Re: O_CAREFUL flag to disable open() side effects

["H. Peter Anvin" <hpa@zytor.com>]

Alan Cox wrote:
> Ar Iau, 2006-07-27 am 10:33 -0700, ysgrifennodd H. Peter Anvin:
>> For a conventional file, directory, or block device O_CAREFUL is a 
>> no-op.  For ttys it would typically behave similar to O_NONBLOCK 
>> followed immediately by a fcntl to clear the nonblock flag.
> 
> Linus long ago suggested O_NONE to go with RO/RW/WO. Its not that hard
> to do with the current file op stuff but you have to work out what the
> access permission semantics of it are and what it means for ioctl etc

O_NONE might be a good thing to do with that, but I think the "careful" 
semantics should be a separate flag (we shouldn't have different side 
effects depending on the individual mode.)

O_NONE would be a useful complement to O_CAREFUL though; for some 
devices O_CAREFUL with anything *other than* O_NONE might be an invalid 
operation.

The semantics would obviously be device dependent, but the basic idea 
should be that opening with O_CAREFUL should not disturb the global 
state of the device; it should only create a handle.

	-hpa