Both the SCSI and NVMe subsystems receive user data from the block
layer in scatterlist_s (aka scatter gather lists (sgl) which are
often arrays). If drivers in those subsystems represent storage
(e.g. a ramdisk) or cache "hot" user data then they may also
choose to use scatterlist_s. Currently there are no sgl to sgl
operations in the kernel. Start with a copy.
Signed-off-by: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
---
include/linux/scatterlist.h | 4 ++
lib/scatterlist.c | 86 +++++++++++++++++++++++++++++++++++++
2 files changed, 90 insertions(+)
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 80178afc2a4a..6649414c0749 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -321,6 +321,10 @@ size_t sg_pcopy_to_buffer(struct scatterlist *sgl,
unsigned int nents,
size_t sg_zero_buffer(struct scatterlist *sgl, unsigned int nents,
size_t buflen, off_t skip);
+size_t sgl_copy_sgl(struct scatterlist *d_sgl, unsigned int d_nents, off_t
d_skip,
+ struct scatterlist *s_sgl, unsigned int s_nents, off_t s_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 d5770e7f1030..1ec2c909c8d4 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -974,3 +974,89 @@ size_t sg_zero_buffer(struct scatterlist *sgl, unsigned
int nents,
return offset;
}
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
+ * @s_sgl: Source sgl
+ * @s_nents: Number of SG entries in source sgl
+ * @s_skip: Number of bytes to skip in source before copying
+ * @n_bytes: The number of bytes to copy
+ *
+ * Returns the number of copied bytes.
+ *
+ * Notes:
+ * Destination arguments appear before the source arguments, as with memcpy().
+ *
+ * Stops copying if the end of d_sgl or s_sgl is reached.
+ *
+ * Since memcpy() is used, overlapping copies (where d_sgl and s_sgl belong
+ * to the same sgl and the copy regions overlap) are not supported.
+ *
+ * If d_skip is large, potentially spanning multiple d_nents then some
+ * integer arithmetic to adjust d_sgl may improve performance. For example
+ * if d_sgl is built using sgl_alloc_order(chainable=false) then the sgl
+ * will be an array with equally sized segments facilitating that
+ * arithmetic. The suggestion applies to s_skip, s_sgl and s_nents as well.
+ *
+ **/
+size_t sgl_copy_sgl(struct scatterlist *d_sgl, unsigned int d_nents, off_t
d_skip,
+ struct scatterlist *s_sgl, unsigned int s_nents, off_t s_skip,
+ size_t n_bytes)
+{
+ size_t d_off, s_off, len, d_len, s_len;
+ size_t offset = 0;
+ struct sg_mapping_iter d_iter;
+ struct sg_mapping_iter s_iter;
+
+ if (n_bytes == 0)
+ return 0;
+ sg_miter_start(&d_iter, d_sgl, d_nents, SG_MITER_ATOMIC | SG_MITER_TO_SG);
+ sg_miter_start(&s_iter, s_sgl, s_nents, SG_MITER_ATOMIC | SG_MITER_FROM_SG);
+ if (!sg_miter_skip(&d_iter, d_skip))
+ goto fini;
+ if (!sg_miter_skip(&s_iter, s_skip))
+ goto fini;
+
+ for (d_off = 0, s_off = 0; true ; ) {
+ /* Assume d_iter.length and s_iter.length can never be 0 */
+ if (d_off == 0) {
+ if (!sg_miter_next(&d_iter))
+ break;
+ d_len = d_iter.length;
+ } else {
+ d_len = d_iter.length - d_off;
+ }
+ if (s_off == 0) {
+ if (!sg_miter_next(&s_iter))
+ break;
+ s_len = s_iter.length;
+ } else {
+ s_len = s_iter.length - s_off;
+ }
+ len = min3(d_len, s_len, n_bytes - offset);
+
+ memcpy(d_iter.addr + d_off, s_iter.addr + s_off, len);
+ offset += len;
+ if (offset >= n_bytes)
+ break;
+ if (d_len == s_len) {
+ d_off = 0;
+ s_off = 0;
+ } else if (d_len < s_len) {
+ d_off = 0;
+ s_off += len;
+ } else {
+ d_off += len;
+ s_off = 0;
+ }
+ }
+fini:
+ sg_miter_stop(&d_iter);
+ sg_miter_stop(&s_iter);
+ return offset;
+}
+EXPORT_SYMBOL(sgl_copy_sgl);
+
