Hi, On Mon, Apr 04, 2016 at 08:34:47PM +1200, Michael Kerrisk (man-pages) wrote: > 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? Unfortunately, the new draft took much longer than I expected, but here it is. -- ldv
.\" Copyright (c) 2016 Pavel Emelyanov <xemul@xxxxxxxxxxxxx> .\" Copyright (c) 2016 Dmitry V. Levin <ldv@xxxxxxxxxxxx> .\" .\" %%%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)
