READ(5)
NAME
read, write − transfer data from and to a file
SYNOPSIS
Tread tag[2] fid[2] offset[8] count[2]
Rread tag[2] fid[2] count[2] pad[1] data[count]
Twrite tag[2] fid[2] offset[8] count[2] pad[1] data[count]
Rwrite tag[2] fid[2] count[2]
DESCRIPTION
The read request asks for count bytes of data from the file identified by fid, which must be opened for reading, starting offset bytes after the beginning of the file. Count must be less than or equal to MAXFDATA (8192, defined in <styx.h>). The bytes are returned with the read reply message.
The count field in the reply indicates the number of bytes returned. This may be less than the requested amount. If the offset field is greater than the number of bytes in the file, a count of zero will be returned. For directories, read returns an integral number of directory entries exactly as in stat (see stat(5)), one for each member of the directory. The read request message must have offset and count zero modulo DIRLEN (116, defined in <lib9.h>).
The write request asks that count bytes of data be recorded in the file identified by fid, which must be opened for writing, starting offset bytes after the beginning of the file.
Directories may not be written.
The write reply records the number of bytes actually written. It is usually an error if this is not the same as requested.
ENTRY POINTS
Read and write messages are generated by the corresponding calls (see sys-read(2)). Because of the MAXFDATA limit, more than one message may be produced by a single call.
SEE ALSO
Plan 9 — June 29, 2000