Subversion Repositories planix.SVN

Rev

Rev 34 | Details | Compare with Previous | Last modification | View Log | RSS feed

Rev Author Line No. Line
2 - 1 
.TH IOUNIT 2
2 
.SH NAME
3 
iounit \- return size of atomic I/O unit for file descriptor
4 
.SH SYNOPSIS
5 
.B #include <u.h>
6 
.br
7 
.B #include <libc.h>
8 
.PP
9 
.B
10 
int iounit(int fd)
11 
.SH DESCRIPTION
12 
Reads and writes of files are transmitted using the 9P protocol (see
13 
.IR intro (5))
14 
and in general, operations involving large amounts of data must be
15 
broken into smaller pieces by the operating system.
16 
The `I/O unit' associated with each file descriptor records the maximum
17 
size, in bytes, that may be read or written without breaking up the transfer.
18 
.PP
19 
The
20 
.I iounit
21 
routine uses the
22 
.IR dup (3)
23 
interface to discover the I/O unit size for the file descriptor
24 
.I fd
25 
and returns its value.
26 
Certain file descriptors, particularly those associated with devices, may
27 
have no specific I/O unit, in which case
28 
.I iounit
29 
will return
30 
.BR 0 .
31 
.SH SOURCE
32 
.B /sys/src/libc/9sys
33 
.SH SEE ALSO
34 
.IR dup (3),
35 
.IR read (5)
36 
.SH DIAGNOSTICS
37 
Returns zero if any error occurs or if the I/O unit size of the fd is unspecified or unknown.