel Emelyanov <[email protected]>

Cowritten-by Dmitry V. Levin <ldv-u2l5PoMzF/[email protected]>

Signed-off-by Pavel Emelyanov <[email protected]>

Signed-off-by Dmitry V. Levin <ldv-u2l5PoMzF/[email protected]>

---
 man7/sock_diag.7 | 632 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 632 insertions(+)
 create mode 100644 man7/sock_diag.7

man7/sock_diag.7 new file +30 -0

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@@ -0,0 +1,632 @@
+.\" Copyright (c) 2016 Pavel Emelyanov <[email protected]>
+.\" Copyright (c) 2016 Dmitry V. Levin <ldv-u2l5PoMzF/[email protected]>
+.\"
+.\" %%%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 2016-03-14 "Linux" "Linux Programmer's Manual"
+.SH NAME
+sock_diag \- querying information about sockets
+.SH SYNOPSIS
+.nf
+.B #include <sys/socket.h>
+.B #include <linux/sock_diag.h>

man7/sock_diag.7 new file +13 -0

+
+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's only the 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 auto-bound ones (e.g. connected).  This is the same set of sockets that
+is available via
+.IR /proc/net/unix ,
+.IR /proc/net/tcp ,

man7/sock_diag.7 new file +6 -0

+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 {

man7/sock_diag.7 new file +67 -0

+and to 0 otherwise.
+.PP
+If
+.I nlmsg_flags
+field of the
+.I "struct nlmsghdr"
+header has
+.BR NLM_F_DUMP
+flag set, then 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
+This is a protocol family, it should be set to
+.BR PF_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 <<

man7/sock_diag.7 new file +120 -0

+.TP
+.I udiag_show
+This is a set of flags defining which information to report.
+Each requested info 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 name of the socket
+to which it 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 node.
+.IP
+.I udiag_vfs_ino
+The inode number of the corresponding on-disk socket node.
+.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 which equals to
+.B UNIX_DIAG_ICONS
+array length.
+.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:

man7/sock_diag.7 new file +114 -0

+.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_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 udiag_ino
+This is the socket inode number.
+.PP
+.I udiag_family
+.PD 0
+.PP
+.I pad
+.TP
+.I udiag_cookie
+These fields have the same meaning as in
+.IR "struct unix_diag_req" .
+.PD
+
+.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 PF_INET
+or
+.B PF_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

man7/sock_diag.7 new file +7 -0

+.B INET_DIAG_MEMINFO
+The payload associated with this attribute is represented in the following
+structure:
+
+.in +4n
+.nf
+struct inet_diag_meminfo {

man7/sock_diag.7 new file +30 -0

+.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

man7/sock_diag.7 new file +32 -0

+.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

man7/sock_diag.7 new file +61 -0

+.PD
+.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_SOCK_DIAG

Hello Dmitry

Thanks for taking the time to work on this!

I will probably have more comments, for a future draft, but here are a few initial comments. Could you take a look and send a new draft?

Quoted 46 lines · Dmitry V. Levin

From: Pavel Emelyanov <[email protected]>

Cowritten-by Dmitry V. Levin <ldv-u2l5PoMzF/[email protected]>

Signed-off-by Pavel Emelyanov <[email protected]>

Signed-off-by Dmitry V. Levin <ldv-u2l5PoMzF/[email protected]>

---
 man7/sock_diag.7 | 632 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 632 insertions(+)
 create mode 100644 man7/sock_diag.7

man7/sock_diag.7 new file +30 -0

new file mode 100644
index 0000000..d1be9cf
@@ -0,0 +1,632 @@
+.\" Copyright (c) 2016 Pavel Emelyanov <[email protected]>
+.\" Copyright (c) 2016 Dmitry V. Levin <ldv-u2l5PoMzF/[email protected]>
+.\"
+.\" %%%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 2016-03-14 "Linux" "Linux Programmer's Manual"
+.SH NAME
+sock_diag \- querying information about sockets
+.SH SYNOPSIS
+.nf
+.B #include <sys/socket.h>
+.B #include <linux/sock_diag.h>

man7/sock_diag.7 line 40

Quoted 10 lines

man7/sock_diag.7 new file +10 -0

+.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 querying information
+about sockets of various protocol families from the kernel.  This subsystem
+can be used to query information about individual sockets or request a list of
+those.

Sorry, it's not clear what "those" refers to. Could you replace with a noun?

man7/sock_diag.7 line 43

Quoted 3 lines

man7/sock_diag.7 new file +3 -0

+
+In the request the caller can specify the additional information it would
+like to query about the socket, e.g. memory info or family-specific stuff.

s/query/obtain/

Quoted 13 lines

man7/sock_diag.7 new file +13 -0

+
+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's only the 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 auto-bound ones (e.g. connected).  This is the same set of sockets that
+is available via
+.IR /proc/net/unix ,
+.IR /proc/net/tcp ,

man7/sock_diag.7 line 66

Quoted 10 lines

man7/sock_diag.7 new file +10 -0

+.IR /proc/net/udp ,
+etc.
+
+.SS Request
+The request starts with
+.I "struct nlmsghdr"
+header that has
+.I nlmsg_type
+field set to
+.BR SOCK_DIAG_BY_FAMILY .

I think it might be useful to either show the nlmsghdr structure here, or add a note to tell the reader that this structure defintion is hown in netlink(7).

Quoted 6 lines

man7/sock_diag.7 new file +6 -0

+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 {

man7/sock_diag.7 line 82

Quoted 10 lines

man7/sock_diag.7 new file +10 -0

+    __u8 sdiag_family;
+    __u8 sdiag_protocol;
+};
+.fi
+.in
+.PP
+The fields of this structure are as follows:
+.TP
+.I sdiag_family
+The protocol family of querying sockets.  It should be set to the appropriate

The meaning of "querying sockets" is unclear. Can you reword/elaborate?

man7/sock_diag.7 line 83

Quoted 1 line

man7/sock_diag.7 new file +1 -0

+.B PF_*

AF_* constant, I would say. POSIX doesn't talk about PF*, and in practice there's always a one to one relationship between AF_* and PF_*, so all other man pages use AF_*.

man7/sock_diag.7 line 92

Quoted 9 lines

man7/sock_diag.7 new file +9 -0

+constant.
+.TP
+.I sdiag_protocol
+Depends on
+.IR sdiag_family .
+It should be set to the appropriate
+.B IPPROTO_*
+constant for
+.B PF_INET

AF_...

man7/sock_diag.7 line 94

Quoted 2 lines

man7/sock_diag.7 new file +2 -0

+and
+.BR PF_INET6,

AF_...

Quoted 67 lines

man7/sock_diag.7 new file +67 -0

+and to 0 otherwise.
+.PP
+If
+.I nlmsg_flags
+field of the
+.I "struct nlmsghdr"
+header has
+.BR NLM_F_DUMP
+flag set, then 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
+This is a protocol family, it should be set to
+.BR PF_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 <<

man7/sock_diag.7 line 171

Quoted 10 lines

man7/sock_diag.7 new file +10 -0

+.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 for a bulk dump.

The meaning of "bulk dump" is not clear.

Quoted 120 lines

man7/sock_diag.7 new file +120 -0

+.TP
+.I udiag_show
+This is a set of flags defining which information to report.
+Each requested info 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 name of the socket
+to which it 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 node.
+.IP
+.I udiag_vfs_ino
+The inode number of the corresponding on-disk socket node.
+.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 which equals to
+.B UNIX_DIAG_ICONS
+array length.
+.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:

man7/sock_diag.7 line 301

Quoted 10 lines

man7/sock_diag.7 new file +10 -0

+.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 service field, both its cells should be set to \-1.

What does "service field" mean? I think this needs to be clarified.

Quoted 114 lines

man7/sock_diag.7 new file +114 -0

+.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_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 udiag_ino
+This is the socket inode number.
+.PP
+.I udiag_family
+.PD 0
+.PP
+.I pad
+.TP
+.I udiag_cookie
+These fields have the same meaning as in
+.IR "struct unix_diag_req" .
+.PD
+
+.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 PF_INET
+or
+.B PF_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

man7/sock_diag.7 line 425

Quoted 10 lines

man7/sock_diag.7 new file +10 -0

+.B IPPROTO_UDPLITE
+.RE
+.PD
+.TP
+.I idiag_ext
+This is a set of flags defining which extended information to report.
+Each requested info is reported back as a netlink attribute as described
+below:
+.RS
+.IP "" 2

Replace the last line with

.TP

man7/sock_diag.7 line 429

Quoted 4 lines

man7/sock_diag.7 new file +4 -0

+.B INET_DIAG_TOS
+The payload associated with this attribute is a __u8 value
+which is the TOS of the socket.
+.IP

.TP

man7/sock_diag.7 line 437

Quoted 8 lines

man7/sock_diag.7 new file +8 -0

+.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.
+.IP

.TP

Quoted 7 lines

man7/sock_diag.7 new file +7 -0

+.B INET_DIAG_MEMINFO
+The payload associated with this attribute is represented in the following
+structure:
+
+.in +4n
+.nf
+struct inet_diag_meminfo {

man7/sock_diag.7 line 454

Quoted 10 lines

man7/sock_diag.7 new file +10 -0

+    __u32 idiag_rmem;
+    __u32 idiag_wmem;
+    __u32 idiag_fmem;
+    __u32 idiag_tmem;
+};
+.fi
+.in
+
+The fields of this structure are as follows:
+.PD 0

Delete previous line.

man7/sock_diag.7 line 455

Quoted 1 line

man7/sock_diag.7 new file +1 -0

+.RS 2

Make the last line

.RS

man7/sock_diag.7 line 456

Quoted 1 line

man7/sock_diag.7 new file +1 -0

+.IP "" 2

Change the last line to

.TP 12

man7/sock_diag.7 line 459

Quoted 3 lines

man7/sock_diag.7 new file +3 -0

+.I idiag_rmem
+The amount of data in the receive queue.
+.IP

.TP

man7/sock_diag.7 line 462

Quoted 3 lines

man7/sock_diag.7 new file +3 -0

+.I idiag_wmem
+The amount of data that is queued by TCP but not yet sent.
+.IP

.TP

man7/sock_diag.7 line 465

Quoted 3 lines

man7/sock_diag.7 new file +3 -0

+.I idiag_fmem
+The amount of memory scheduled for future use (TCP only).
+.IP

.TP

man7/sock_diag.7 line 469

Quoted 4 lines

man7/sock_diag.7 new file +4 -0

+.I idiag_tmem
+The amount of data in send queue.
+.RE
+.PD

Remove previous line

man7/sock_diag.7 line 470

Quoted 1 line

man7/sock_diag.7 new file +1 -0

+.IP

.TP

man7/sock_diag.7 line 474

Quoted 4 lines

man7/sock_diag.7 new file +4 -0

+.B INET_DIAG_SKMEMINFO
+The payload associated with this attribute is an array of __u32 values
+described below in "Socket memory information" subsection.
+.IP

.TP

man7/sock_diag.7 line 479

Quoted 5 lines

man7/sock_diag.7 new file +5 -0

+.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" .
+.IP

.TP

Quoted 30 lines

man7/sock_diag.7 new file +30 -0

+.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

man7/sock_diag.7 line 519

Quoted 10 lines

man7/sock_diag.7 new file +10 -0

+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 a service field, both its cells should be set to \-1.

Again, I think the meaning of "service" filed needs to be clarified.

Quoted 32 lines

man7/sock_diag.7 new file +32 -0

+.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

man7/sock_diag.7 line 561

Quoted 10 lines

man7/sock_diag.7 new file +10 -0

+.IR "struct inet_diag_req_v2" .
+.PP
+.I idiag_timer
+.PD 0
+.PP
+.I idiag_retrans
+.TP
+.I idiag_expires
+These fields are TCP-only and represent the timeout that is currently
+in action for particular TCP state (0 for established sockets).

Can you elaborate with an example of a state that has a timeout. (Is this just TIME_WAIT, or others also?)

Quoted 61 lines

man7/sock_diag.7 new file +61 -0

+.PD
+.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_SOCK_DIAG

man7/sock_diag.7 line 632

Quoted 10 lines

man7/sock_diag.7 new file +10 -0

+was introduced in Linux 3.3.
+.PP
+.B UNIX_DIAG_MEMINFO
+and
+.BR INET_DIAG_SKMEMINFO
+were introduced in Linux 3.6.
+.SH SEE ALSO
+.BR netlink (3),
+.BR rtnetlink (3),
+.BR netlink (7)

In the next iteration, I think it would be simplest to just include the example program in the same patch.

Thanks,

Michael

Hello Dmitry, Pavel,

Ping!

Cheers,

Michael

Quoted 748 lines · Michael Kerrisk (man-pages)

Hello Dmitry

Thanks for taking the time to work on this!

I will probably have more comments, for a future draft, but here are a few initial comments. Could you take a look and send a new draft?

Quoted 46 lines · Dmitry V. Levin

From: Pavel Emelyanov <[email protected]>

Cowritten-by Dmitry V. Levin <ldv-u2l5PoMzF/[email protected]>

Signed-off-by Pavel Emelyanov <[email protected]>

Signed-off-by Dmitry V. Levin <ldv-u2l5PoMzF/[email protected]>

---
 man7/sock_diag.7 | 632 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 632 insertions(+)
 create mode 100644 man7/sock_diag.7

man7/sock_diag.7 new file +30 -0

new file mode 100644
index 0000000..d1be9cf
@@ -0,0 +1,632 @@
+.\" Copyright (c) 2016 Pavel Emelyanov <[email protected]>
+.\" Copyright (c) 2016 Dmitry V. Levin <ldv-u2l5PoMzF/[email protected]>
+.\"
+.\" %%%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 2016-03-14 "Linux" "Linux Programmer's Manual"
+.SH NAME
+sock_diag \- querying information about sockets
+.SH SYNOPSIS
+.nf
+.B #include <sys/socket.h>
+.B #include <linux/sock_diag.h>

man7/sock_diag.7 line 40

Quoted 10 lines

man7/sock_diag.7 new file +10 -0

+.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 querying information
+about sockets of various protocol families from the kernel.  This subsystem
+can be used to query information about individual sockets or request a list of
+those.

Sorry, it's not clear what "those" refers to. Could you replace with a noun?

man7/sock_diag.7 line 43

Quoted 3 lines

man7/sock_diag.7 new file +3 -0

+
+In the request the caller can specify the additional information it would
+like to query about the socket, e.g. memory info or family-specific stuff.

s/query/obtain/

Quoted 13 lines

man7/sock_diag.7 new file +13 -0

+
+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's only the 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 auto-bound ones (e.g. connected).  This is the same set of sockets that
+is available via
+.IR /proc/net/unix ,
+.IR /proc/net/tcp ,

man7/sock_diag.7 line 66

Quoted 10 lines

man7/sock_diag.7 new file +10 -0

+.IR /proc/net/udp ,
+etc.
+
+.SS Request
+The request starts with
+.I "struct nlmsghdr"
+header that has
+.I nlmsg_type
+field set to
+.BR SOCK_DIAG_BY_FAMILY .

I think it might be useful to either show the nlmsghdr structure here, or add a note to tell the reader that this structure defintion is hown in netlink(7).

Quoted 6 lines

man7/sock_diag.7 new file +6 -0

+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 {

man7/sock_diag.7 line 82

Quoted 10 lines

man7/sock_diag.7 new file +10 -0

+    __u8 sdiag_family;
+    __u8 sdiag_protocol;
+};
+.fi
+.in
+.PP
+The fields of this structure are as follows:
+.TP
+.I sdiag_family
+The protocol family of querying sockets.  It should be set to the appropriate

The meaning of "querying sockets" is unclear. Can you reword/elaborate?

man7/sock_diag.7 line 83

Quoted 1 line

man7/sock_diag.7 new file +1 -0

+.B PF_*

AF_* constant, I would say. POSIX doesn't talk about PF*, and in practice there's always a one to one relationship between AF_* and PF_*, so all other man pages use AF_*.

man7/sock_diag.7 line 92

Quoted 9 lines

man7/sock_diag.7 new file +9 -0

+constant.
+.TP
+.I sdiag_protocol
+Depends on
+.IR sdiag_family .
+It should be set to the appropriate
+.B IPPROTO_*
+constant for
+.B PF_INET

AF_...

man7/sock_diag.7 line 94

Quoted 2 lines

man7/sock_diag.7 new file +2 -0

+and
+.BR PF_INET6,

AF_...

Quoted 67 lines

man7/sock_diag.7 new file +67 -0

+and to 0 otherwise.
+.PP
+If
+.I nlmsg_flags
+field of the
+.I "struct nlmsghdr"
+header has
+.BR NLM_F_DUMP
+flag set, then 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
+This is a protocol family, it should be set to
+.BR PF_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 <<

man7/sock_diag.7 line 171

Quoted 10 lines

man7/sock_diag.7 new file +10 -0

+.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 for a bulk dump.

The meaning of "bulk dump" is not clear.

Quoted 120 lines

man7/sock_diag.7 new file +120 -0

+.TP
+.I udiag_show
+This is a set of flags defining which information to report.
+Each requested info 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 name of the socket
+to which it 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 node.
+.IP
+.I udiag_vfs_ino
+The inode number of the corresponding on-disk socket node.
+.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 which equals to
+.B UNIX_DIAG_ICONS
+array length.
+.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:

man7/sock_diag.7 line 301

Quoted 10 lines

man7/sock_diag.7 new file +10 -0

+.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 service field, both its cells should be set to \-1.

What does "service field" mean? I think this needs to be clarified.

Quoted 114 lines

man7/sock_diag.7 new file +114 -0

+.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_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 udiag_ino
+This is the socket inode number.
+.PP
+.I udiag_family
+.PD 0
+.PP
+.I pad
+.TP
+.I udiag_cookie
+These fields have the same meaning as in
+.IR "struct unix_diag_req" .
+.PD
+
+.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 PF_INET
+or
+.B PF_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

man7/sock_diag.7 line 425

Quoted 10 lines

man7/sock_diag.7 new file +10 -0

+.B IPPROTO_UDPLITE
+.RE
+.PD
+.TP
+.I idiag_ext
+This is a set of flags defining which extended information to report.
+Each requested info is reported back as a netlink attribute as described
+below:
+.RS
+.IP "" 2

Replace the last line with

.TP

man7/sock_diag.7 line 429

Quoted 4 lines

man7/sock_diag.7 new file +4 -0

+.B INET_DIAG_TOS
+The payload associated with this attribute is a __u8 value
+which is the TOS of the socket.
+.IP

.TP

man7/sock_diag.7 line 437

Quoted 8 lines

man7/sock_diag.7 new file +8 -0

+.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.
+.IP

.TP

Quoted 7 lines

man7/sock_diag.7 new file +7 -0

+.B INET_DIAG_MEMINFO
+The payload associated with this attribute is represented in the following
+structure:
+
+.in +4n
+.nf
+struct inet_diag_meminfo {

man7/sock_diag.7 line 454

Quoted 10 lines

man7/sock_diag.7 new file +10 -0

+    __u32 idiag_rmem;
+    __u32 idiag_wmem;
+    __u32 idiag_fmem;
+    __u32 idiag_tmem;
+};
+.fi
+.in
+
+The fields of this structure are as follows:
+.PD 0

Delete previous line.

man7/sock_diag.7 line 455

Quoted 1 line

man7/sock_diag.7 new file +1 -0

+.RS 2

Make the last line

.RS

man7/sock_diag.7 line 456

Quoted 1 line

man7/sock_diag.7 new file +1 -0

+.IP "" 2

Change the last line to

.TP 12

man7/sock_diag.7 line 459

Quoted 3 lines

man7/sock_diag.7 new file +3 -0

+.I idiag_rmem
+The amount of data in the receive queue.
+.IP

.TP

man7/sock_diag.7 line 462

Quoted 3 lines

man7/sock_diag.7 new file +3 -0

+.I idiag_wmem
+The amount of data that is queued by TCP but not yet sent.
+.IP

.TP

man7/sock_diag.7 line 465

Quoted 3 lines

man7/sock_diag.7 new file +3 -0

+.I idiag_fmem
+The amount of memory scheduled for future use (TCP only).
+.IP

.TP

man7/sock_diag.7 line 469

Quoted 4 lines

man7/sock_diag.7 new file +4 -0

+.I idiag_tmem
+The amount of data in send queue.
+.RE
+.PD

Remove previous line

man7/sock_diag.7 line 470

Quoted 1 line

man7/sock_diag.7 new file +1 -0

+.IP

.TP

man7/sock_diag.7 line 474

Quoted 4 lines

man7/sock_diag.7 new file +4 -0

+.B INET_DIAG_SKMEMINFO
+The payload associated with this attribute is an array of __u32 values
+described below in "Socket memory information" subsection.
+.IP

.TP

man7/sock_diag.7 line 479

Quoted 5 lines

man7/sock_diag.7 new file +5 -0

+.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" .
+.IP

.TP

Quoted 30 lines

man7/sock_diag.7 new file +30 -0

+.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

man7/sock_diag.7 line 519

Quoted 10 lines

man7/sock_diag.7 new file +10 -0

+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 a service field, both its cells should be set to \-1.

Again, I think the meaning of "service" filed needs to be clarified.

Quoted 32 lines

man7/sock_diag.7 new file +32 -0

+.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

man7/sock_diag.7 line 561

Quoted 10 lines

man7/sock_diag.7 new file +10 -0

+.IR "struct inet_diag_req_v2" .
+.PP
+.I idiag_timer
+.PD 0
+.PP
+.I idiag_retrans
+.TP
+.I idiag_expires
+These fields are TCP-only and represent the timeout that is currently
+in action for particular TCP state (0 for established sockets).

Can you elaborate with an example of a state that has a timeout. (Is this just TIME_WAIT, or others also?)

Quoted 61 lines

man7/sock_diag.7 new file +61 -0

+.PD
+.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_SOCK_DIAG

man7/sock_diag.7 line 632

Quoted 10 lines

man7/sock_diag.7 new file +10 -0

+was introduced in Linux 3.3.
+.PP
+.B UNIX_DIAG_MEMINFO
+and
+.BR INET_DIAG_SKMEMINFO
+were introduced in Linux 3.6.
+.SH SEE ALSO
+.BR netlink (3),
+.BR rtnetlink (3),
+.BR netlink (7)

In the next iteration, I think it would be simplest to just include the example program in the same patch.

Thanks,

Michael

Hello Dmitry

Thanks for taking the time to work on this!

I will probably have more comments, for a future draft, but here are a few initial comments. Could you take a look and send a new draft?

Hi,

Quoted 2 lines · Michael Kerrisk (man-pages)

Hello Dmitry

Quoted 4 lines

Thanks for taking the time to work on this!

I will probably have more comments, for a future draft, but here are a few initial comments. Could you take a look and send a new draft?

Unfortunately, the new draft took much longer than I expected, but here it is.

.\" Copyright (c) 2016 Pavel Emelyanov <[email protected]> .\" Copyright (c) 2016 Dmitry V. Levin <ldv-u2l5PoMzF/[email protected]> .\"
.\" %%%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 2016-12-06 "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 auto-bound ones (e.g. connected). 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 name of the socket to which it 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 node.

.IP
.I udiag_vfs_ino
The inode number of the corresponding on-disk socket node.

.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 which equals to
.B UNIX_DIAG_ICONS
array length.

.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 <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)

Hello Dmitry,

Quoted 10 lines · Dmitry V. Levin

Hi,

Quoted 6 lines · Michael Kerrisk (man-pages)

Hello Dmitry

Thanks for taking the time to work on this!

I will probably have more comments, for a future draft, but here are a few initial comments. Could you take a look and send a new draft?

Quoted 2 lines

Unfortunately, the new draft took much longer than I expected, but here it is.

Thank you! I have just a few more questions. The page could still do with some polishing, but it's got a lot of valuable stuff, and I'll accept it already, but would be happy if you could look at the new questions, and perhaps lightly revise the page.