kmap_sg() is basically scsi_kmap_atomic_sg() but uses kmap_local()
and does not enforce disabled interrupts.
Signed-off-by: Richard Weinberger <richard@xxxxxx>
---
include/linux/scatterlist.h | 3 ++
lib/scatterlist.c | 55 +++++++++++++++++++++++++++++++++++++
2 files changed, 58 insertions(+)
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 77df3d7b18a61..dd25a87609491 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -692,4 +692,7 @@ bool sg_miter_skip(struct sg_mapping_iter *miter, off_t offset);
bool sg_miter_next(struct sg_mapping_iter *miter);
void sg_miter_stop(struct sg_mapping_iter *miter);
+void *kmap_sg(struct scatterlist *sgl, int sg_count, size_t *offset, size_t *len);
+void kunmap_sg(void *virt);
+
#endif /* _LINUX_SCATTERLIST_H */
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index e86231a44c3de..7428d9461711d 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -1364,3 +1364,58 @@ ssize_t extract_iter_to_sg(struct iov_iter *iter, size_t maxsize,
}
}
EXPORT_SYMBOL_GPL(extract_iter_to_sg);
+
+/**
+ * kmap_sg - find and kmap an sg-elemnt
+ * @sgl: scatter-gather list
+ * @sg_count: number of segments in sg
+ * @offset: offset in bytes into sg, on return offset into the mapped area
+ * @len: bytes to map, on return number of bytes mapped
+ *
+ * Returns virtual address of the start of the mapped page
+ */
+void *kmap_sg(struct scatterlist *sgl, int sg_count, size_t *offset, size_t *len)
+{
+ int i;
+ size_t sg_len = 0, len_complete = 0;
+ struct scatterlist *sg;
+ struct page *page;
+
+ for_each_sg(sgl, sg, sg_count, i) {
+ len_complete = sg_len; /* Complete sg-entries */
+ sg_len += sg->length;
+ if (sg_len > *offset)
+ break;
+ }
+
+ if (WARN_ON_ONCE(i == sg_count)) {
+ pr_err("%s: Bytes in sg: %zu, requested offset %zu, elements %d\n",
+ __func__, sg_len, *offset, sg_count);
+ return NULL;
+ }
+
+ /* Offset starting from the beginning of first page in this sg-entry */
+ *offset = *offset - len_complete + sg->offset;
+
+ /* Assumption: contiguous pages can be accessed as "page + i" */
+ page = nth_page(sg_page(sg), (*offset >> PAGE_SHIFT));
+ *offset &= ~PAGE_MASK;
+
+ /* Bytes in this sg-entry from *offset to the end of the page */
+ sg_len = PAGE_SIZE - *offset;
+ if (*len > sg_len)
+ *len = sg_len;
+
+ return kmap_local_page(page);
+}
+EXPORT_SYMBOL(kmap_sg);
+
+/**
+ * kunmap_sg - atomically unmap a virtual address, previously mapped with kmap_sg
+ * @virt: virtual address to be unmapped
+ */
+void kunmap_sg(void *virt)
+{
+ kunmap_local(virt);
+}
+EXPORT_SYMBOL(kunmap_sg);
--
2.35.3
