.TH READ 5 
.SH NAME
read, write \- transfer data from and to a file
.SH SYNOPSIS
.ta \w'\fLTwrite 'u
.B
Tread	
.IR tag [2]
.IR fid [2]
.IR offset [8]
.IR count [2]
.br
.B
Rread	
.IR tag [2]
.IR fid [2]
.IR count [2]
.IR pad [1]
.IR data [ count ]
.PP
.B
Twrite	
.IR tag [2]
.IR fid [2]
.IR offset [8]
.IR count [2]
.IR pad [1]
.IR data [ count ]
.br
.B
Rwrite	
.IR tag [2]
.IR fid [2]
.IR count [2]
.SH DESCRIPTION
The
.B read
request
asks for
.I count
bytes of data
from the file identified by 
.IR fid ,
which must be opened for reading,
starting 
.I offset
bytes after the beginning of the file.
.I Count
must be less than or equal to
.B MAXFDATA
(8192, defined in
.BR <fcall.h> ).
The bytes are returned with the
.B read
reply message.
.PP
The
.I count
field in the reply indicates the number of bytes returned.
This may be less than the requested amount.
If the
.I offset
field is greater than the number of bytes in the file,
a count of zero will be returned.
For directories,
.B read
returns an integral number of
directory entries exactly as in
.B stat
(see
.IR stat (5)),
one for each member of the directory.
The read request message must have
.B offset
and
.B count
zero modulo
.BR DIRLEN .
.PP
The
.B write
request asks that
.I count
bytes of data be recorded in the file identified by
.IR fid ,
which must be opened for writing, starting
.I offset
bytes after the beginning of the file.
If the file has been opened append only,
the data will be placed at the end of the file regardless of
.IR offset .
Directories may not be written.
.PP
The 
.B write
reply records the number of bytes actually written.
It is usually an error
if this is not the same as requested.
.SH ENTRY POINTS
.B Read
and
.B write
messages are generated by the corresponding calls.
Because of the
.B MAXFDATA
limit, more than one message may be produced by a single
call.