Messages in this thread | | | Date | Thu, 4 Sep 2003 21:04:26 +0100 | From | Jamie Lokier <> | Subject | Re: [PATCH] Alternate futex non-page-pinning and COW fix |
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Linus Torvalds wrote: > > * I contend that the user-visible behaviour of a mapping should > > * _not_ depend on whether the file was opened with O_RDWR or O_RDONLY. > > And I violently agree. But I also add the _other_ requirement: > > * I contend that user-visible behaviour of a mapping should be 100% the > * same for a unwritable MAP_SHARED and a unwritten MAP_PRIVATE > > Put the two together, and see what you get. You get the requirement that > if MAP_SHARED works, then MAP_PRIVATE also has to work.
I'll add three more conditions to be explicit:
* A futex on a MAP_PRIVATE must be mm-local: the canonical * example being MAP_PRIVATE of /dev/zero.
* A FUTEX_WAIT on an unwritten mapping should be woken by a * FUTEX_WAKE to the same address after writing.
* A FUTEX_WAIT on a read-only mapping should wait for the same * thing from other processes as if it were a writable mapping.
> That's my requirement. Consistency.
Unfortunately I think the above 5 conditions do not have a consistent solution. Please prove me wrong :)
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