cifs: Use iterate_and_advance*() routines directly for hashing

Replace the bespoke cifs iterators of ITER_BVEC and ITER_KVEC to do hashing
with iterate_and_advance_kernel() - a variant on iterate_and_advance() that
only supports kernel-internal ITER_* types and not UBUF/IOVEC types.

The bespoke ITER_XARRAY is left because we don't really want to be calling
crypto_shash_update() under the RCU read lock for large amounts of data;
besides, ITER_XARRAY is going to be phased out.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Steve French <sfrench@samba.org>
cc: Paulo Alcantara <pc@manguebit.com>
cc: Tom Talpey <tom@talpey.com>
cc: Enzo Matsumiya <ematsumiya@suse.de>
cc: linux-cifs@vger.kernel.org
Link: https://lore.kernel.org/r/20240814203850.2240469-24-dhowells@redhat.com/ # v2
Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 47 insertions, 0 deletions

diff --git a/include/linux/iov_iter.h b/include/linux/iov_iter.h
index a223370a59a7..c4aa58032faf 100644
--- a/include/linux/iov_iter.h
+++ b/include/linux/iov_iter.h
@@ -328,4 +328,51 @@ size_t iterate_and_advance(struct iov_iter *iter, size_t len, void *priv,
 	return iterate_and_advance2(iter, len, priv, NULL, ustep, step);
 }
 
+/**
+ * iterate_and_advance_kernel - Iterate over a kernel-internal iterator
+ * @iter: The iterator to iterate over.
+ * @len: The amount to iterate over.
+ * @priv: Data for the step functions.
+ * @priv2: More data for the step functions.
+ * @step: Function for other iterators; given kernel addresses.
+ *
+ * Iterate over the next part of an iterator, up to the specified length.  The
+ * buffer is presented in segments, which for kernel iteration are broken up by
+ * physical pages and mapped, with the mapped address being presented.
+ *
+ * [!] Note This will only handle BVEC, KVEC, FOLIOQ, XARRAY and DISCARD-type
+ * iterators; it will not handle UBUF or IOVEC-type iterators.
+ *
+ * A step functions, @step, must be provided, one for handling mapped kernel
+ * addresses and the other is given user addresses which have the potential to
+ * fault since no pinning is performed.
+ *
+ * The step functions are passed the address and length of the segment, @priv,
+ * @priv2 and the amount of data so far iterated over (which can, for example,
+ * be added to @priv to point to the right part of a second buffer).  The step
+ * functions should return the amount of the segment they didn't process (ie. 0
+ * indicates complete processsing).
+ *
+ * This function returns the amount of data processed (ie. 0 means nothing was
+ * processed and the value of @len means processes to completion).
+ */
+static __always_inline
+size_t iterate_and_advance_kernel(struct iov_iter *iter, size_t len, void *priv,
+				  void *priv2, iov_step_f step)
+{
+	if (unlikely(iter->count < len))
+		len = iter->count;
+	if (unlikely(!len))
+		return 0;
+	if (iov_iter_is_bvec(iter))
+		return iterate_bvec(iter, len, priv, priv2, step);
+	if (iov_iter_is_kvec(iter))
+		return iterate_kvec(iter, len, priv, priv2, step);
+	if (iov_iter_is_folioq(iter))
+		return iterate_folioq(iter, len, priv, priv2, step);
+	if (iov_iter_is_xarray(iter))
+		return iterate_xarray(iter, len, priv, priv2, step);
+	return iterate_discard(iter, len, priv, priv2, step);
+}
+
 #endif /* _LINUX_IOV_ITER_H */