NAME

iounit − return size of atomic I/O unit for file descriptor

SYNOPSIS

include "sys.m"; sys := load Sys Sys->PATH;
 
iounit:fn(fd: ref FD): int;

DESCRIPTION

Reads and writes of files are transmitted using the 9P protocol (see 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.

The iounit system call returns the I/O unit size for the open file fd. Certain file descriptors, particularly those associated with devices, may have no specific I/O unit, in which case iounit will return zero. 

SOURCE

/emu/port/inferno.c
/os/port/inferno.c

SEE ALSO

sys-dup(2), read(5)

DIAGNOSTICS

Returns zero if any error occurs or if the I/O unit size of the fd is unspecified or unknown.