.help zzwrmt May84 "System Interface"
.ih
NAME
zzwrmt -- asynchronous write to a magtape file
.ih
SYNOPSIS
.nf
zzwrmt (chan, buf, nbytes)

int	chan			# OS channel of magtape file
char	buf[nbytes]		# buffer containing the data
int	nbytes			# number of bytes to be written
.fi
.ih
DESCRIPTION
Initiate a write of exactly \fInbytes\fR bytes from the buffer \fIbuf\fR to
the magtape channel \fIchan\fR.  Each call to \fBzzwrmt\fR writes one tape
block.  Successive tape blocks may vary in size.  A request to write zero
bytes is ignored.
.ih
RETURN VALUE
The wait primitive \fBzzwtmt\fR must be called after every asynchronous write
to get the transfer status.  ERR is returned if a write error occurs or if the
channel number is illegal.  If the write operation is successful the actual
number of bytes written is returned.
.ih
NOTES
The transfer is NOT guaranteed to be asynchronous and the calling program
must not assume that \fBzzwrmt\fR will return immediately.
The \fBzzwtmt\fR primitive must be called and the status checked before
issuing another i/o request to the channel.  Only a single request may be
pending on a channel at a time.
.ih
SEE ALSO
zzopmt, zzwtmt, zfiomt
.endhelp