xref: /dragonfly/lib/libc/net/getifaddrs.3 (revision dda92f98) 
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25.\" $FreeBSD: src/lib/libc/net/getifaddrs.3,v 1.10 2005/02/09 18:03:13 ru Exp $
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27.Dd September 12, 2019
28.Dt GETIFADDRS 3
29.Os
30.Sh NAME
31.Nm getifaddrs
32.Nd get interface addresses
33.Sh LIBRARY
34.Lb libc
35.Sh SYNOPSIS
36.In sys/types.h
37.In sys/socket.h
38.In ifaddrs.h
39.Ft int
40.Fn getifaddrs "struct ifaddrs **ifap"
41.Ft void
42.Fn freeifaddrs "struct ifaddrs *ifp"
43.Sh DESCRIPTION
44The
45.Fn getifaddrs
46function stores a reference to a linked list of the network interfaces
47on the local machine in the memory referenced by
48.Fa ifap .
49The list consists of
50.Nm ifaddrs
51structures, as defined in the include file
52.In ifaddrs.h .
53The
54.Nm ifaddrs
55structure contains at least the following entries:
56.Bd -literal
57    struct ifaddrs   *ifa_next;         /* Pointer to next struct */
58    char             *ifa_name;         /* Interface name */
59    u_int             ifa_flags;        /* Interface flags */
60    struct sockaddr  *ifa_addr;         /* Interface address */
61    struct sockaddr  *ifa_netmask;      /* Interface netmask */
62    struct sockaddr  *ifa_dstaddr;      /* P2P interface destination */
63    void             *ifa_data;         /* Address specific data */
64    u_int             ifa_addrflags;    /* Family specific address flags */
65.Ed
66.Pp
67The
68.Fa ifa_next
69field contains a pointer to the next structure on the list.
70This field is
71.Dv NULL
72in last structure on the list.
73.Pp
74The
75.Fa ifa_name
76field contains the interface name.
77.Pp
78The
79.Fa ifa_flags
80field contains the interface flags, as set by
81.Xr ifconfig 8
82utility.
83.Pp
84The
85.Fa ifa_addr
86field references either the address of the interface or the link level
87address of the interface, if one exists, otherwise it is NULL.
88(The
89.Fa sa_family
90field of the
91.Fa ifa_addr
92field should be consulted to determine the format of the
93.Fa ifa_addr
94address.)
95.Pp
96The
97.Fa ifa_netmask
98field references the netmask associated with
99.Fa ifa_addr ,
100if one is set, otherwise it is NULL.
101.Pp
102The
103.Fa ifa_dstaddr
104field references the destination address on a P2P interface,
105if one exists, otherwise it is NULL.
106.Pp
107The
108.Fa ifa_broadaddr
109field,
110which should only be referenced for non-P2P interfaces,
111references the broadcast address associated with
112.Fa ifa_addr ,
113if one exists, otherwise it is NULL.
114It is really just another name for
115.Fa ifa_dstaddr .
116.Pp
117The
118.Fa ifa_addrflags
119field contains the address flags, which are specific to the address family.
120.Pp
121The
122.Fa ifa_data
123field references address family specific data.
124For
125.Dv AF_LINK
126addresses it contains a pointer to the
127.Vt struct if_data
128(as defined in include file
129.In net/if.h )
130which contains various interface attributes and statistics.
131For all other address families, it contains a pointer to the
132.Vt struct ifa_data
133(as defined in include file
134.In net/if.h )
135which contains per-address interface statistics.
136.Pp
137The data returned by
138.Fn getifaddrs
139is dynamically allocated and should be freed using
140.Fn freeifaddrs
141when no longer needed.
142.Sh RETURN VALUES
143.Rv -std getifaddrs
144.Sh ERRORS
145The
146.Fn getifaddrs
147may fail and set
148.Va errno
149for any of the errors specified for the library routines
150.Xr ioctl 2 ,
151.Xr socket 2 ,
152.Xr malloc 3
153or
154.Xr sysctl 3 .
155.Sh SEE ALSO
156.Xr ioctl 2 ,
157.Xr socket 2 ,
158.Xr sysctl 3 ,
159.Xr networking 4 ,
160.Xr ifconfig 8
161.Sh HISTORY
162The
163.Nm
164implementation first appeared in BSDi
165.Bsx .
166.Pp
167.Fa if_addrflags
168was added in
169.Nx 8.0 .
170.Sh BUGS
171If both
172.In net/if.h
173and
174.In ifaddrs.h
175are being included,
176.In net/if.h
177.Em must
178be included before
179.In ifaddrs.h .
180