1 .TH SENDFD 3
2 .SH NAME
3 sendfd, recvfd \- pass file descriptors along Unix domain sockets
4 .SH SYNOPSIS
5 .B
6 #include <u.h>
7 .PP
8 .B
9 #include <libc.h>
10 .PP
11 .B
12 int	sendfd(int socket, int fd)
13 .PP
14 .B
15 int	recvfd(int socket)
16 .SH DESCRIPTION
17 .I Recvfd
18 and
19 .I sendfd
20 can be used to pass an open file descriptor over
21 a Unix domain socket from one process to another.
22 Since
23 .MR pipe (3)
24 is implemented with
25 .MR socketpair (2)
26 instead of
27 .MR pipe (2) ,
28 .I socket
29 can be a file descriptor obtained from
30 .MR pipe (3) .
31 .PP
32 .I Sendfd
33 sends the file descriptor
34 .I fd
35 along the socket to a process calling
36 .I recvfd 
37 on the other end.
38 .PP
39 It is assumed that the two sides have coordinated
40 and agreed to transfer a file descriptor already, so
41 that the
42 .I sendfd
43 is met with a
44 .I recvfd
45 instead of an ordinary
46 .IR read .
47 .PP
48 The file descriptor number may change on its way
49 between processes, but the kernel structure it represents
50 will not.
51 .SH SOURCE
52 .B \*9/src/lib9/sendfd.c
53 .SH SEE ALSO
54 .MR socketpair (2) ,
55 .I sendmsg
56 in
57 .MR send (2)