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Re: [Xen-devel] [PATCH] Cleanup rmb()/wmb() usage

Keir Fraser wrote:

On 23 Feb 2005, at 03:38, Anthony Liguori wrote:

asm/system.h is a private kernel header so should not be directly included from user space. Inlcuding it may not work for all versions of Linux, or for other architectures.

Actually, asm/system.h is designed for inclusion in userspace apps (and kernel space). Hence the __KERNEL__ guards around certain sections.

It's used in a few notable userspace apps including glibc and MySQL. That said, Xen should not depend on Linux if it doesn't have to.

We should probably merge the barrier defs we have scattered in the tools directory into one low-level architectural header that we include everywhere, and extend for x86/64, ia64, and so on.

Agreed. Any ideas on where it would live? I didn't see any likely place which is why I used asm/system. io/ring.h seemed the closest fit but that's not architecture specific.

Only Centaur clones that have been set up by the kernel to do write combining. Xen does not ever enable write-combining on normal RAM and so a barrier is never required.

Ah, that makes sense. It still would be nice to have the barriers in a single location. Pick a place and I'll submit a patch.


Anthony Liguori

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