READ(5) 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, start-
ing offset bytes after the beginning of the file. Count
must be less than or equal to MAXFDATA (8192, defined in
<fcall.h>). The bytes are returned with the read reply mes-
sage.
The count field in the reply indicates the number of charac-
ters returned. This may be less than the requested amount.
If the offset field is greater than the number of characters
in the file, a count of zero will be returned. For directo-
ries, 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.
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 characters 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 offset.
Directories may not be written.
The write reply records the number of characters 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. Because of the MAXFDATA limit, more than one message
may be produced by a single call.
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