1 .TH READV 3
2 .SH NAME
3 readv, writev, preadv, pwritev \- scatter/gather read and write
4 .SH SYNOPSIS
5 .B #include <u.h>
6 .br
7 .B #include <libc.h>
8 .PP
9 .nf
10 .ft L
11 typedef
12 struct IOchunk
13 {
14 	void		*addr;
15 	ulong	len;
16 } IOchunk;
17 .fi
18 .PP
19 .B
20 long readv(int fd, IOchunk *io, int nio)
21 .PP
22 .B
23 long preadv(int fd, IOchunk *io, int nio, vlong off)
24 .PP
25 .B
26 long writev(int fd, IOchunk *io, int nio)
27 .PP
28 .B
29 long pwritev(int fd, IOchunk *io, int nio, vlong off)
30 .SH DESCRIPTION
31 These functions supplement the standard read and write operations of
32 .IR read (3)
33 with facilities for scatter/gather I/O.
34 The set of I/O buffers is collected into an array of
35 .B IOchunk
36 structures passed as an argument.
37 .PP
38 .I Readv
39 reads data from
40 .I fd
41 and returns the total number of bytes received.
42 The received data is stored in the successive
43 .I nio
44 elements of the
45 .B IOchunk
46 array, storing
47 .IB io [0].len
48 bytes at
49 .IB io [0].addr\f1,
50 the next
51 .IB io [1].len
52 at
53 .IB io [1].addr\f1,
54 and so on.
55 .I Preadv
56 does the same, but implicitly seeks to I/O offset
57 .I off
58 by analogy with
59 .IR readv .
60 .PP
61 .I Writev
62 and
63 .I pwritev
64 are the analogous write routines.
65 .SH SOURCE
66 .B /usr/local/plan9/src/libc/9sys/readv.c
67 .br
68 .B /usr/local/plan9/src/libc/9sys/writev.c
69 .SH SEE ALSO
70 .IR intro (3),
71 .IR read (3)
72 .SH DIAGNOSTICS
73 These functions set
74 .IR errstr .
75 .SH BUGS
76 The implementations use
77 .IR malloc (3)
78 to build a single buffer for a standard call to
79 .B read
80 or
81 .BR write .
82 They are placeholders for possible future system calls.