xen: provide a prototype for xen_biovec_phys_mergeable in xen.h

Having multiple externs in arch headers is not a good way to provide
a common interface.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

arch/arm/include/asm/io.h

@@ -459,9 +459,6 @@ extern void pci_iounmap(struct pci_dev *dev, void __iomem *addr);
 
 #include <asm-generic/io.h>
 
-struct bio_vec;
-extern bool xen_biovec_phys_mergeable(const struct bio_vec *vec1,
-				      const struct bio_vec *vec2);
 #define ARCH_BIOVEC_PHYS_MERGEABLE(vec1, vec2)				\
 	 (!xen_domain() || xen_biovec_phys_mergeable(vec1, vec2))
 

arch/arm64/include/asm/io.h

@@ -205,9 +205,6 @@ extern int valid_mmap_phys_addr_range(unsigned long pfn, size_t size);
 
 extern int devmem_is_allowed(unsigned long pfn);
 
-struct bio_vec;
-extern bool xen_biovec_phys_mergeable(const struct bio_vec *vec1,
-				      const struct bio_vec *vec2);
 #define ARCH_BIOVEC_PHYS_MERGEABLE(vec1, vec2)				\
 	 (!xen_domain() || xen_biovec_phys_mergeable(vec1, vec2))
 

arch/x86/include/asm/io.h

@@ -371,10 +371,6 @@ extern bool is_early_ioremap_ptep(pte_t *ptep);
 
 #ifdef CONFIG_XEN
 #include <xen/xen.h>
-struct bio_vec;
-
-extern bool xen_biovec_phys_mergeable(const struct bio_vec *vec1,
-				      const struct bio_vec *vec2);
 
 #define ARCH_BIOVEC_PHYS_MERGEABLE(vec1, vec2)				\
 	 (!xen_domain() || xen_biovec_phys_mergeable(vec1, vec2))

include/xen/xen.h

@@ -39,4 +39,8 @@ extern uint32_t xen_start_flags;
 #define xen_initial_domain()	(0)
 #endif	/* CONFIG_XEN_DOM0 */
 
+struct bio_vec;
+bool xen_biovec_phys_mergeable(const struct bio_vec *vec1,
+		const struct bio_vec *vec2);
+
 #endif	/* _XEN_XEN_H */