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Subject[PATCH v5 4/4] scatterlist: add sgl_memset()
Date
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@gmail.com>
Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
---
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 71be65f9ebb5..70d3f1f73df1 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -333,6 +333,9 @@ 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
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