.TH ZIOREAD 2
.SH NAME
zioread, ziowrite, ziopread, ziopwrite, ziofree \- zero-copy read and write
.SH SYNOPSIS
.B #include <u.h>
.br
.B #include <libc.h>
.PP
.nf
.ft L
typedef struct Zio Zio;
struct Zio
{
	void*	data;
	ulong	size;
};
.fi
.PP
.B
int ziopread(int fd, Zio io[], int nio, usize count, vlong offset);
.PP
.B
int ziopwrite(int fd, Zio io[], int nio, vlong offset);
.PP
.B
int zioread(int fd, Zio io[], int nio, usize count);
.PP
.B
int ziowrite(int fd, Zio io[], int nio);
.PP
.B
void ziofree(Zio io[], int nio);
.SH DESCRIPTION
These functions supplement the standard read and write operations of
.IR read (2)
with facilities for zero-copy I/O.
The set of I/O buffers used should be allocated within ZIO segments, see
.IR segment (3),
or data will be copied during I/O. But they can refer to any other segment as well.
.PP
.B Zio
structures passed as an argument represent a series of zero-copy buffers
for the call. For
.I ziowrite
they should refer to actual data. For
.I zioread
the system fills them to reflect where the read data stands. In both cases,
.I nio
is the number of entries in the
.I io
array, and
.I fd
is the file descriptor where to perform I/O. The
.I count
argument to
.I zioread
limits the total ammount of data that may be retrieved.
The return value reflects the number of entries used in the
.I io
array.
.PP
.I Ziopread
and
.I ziopwrite
are similar to
.I zioread
and
.I ziowrite
but specify the offset where to read or write.
.PP
.I ziofree
is a convenience system call to notify buffer owners that they are no longer
in use. Using it is equivalent of locating the
.B free
files for the segments involved and then writing the
.I io
addresses there.
.SH SOURCE
.B /sys/src/libc/9sys/zioread.c
.br
.B /sys/src/libc/9sys/ziowrite.c
.br
.B /sys/src/nix/port/syszio.c
.SH SEE ALSO
.IR intro (2),
.IR read (2),
and
.IR segment (3).
.SH DIAGNOSTICS
These functions set
.IR errstr .
.SH BUGS
Experimental, just like everything else.