.TH ZP 3 
.SH NAME
zp \- two-way zero-copy interprocess communication
.SH SYNOPSIS
.B bind #∏
.I dir
.nf

.IB dir /data
.IB dir /data1
.fi
.SH DESCRIPTION
.PP
An
.IR attach (5)
of this device allocates two new cross-connected I/O streams,
.IB dir /data
and
.IB dir /data1\f1.
.PP
Data written to one channel becomes available for reading at
the other. Writes are atomic, no matter the size. Writes from
shared buffers, see
.IR segment (3),
queue data descriptors without copying any data. Writes from other
segments copies the data into a kernel ZIO segment.
.PP
Write boundaries are not preserved. A read terminates when the
buffer is full, if the first descriptor queued suffices to fill up the buffer
(in which case remaining data is copied into another shared buffer).
A read also terminates when copying from another descriptor would
overflow the buffer, in which case less bytes than requested may be
returned.
.PP
Writes from non-shared segments
are atomic only up to a certain size, typically 32768 bytes, to
avoid allocation of too large buffers within the kernel.
.PP
If there are multiple writers, each
.I write
is guaranteed to be available in a contiguous piece at the other
end of the pipe.
.PP
The
.IR zp (2)
system call performs an
.I attach
of this device and returns file descriptors to the new pipe's
.B data
and
.B data1
files.
The files are open with mode
.BR ORDWR .
.SH "SEE ALSO"
.IR pipe (3),
.IR pipe (2),
and
.IR zp (2).
.SH SOURCE
.B /sys/src/9/port/devzp.c