Re: O_CAREFUL flag to disable open() side effects

From: Russell King
Date: Thu Jul 27 2006 - 13:41:22 EST

On Thu, Jul 27, 2006 at 10:33:23AM -0700, H. Peter Anvin wrote:
> Dumb thought: would it make sense to add an O_CAREFUL flag to open(), to
> disable side effects? It seems that a number of devices have this issue
> and one have to jump through weird hoops to configure them. Obviously,
> a file descriptor obtained with O_CAREFUL may not be fully functional,
> at the device driver's option.
> For a conventional file, directory, or block device O_CAREFUL is a
> no-op.

What about door locking on block devices? That might be an undesirable
side effect in some circumstances, so you might not want it to be a no-op
on blockdevs.

> For ttys it would typically behave similar to O_NONBLOCK
> followed immediately by a fcntl to clear the nonblock flag.

What about, eg, raising DTR and RTS ? You'd want to avoid raising
those if you're not actually going to be using the port.

Russell King
Linux kernel 2.6 ARM Linux -
maintainer of: 2.6 Serial core
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