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Diffstat (limited to 'unix/os/doc/zzrdmt.hlp')
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diff --git a/unix/os/doc/zzrdmt.hlp b/unix/os/doc/zzrdmt.hlp new file mode 100644 index 00000000..aea7cf74 --- /dev/null +++ b/unix/os/doc/zzrdmt.hlp @@ -0,0 +1,37 @@ +.help zzrdmt May84 "System Interface" +.ih +NAME +zzrdmt -- asynchronous read from a magtape file +.ih +SYNOPSIS +.nf +zzrdmt (chan, buf, maxbytes) + +int chan # OS channel of magtape file +char buf[maxbytes] # output buffer to receive data +int maxbytes # capacity of buffer +.fi +.ih +DESCRIPTION +Initiate a read of at most \fImaxbytes\fR bytes from channel \fIchan\fR into +the buffer \fIbuf\fR. If the physical file block is larger than \fImaxbytes\fR +bytes the additional data will be discarded. Each call to \fBzzrdmt\fR reads +one tape block. Successive tape blocks may vary in size. +.ih +RETURN VALUE +The wait primitive \fBzzwtmt\fR must be called after every asynchronous read +to get the transfer status. ERR is returned if a read error occurs or if the +channel number is illegal. If the read operation is successful the actual +number of bytes read is returned; zero is returned for a read at EOF. +.ih +NOTES +The transfer is NOT guaranteed to be asynchronous and the calling program +must not assume that \fBzzrdmt\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. A request to read zero bytes is considered +to be an error to avoid confusion with a read at EOF. +.ih +SEE ALSO +zzopmt, zzwtmt, zfiomt +.endhelp |