ref: 87d72e7e8614d96b4f61adae5fb05b0534231c4c
dir: /man/2/sys-iounit/
.TH SYS-IOUNIT 2 .SH NAME iounit \- return size of atomic I/O unit for file descriptor .SH SYNOPSIS .EX include "sys.m"; sys := load Sys Sys->PATH; iounit: fn(fd: ref FD): int; .EE .SH DESCRIPTION Reads and writes of files are transmitted using the 9P protocol (see .IR intro (5)) and in general, operations involving large amounts of data must be broken into smaller pieces by the operating system. The `I/O unit' associated with each file descriptor records the maximum size, in bytes, that may be read or written without breaking up the transfer. .PP The .B iounit system call returns the I/O unit size for the open file .IR fd . Certain file descriptors, particularly those associated with devices, may have no specific I/O unit, in which case .B iounit will return zero. .SH SOURCE .B /emu/port/inferno.c .br .B /os/port/inferno.c .SH SEE ALSO .IR sys-dup (2), .IR read (5) .SH DIAGNOSTICS Returns zero if any error occurs or if the I/O unit size of the fd is unspecified or unknown.