lib/scatterlist: mark input buffer parameters as 'const'

The 'buf' parameter of sg(p)copy_from_buffer() can and should be
const-qualified, although because of the shared implementation of
_to_buffer() and _from_buffer(), we have to cast this away internally.

This means that callers who have a 'const' buffer containing the data to
be copied to the sg-list no longer have to cast away the const-ness
themselves.  It also enables improved coverage by code analysis tools.

Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/scatterlist.h

@@ -266,12 +266,12 @@ int sg_alloc_table_from_pages(struct sg_table *sgt,
 	gfp_t gfp_mask);
 
 size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
-			   void *buf, size_t buflen);
+			   const void *buf, size_t buflen);
 size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
 			 void *buf, size_t buflen);
 
 size_t sg_pcopy_from_buffer(struct scatterlist *sgl, unsigned int nents,
-			    void *buf, size_t buflen, off_t skip);
+			    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);
 

lib/scatterlist.c

@@ -701,9 +701,9 @@ static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
  *
  **/
 size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
-			   void *buf, size_t buflen)
+			   const void *buf, size_t buflen)
 {
-	return sg_copy_buffer(sgl, nents, buf, buflen, 0, false);
+	return sg_copy_buffer(sgl, nents, (void *)buf, buflen, 0, false);
 }
 EXPORT_SYMBOL(sg_copy_from_buffer);
 
@@ -736,9 +736,9 @@ EXPORT_SYMBOL(sg_copy_to_buffer);
  *
  **/
 size_t sg_pcopy_from_buffer(struct scatterlist *sgl, unsigned int nents,
-			    void *buf, size_t buflen, off_t skip)
+			    const void *buf, size_t buflen, off_t skip)
 {
-	return sg_copy_buffer(sgl, nents, buf, buflen, skip, false);
+	return sg_copy_buffer(sgl, nents, (void *)buf, buflen, skip, false);
 }
 EXPORT_SYMBOL(sg_pcopy_from_buffer);