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

[Douglas Gilbert <dgilbert@interlog.com>]

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.

Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
---
 include/linux/scatterlist.h |  3 +++
 lib/scatterlist.c           | 39 +++++++++++++++++++++++++++++++++++--
 2 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index ae260dc5fedb..e50dc9a6d887 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);
 
+void 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 344725990b9d..3ca66f0c949f 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -1083,8 +1083,8 @@ EXPORT_SYMBOL(sgl_copy_sgl);
  *
  **/
 bool sgl_compare_sgl(struct scatterlist *x_sgl, unsigned int x_nents, off_t x_skip,
-		     struct scatterlist *y_sgl, unsigned int y_nents, off_t y_skip,
-		     size_t n_bytes)
+		    struct scatterlist *y_sgl, unsigned int y_nents, off_t y_skip,
+		    size_t n_bytes)
 {
 	bool equ = true;
 	size_t x_off, y_off, len, x_len, y_len;
@@ -1140,3 +1140,38 @@ 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' 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 number of bytes to modify
+ *
+ * Notes:
+ *   Writes val n_bytes times or until sgl is exhausted.
+ *
+ **/
+void 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;
+	unsigned int sg_flags = SG_MITER_ATOMIC | SG_MITER_TO_SG;
+
+	if (n_bytes == 0)
+		return;
+	sg_miter_start(&miter, sgl, nents, sg_flags);
+	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);
+}
-- 
2.25.1