[PATCH] allow arch override of BIOVEC_PHYS_MERGEABLE

This patch is from the Xen crew - it allows override of deciding whether
two given pages can be considered physically contigous or not. This is
similar to how we handle iommu and virtual merging.
Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/bio.h

@@ -188,8 +188,15 @@ struct bio {
 
 #define __BVEC_END(bio)		bio_iovec_idx((bio), (bio)->bi_vcnt - 1)
 #define __BVEC_START(bio)	bio_iovec_idx((bio), (bio)->bi_idx)
+
+/*
+ * allow arch override, for eg virtualized architectures (put in asm/io.h)
+ */
+#ifndef BIOVEC_PHYS_MERGEABLE
 #define BIOVEC_PHYS_MERGEABLE(vec1, vec2)	\
 	((bvec_to_phys((vec1)) + (vec1)->bv_len) == bvec_to_phys((vec2)))
+#endif
+
 #define BIOVEC_VIRT_MERGEABLE(vec1, vec2)	\
 	((((bvec_to_phys((vec1)) + (vec1)->bv_len) | bvec_to_phys((vec2))) & (BIO_VMERGE_BOUNDARY - 1)) == 0)
 #define __BIO_SEG_BOUNDARY(addr1, addr2, mask) \