xen/grants: support allocating consecutive grants

For support of virtio via grant mappings in rare cases larger mappings
using consecutive grants are needed. Support those by adding a bitmap
of free grants.

As consecutive grants will be needed only in very rare cases (e.g. when
configuring a virtio device with a multi-page ring), optimize for the
normal case of non-consecutive allocations.
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/1654197833-25362-3-git-send-email-olekstysh@gmail.comSigned-off-by: Juergen Gross <jgross@suse.com>

include/xen/grant_table.h

@@ -127,10 +127,14 @@ int gnttab_try_end_foreign_access(grant_ref_t ref);
  */
 int gnttab_alloc_grant_references(u16 count, grant_ref_t *pprivate_head);
 
+int gnttab_alloc_grant_reference_seq(unsigned int count, grant_ref_t *first);
+
 void gnttab_free_grant_reference(grant_ref_t ref);
 
 void gnttab_free_grant_references(grant_ref_t head);
 
+void gnttab_free_grant_reference_seq(grant_ref_t head, unsigned int count);
+
 int gnttab_empty_grant_references(const grant_ref_t *pprivate_head);
 
 int gnttab_claim_grant_reference(grant_ref_t *pprivate_head);