[PATCH v5 1/9] scatterlist: add sg_zeroout_area() helper

From: Johannes Thumshirn
Date: Tue Jun 06 2017 - 10:37:18 EST


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

Signed-off-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
---
include/linux/scatterlist.h | 3 +++
lib/scatterlist.c | 37 +++++++++++++++++++++++++++++++++++++
2 files changed, 40 insertions(+)

diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index cb3c8fe6acd7..a38ce9f4e78a 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -279,6 +279,9 @@ size_t sg_pcopy_from_buffer(struct scatterlist *sgl, unsigned int nents,
size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents,
void *buf, size_t buflen, off_t skip);

+size_t sg_zeroout_area(struct scatterlist *sgl, unsigned int nents,
+ size_t buflen, off_t skip);
+
/*
* 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 c6cf82242d65..ce311cde2654 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -751,3 +751,40 @@ size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents,
return sg_copy_buffer(sgl, nents, buf, buflen, skip, true);
}
EXPORT_SYMBOL(sg_pcopy_to_buffer);
+
+/**
+ * sg_zeroout_area - Zero-out a part of a SG list
+ * @sgl: The SG list
+ * @nents: Number of SG entries
+ * @buflen: The number of bytes to zero out
+ * @skip: Number of bytes to skip before zeroing
+ *
+ * Returns the number of bytes zeroed.
+ *
+ **/
+size_t sg_zeroout_area(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;
+}
+EXPORT_SYMBOL(sg_zeroout_area);
--
2.12.3