lib/scatterlist: export sg_miter_skip()

sg_copy_buffer() can't meet demand for some drrivers(such usb
mass storage), so we have to use the sg_miter_* APIs to access
sg buffer, then need export sg_miter_skip() for these drivers.

The API is needed for converting to sg_miter_* APIs in USB storage
driver for accessing sg buffer.

Acked-by: Andrew Morton <[e-mail]>
Cc: FUJITA Tomonori <[e-mail]>
Cc: Jens Axboe <[e-mail]>
Signed-off-by: Ming Lei <[e-mail]>
Reviewed-by: Tejun Heo <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

include/linux/scatterlist.h

···
 
 void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
 		    unsigned int nents, unsigned int flags);
+bool sg_miter_skip(struct sg_mapping_iter *miter, off_t offset);
 bool sg_miter_next(struct sg_mapping_iter *miter);
 void sg_miter_stop(struct sg_mapping_iter *miter);
 

lib/scatterlist.c

···
  *   true if @miter contains the valid mapping.  false if end of sg
  *   list is reached.
  */
-static bool sg_miter_skip(struct sg_mapping_iter *miter, off_t offset)
+bool sg_miter_skip(struct sg_mapping_iter *miter, off_t offset)
 {
 	sg_miter_stop(miter);
 
···
 
 	return true;
 }
+EXPORT_SYMBOL(sg_miter_skip);
 
 /**
  * sg_miter_next - proceed mapping iterator to the next mapping