Re: O_CAREFUL flag to disable open() side effects

From: H. Peter Anvin
Date: Thu Jul 27 2006 - 14:02:01 EST

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.


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