fix region offset handling (#485)

The specification states that the region offset given in the region info should
be used as the "offset" when mmap()ing the region from the client side. However,
the library instead implemented a fixed offset scheme  similar to that of vfio -
and no clients actually set up the file like that.

Instead, let servers define their own offsets, and pass them through to clients
as is. It's up to the server to decide how its backing file or files is
organized.

Signed-off-by: John Levon <john.levon@nutanix.com>
Reviewed-by: Thanos Makatos <thanos.makatos@nutanix.com>

1 files changed, 2 insertions, 11 deletions

diff --git a/include/libvfio-user.h b/include/libvfio-user.h
index 371daaf..6cb817d 100644
--- a/include/libvfio-user.h
+++ b/include/libvfio-user.h
@@ -292,6 +292,7 @@ typedef ssize_t (vfu_region_access_cb_t)(vfu_ctx_t *vfu_ctx, char *buf,
  * @fd: file descriptor of the file backing the region if the region is
  *  mappable; it is the server's responsibility to create a file suitable for
  *  memory mapping by the client.
+ * @offset: offset of the region within the fd, or zero.
  *
  * @returns 0 on success, -1 on error, Sets errno.
  */
@@ -299,7 +300,7 @@ int
 vfu_setup_region(vfu_ctx_t *vfu_ctx, int region_idx, size_t size,
                  vfu_region_access_cb_t *region_access, int flags,
                  struct iovec *mmap_areas, uint32_t nr_mmap_areas,
-                 int fd);
+                 int fd, uint64_t offset);
 
 /*
  * Returns the size of the area needed to hold the migration registers at the
@@ -857,16 +858,6 @@ size_t
 vfu_pci_find_next_capability(vfu_ctx_t *vfu_ctx, bool extended,
                              size_t pos, int cap_id);
 
-/**
- * Returns the memory offset where the specific region starts in device memory.
- *
- * @region: the region to translate
- *
- * @returns the absolute offset
- */
-uint64_t
-vfu_region_to_offset(uint32_t region);
-
 #ifdef __cplusplus
 }
 #endif