iov_iter: Kunit tests for copying to/from an iterator

Add some kunit tests for page extraction for ITER_BVEC, ITER_KVEC and
ITER_XARRAY type iterators.  ITER_UBUF and ITER_IOVEC aren't dealt with
as they require userspace VM interaction.  ITER_DISCARD isn't dealt with
either as that does nothing.

Signed-off-by: David Howells <dhowells@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: David Hildenbrand <david@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/Kconfig.debug

@@ -2237,6 +2237,17 @@ config TEST_DIV64
 
 	  If unsure, say N.
 
+config TEST_IOV_ITER
+	tristate "Test iov_iter operation" if !KUNIT_ALL_TESTS
+	depends on KUNIT
+	default KUNIT_ALL_TESTS
+	help
+	  Enable this to turn on testing of the operation of the I/O iterator
+	  (iov_iter). This test is executed only once during system boot (so
+	  affects only boot time), or at module load time.
+
+	  If unsure, say N.
+
 config KPROBES_SANITY_TEST
 	tristate "Kprobes sanity tests" if !KUNIT_ALL_TESTS
 	depends on DEBUG_KERNEL

lib/Makefile

@@ -64,6 +64,7 @@ obj-$(CONFIG_TEST_BITOPS) += test_bitops.o
 CFLAGS_test_bitops.o += -Werror
 obj-$(CONFIG_CPUMASK_KUNIT_TEST) += cpumask_kunit.o
 obj-$(CONFIG_TEST_SYSCTL) += test_sysctl.o
+obj-$(CONFIG_TEST_IOV_ITER) += kunit_iov_iter.o
 obj-$(CONFIG_HASH_KUNIT_TEST) += test_hash.o
 obj-$(CONFIG_TEST_IDA) += test_ida.o
 obj-$(CONFIG_TEST_UBSAN) += test_ubsan.o