[PATCH v4 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.

Reviewed-by: Bodo Stroesser <bostroesser@xxxxxxxxx>
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 0f6d59bf66cb..8e4c050e6237 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -339,6 +339,9 @@ bool sgl_compare_sgl_idx(struct scatterlist *x_sgl, unsigned int x_nents, off_t
 			 struct scatterlist *y_sgl, unsigned int y_nents, off_t y_skip,
 			 size_t n_bytes, size_t *miscompare_idx);
 
+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 9332365e7eb6..f06614a880c8 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -1038,26 +1038,7 @@ 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);
 
@@ -1243,3 +1224,47 @@ bool sgl_compare_sgl(struct scatterlist *x_sgl, unsigned int x_nents, off_t x_sk
 	return sgl_compare_sgl_idx(x_sgl, x_nents, x_skip, y_sgl, y_nents, y_skip, n_bytes, NULL);
 }
 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