xen/grant: Introduce helpers to split a page into grant

Currently, a grant is always based on the Xen page granularity (i.e
4KB). When Linux is using a different page granularity, a single page
will be split between multiple grants.

The new helpers will be in charge of splitting the Linux page into grants
and call a function given by the caller on each grant.

Also provide an helper to count the number of grants within a given
contiguous region.

Note that the x86/include/asm/xen/page.h is now including
xen/interface/grant_table.h rather than xen/grant_table.h. It's
necessary because xen/grant_table.h depends on asm/xen/page.h and will
break the compilation. Furthermore, only definition in
interface/grant_table.h is required.

Signed-off-by: Julien Grall <julien.grall@citrix.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

1 files changed, 26 insertions, 0 deletions

diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index a4b702c9ac68..dbeaa67dec47 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -776,6 +776,32 @@ void gnttab_batch_copy(struct gnttab_copy *batch, unsigned count)
 }
 EXPORT_SYMBOL_GPL(gnttab_batch_copy);
 
+void gnttab_foreach_grant_in_range(struct page *page,
+                                   unsigned int offset,
+                                   unsigned int len,
+                                   xen_grant_fn_t fn,
+                                   void *data)
+{
+        unsigned int goffset;
+        unsigned int glen;
+        unsigned long xen_pfn;
+
+        len = min_t(unsigned int, PAGE_SIZE - offset, len);
+        goffset = xen_offset_in_page(offset);
+
+        xen_pfn = page_to_xen_pfn(page) + XEN_PFN_DOWN(offset);
+
+        while (len) {
+                glen = min_t(unsigned int, XEN_PAGE_SIZE - goffset, len);
+                fn(pfn_to_gfn(xen_pfn), goffset, glen, data);
+
+                goffset = 0;
+                xen_pfn++;
+                len -= glen;
+        }
+}
+EXPORT_SYMBOL_GPL(gnttab_foreach_grant_in_range);
+
 int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
                     struct gnttab_map_grant_ref *kmap_ops,
                     struct page **pages, unsigned int count)