After enabling copies between scatter gather lists (sgl_s),
another storage related operation is to compare two sgl_s.
This new function is modelled on NVMe's Compare command and
the SCSI VERIFY(BYTCHK=1) command. Like memcmp() this function
returns false on the first miscompare and stop comparing.
Signed-off-by: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
---
include/linux/scatterlist.h | 4 ++
lib/scatterlist.c | 84 ++++++++++++++++++++++++++++++++++++-
2 files changed, 86 insertions(+), 2 deletions(-)
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 6649414c0749..ae260dc5fedb 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -325,6 +325,10 @@ size_t sgl_copy_sgl(struct scatterlist *d_sgl, unsigned int d_nents, off_t d_ski
struct scatterlist *s_sgl, unsigned int s_nents, off_t s_skip,
size_t n_bytes);
+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);
+
/*
* 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 1ec2c909c8d4..344725990b9d 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -979,10 +979,10 @@ EXPORT_SYMBOL(sg_zero_buffer);
* sgl_copy_sgl - Copy over a destination sgl from a source sgl
* @d_sgl: Destination sgl
* @d_nents: Number of SG entries in destination sgl
- * @d_skip: Number of bytes to skip in destination before copying
+ * @d_skip: Number of bytes to skip in destination before starting
* @s_sgl: Source sgl
* @s_nents: Number of SG entries in source sgl
- * @s_skip: Number of bytes to skip in source before copying
+ * @s_skip: Number of bytes to skip in source before starting
* @n_bytes: The number of bytes to copy
*
* Returns the number of copied bytes.
@@ -1060,3 +1060,83 @@ size_t sgl_copy_sgl(struct scatterlist *d_sgl, unsigned int d_nents, off_t d_ski
}
EXPORT_SYMBOL(sgl_copy_sgl);
+/**
+ * sgl_compare_sgl - Compare x and y (both sgl_s)
+ * @x_sgl: x (left) sgl
+ * @x_nents: Number of SG entries in x (left) sgl
+ * @x_skip: Number of bytes to skip in x (left) before starting
+ * @y_sgl: y (right) sgl
+ * @y_nents: Number of SG entries in y (right) sgl
+ * @y_skip: Number of bytes to skip in y (right) before starting
+ * @n_bytes: The number of bytes to compare
+ *
+ * Returns true if x and y compare equal before x, y or n_bytes is exhausted.
+ * Otherwise on a miscompare, returns false (and stops comparing).
+ *
+ * Notes:
+ * x and y are symmetrical: they can be swapped and the result is the same.
+ *
+ * Implementation is based on memcmp(). x and y segments may overlap.
+ *
+ * Same comment from sgl_copy_sgl() about large _skip arguments applies here
+ * as well.
+ *
+ **/
+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)
+{
+ bool equ = true;
+ size_t x_off, y_off, len, x_len, y_len;
+ size_t offset = 0;
+ struct sg_mapping_iter x_iter;
+ struct sg_mapping_iter y_iter;
+
+ if (n_bytes == 0)
+ return true;
+ sg_miter_start(&x_iter, x_sgl, x_nents, SG_MITER_ATOMIC | SG_MITER_TO_SG);
+ sg_miter_start(&y_iter, y_sgl, y_nents, SG_MITER_ATOMIC | SG_MITER_FROM_SG);
+ if (!sg_miter_skip(&x_iter, x_skip))
+ goto fini;
+ if (!sg_miter_skip(&y_iter, y_skip))
+ goto fini;
+
+ for (x_off = 0, y_off = 0; true ; ) {
+ /* Assume x_iter.length and y_iter.length can never be 0 */
+ if (x_off == 0) {
+ if (!sg_miter_next(&x_iter))
+ break;
+ x_len = x_iter.length;
+ } else {
+ x_len = x_iter.length - x_off;
+ }
+ if (y_off == 0) {
+ if (!sg_miter_next(&y_iter))
+ break;
+ y_len = y_iter.length;
+ } else {
+ y_len = y_iter.length - y_off;
+ }
+ len = min3(x_len, y_len, n_bytes - offset);
+
+ equ = memcmp(x_iter.addr + x_off, y_iter.addr + y_off, len) == 0;
+ offset += len;
+ if (!equ || offset >= n_bytes)
+ break;
+ if (x_len == y_len) {
+ x_off = 0;
+ y_off = 0;
+ } else if (x_len < y_len) {
+ x_off = 0;
+ y_off += len;
+ } else {
+ x_off += len;
+ y_off = 0;
+ }
+ }
+fini:
+ sg_miter_stop(&x_iter);
+ sg_miter_stop(&y_iter);
+ return equ;
+}
+EXPORT_SYMBOL(sgl_compare_sgl);
--
2.25.1
