READ(5) File Formats Manual READ(5)
read, write - transfer data from and to a file
Tread tag fid offset count
Rread tag fid count pad data[count]
Twrite tag fid offset count pad data[count]
Rwrite tag fid count
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 MAXF-
DATA (8192, defined in <<fcall.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 direc-
tory 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
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 offset. 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.
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.