iov_iter: introduce hash_and_copy_to_iter helper

Allow consumers that want to use iov iterator helpers and also update
a predefined hash calculation online when copying data. This is useful
when copying incoming network buffers to a local iterator and calculate
a digest on the incoming stream. nvme-tcp host driver that will be
introduced in following patches is the first consumer via
skb_copy_and_hash_datagram_iter.

Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sagi Grimberg <sagi@lightbitslabs.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

include/linux/uio.h

@@ -11,6 +11,7 @@
 
 #include <linux/kernel.h>
 #include <linux/thread_info.h>
+#include <crypto/hash.h>
 #include <uapi/linux/uio.h>
 
 struct page;
@@ -269,6 +270,8 @@ static inline void iov_iter_reexpand(struct iov_iter *i, size_t count)
 size_t csum_and_copy_to_iter(const void *addr, size_t bytes, void *csump, struct iov_iter *i);
 size_t csum_and_copy_from_iter(void *addr, size_t bytes, __wsum *csum, struct iov_iter *i);
 bool csum_and_copy_from_iter_full(void *addr, size_t bytes, __wsum *csum, struct iov_iter *i);
+size_t hash_and_copy_to_iter(const void *addr, size_t bytes, void *hashp,
+		struct iov_iter *i);
 
 int import_iovec(int type, const struct iovec __user * uvector,
 		 unsigned nr_segs, unsigned fast_segs,

lib/iov_iter.c

@@ -6,6 +6,7 @@
 #include <linux/vmalloc.h>
 #include <linux/splice.h>
 #include <net/checksum.h>
+#include <linux/scatterlist.h>
 
 #define PIPE_PARANOIA /* for now */
 
@@ -1511,6 +1512,21 @@ size_t csum_and_copy_to_iter(const void *addr, size_t bytes, void *csump,
 }
 EXPORT_SYMBOL(csum_and_copy_to_iter);
 
+size_t hash_and_copy_to_iter(const void *addr, size_t bytes, void *hashp,
+		struct iov_iter *i)
+{
+	struct ahash_request *hash = hashp;
+	struct scatterlist sg;
+	size_t copied;
+
+	copied = copy_to_iter(addr, bytes, i);
+	sg_init_one(&sg, addr, copied);
+	ahash_request_set_crypt(hash, &sg, NULL, copied);
+	crypto_ahash_update(hash);
+	return copied;
+}
+EXPORT_SYMBOL(hash_and_copy_to_iter);
+
 int iov_iter_npages(const struct iov_iter *i, int maxpages)
 {
 	size_t size = i->count;