[PATCH v3 4/4] scatterlist: add sgl_memset()

[Douglas Gilbert]

The existing sg_zero_buffer() function is a bit restrictive.
For example protection information (PI) blocks are usually
initialized to 0xff bytes. As its name suggests sgl_memset()
is modelled on memset(). One difference is the type of the
val argument which is u8 rather than int. Plus it returns
the number of bytes (over)written.

Change implementation of sg_zero_buffer() to call this new
function.

Signed-off-by: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
---
 include/linux/scatterlist.h |  3 ++
 lib/scatterlist.c           | 65 +++++++++++++++++++++++++------------
 2 files changed, 48 insertions(+), 20 deletions(-)

diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index ae260dc5fedb..a40012c8a4e6 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -329,6 +329,9 @@ bool sgl_compare_sgl(struct scatterlist *x_sgl, unsigned int x_nents, off_t x_sk
 		     struct scatterlist *y_sgl, unsigned int y_nents, off_t y_skip,
 		     size_t n_bytes);
 
+size_t sgl_memset(struct scatterlist *sgl, unsigned int nents, off_t skip,
+		  u8 val, size_t n_bytes);
+
 /*
  * Maximum number of entries that will be allocated in one piece, if
  * a list larger than this is required then chaining will be utilized.
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 49185536acba..6b430f7293e0 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -952,26 +952,7 @@ EXPORT_SYMBOL(sg_pcopy_to_buffer);
 size_t sg_zero_buffer(struct scatterlist *sgl, unsigned int nents,
 		       size_t buflen, off_t skip)
 {
-	unsigned int offset = 0;
-	struct sg_mapping_iter miter;
-	unsigned int sg_flags = SG_MITER_ATOMIC | SG_MITER_TO_SG;
-
-	sg_miter_start(&miter, sgl, nents, sg_flags);
-
-	if (!sg_miter_skip(&miter, skip))
-		return false;
-
-	while (offset < buflen && sg_miter_next(&miter)) {
-		unsigned int len;
-
-		len = min(miter.length, buflen - offset);
-		memset(miter.addr, 0, len);
-
-		offset += len;
-	}
-
-	sg_miter_stop(&miter);
-	return offset;
+	return sgl_memset(sgl, nents, skip, 0, buflen);
 }
 EXPORT_SYMBOL(sg_zero_buffer);
 
@@ -1110,3 +1091,47 @@ bool sgl_compare_sgl(struct scatterlist *x_sgl, unsigned int x_nents, off_t x_sk
 	return equ;
 }
 EXPORT_SYMBOL(sgl_compare_sgl);
+
+/**
+ * sgl_memset - set byte 'val' up to n_bytes times on SG list
+ * @sgl:		 The SG list
+ * @nents:		 Number of SG entries in sgl
+ * @skip:		 Number of bytes to skip before starting
+ * @val:		 byte value to write to sgl
+ * @n_bytes:		 The (maximum) number of bytes to modify
+ *
+ * Returns:
+ *   The number of bytes written.
+ *
+ * Notes:
+ *   Stops writing if either sgl or n_bytes is exhausted. If n_bytes is
+ *   set SIZE_MAX then val will be written to each byte until the end
+ *   of sgl.
+ *
+ *   The notes in sgl_copy_sgl() about large sgl_s _applies here as well.
+ *
+ **/
+size_t sgl_memset(struct scatterlist *sgl, unsigned int nents, off_t skip,
+		  u8 val, size_t n_bytes)
+{
+	size_t offset = 0;
+	size_t len;
+	struct sg_mapping_iter miter;
+
+	if (n_bytes == 0)
+		return 0;
+	sg_miter_start(&miter, sgl, nents, SG_MITER_ATOMIC | SG_MITER_TO_SG);
+	if (!sg_miter_skip(&miter, skip))
+		goto fini;
+
+	while ((offset < n_bytes) && sg_miter_next(&miter)) {
+		len = min(miter.length, n_bytes - offset);
+		memset(miter.addr, val, len);
+		offset += len;
+	}
+fini:
+	sg_miter_stop(&miter);
+	return offset;
+}
+EXPORT_SYMBOL(sgl_memset);
+
-- 
2.25.1