SYS$QIO (OpenVMS) SYS$QIO (OpenVMS)
NAME
read - read from a file
write - write to a file
select - synchronous I/O multiplexing
SYS$QIO - Queue I/O request
SYS$QIOW - Queue I/O request and wait
EXPLAINATION
The Digital UNIX read, write, and select system calls provide functionâ
ality similar to the OpenVMS SYS$QIO and SYS$QIOW system service. The
read system call reads from the object described the descriptor and
puts the information read into the provided buffer until the maximum
number of bytes is read or an error occurs. The write system call
writes the specified number of bytes from the buffer to the objected
described by the descriptor. It is important to realize that the read
and write calls are synchronous, control is not passed back to the
process until the operation is complete. However, with slow block
devices, the buffer cache is generally employed, resulting in increased
I/O times. It is possible to use fcntl to change a descriptor to a
nonblocking descriptor. Nonblocking reads and writes return as soon as
the operation would block. The number of bytes written or read is
returned. It is also possible to use the select system call to obtain
a set of descriptors for which I/O is possible and then read or write
to those descriptors.
RELATED INFORMATION
Digital UNIX Functions:
select(2), read(2), write(2), open(2), close(2), fcntl(2) delim off
SYS$QIO (OpenVMS)
