Re: [RFD w/info-PATCH] device arguments from lookup, partion code

Alexander Viro
2001-05-20T02:32:28Z

On Sat, 19 May 2001, Richard Gooch wrote:

> There is another reason to use ioctl(2): when you need to send data to
> the kernel/driver and wait for a response. It supports transactions,
> which read(2) and write(2) cannot. Therefore it remains useful.

Somebody, run to database vendors and tell them that they were selling
snake oil all that time - Richard had just shown that support of remote
transactions is impossible. Can't do that with read() and write(),
dontcha know?

Richard, I hate to break it on you, but
fd = open(foo, 2);
/* kernel creates a new struct file, as usual */
write(fd, data, len);
/* kernel starts the operation */
read(fd, reply, size);
/* we block */
/* operation is completed */
/* kernel passes reply to user and wakes it up */
_is_ a support of transactions. And yes, we can trivially distinguish
between requests from different sources - struct file * passed to
->write() is more than enough for that. Moreover, we can easily block
other writers until the action is completed.

Please, get a bloody clue. There are reasons for and against ioctls, but
need to send data and wait for responce is _NOT_ one of them.