ref: a1bea530d1d28fb1ae27d50f56a2f5fb6c92e3a3
dir: /sys/man/2/iounit/
.TH IOUNIT 2 .SH NAME iounit \- return size of atomic I/O unit for file descriptor .SH SYNOPSIS .B #include <u.h> .br .B #include <libc.h> .PP .B int iounit(int fd) .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 .I iounit routine uses the .IR dup (3) interface to discover the I/O unit size for the file descriptor .I fd and returns its value. Certain file descriptors, particularly those associated with devices, may have no specific I/O unit, in which case .I iounit will return .BR 0 . .SH SOURCE .B /sys/src/libc/9sys .SH SEE ALSO .IR dup (3), .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.