scatterlist: add sg_zero_buffer() helper

The sg_zero_buffer() helper is used to zero fill an area in a SG
list.

Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
[hch: renamed to sg_zero_buffer]
Signed-off-by: Christoph Hellwig <hch@lst.de>
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index cb3c8fe..4b3286a 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -278,6 +278,8 @@ size_t sg_pcopy_from_buffer(struct scatterlist *sgl, unsigned int nents,
 			    const void *buf, size_t buflen, off_t skip);
 size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents,
 			  void *buf, size_t buflen, off_t skip);
+size_t sg_zero_buffer(struct scatterlist *sgl, unsigned int nents,
+		       size_t buflen, off_t skip);
 
 /*
  * Maximum number of entries that will be allocated in one piece, if