Linux 6.4 compat: iter_iov() function now used to get old iov member

The iov_iter->iov member is now iov_iter->__iov and must be accessed via
the accessor function iter_iov(). Create a wrapper that is conditionally
compiled to use the access method appropriate for the target kernel
version.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Brian Atkinson <batkinson@lanl.gov>
Signed-off-by: Coleman Kane <ckane@colemankane.org>
Closes #15100

config/kernel-vfs-iov_iter.m4

@@ -93,6 +93,14 @@ AC_DEFUN([ZFS_AC_KERNEL_SRC_VFS_IOV_ITER], [
 		struct iov_iter iter = { 0 };
 		__attribute__((unused)) enum iter_type i = iov_iter_type(&iter);
 	])
+
+	ZFS_LINUX_TEST_SRC([iter_iov], [
+		#include <linux/fs.h>
+		#include <linux/uio.h>
+	],[
+		struct iov_iter iter = { 0 };
+		__attribute__((unused)) const struct iovec *iov = iter_iov(&iter);
+	])
 ])
 
 AC_DEFUN([ZFS_AC_KERNEL_VFS_IOV_ITER], [
@@ -201,4 +209,19 @@ AC_DEFUN([ZFS_AC_KERNEL_VFS_IOV_ITER], [
 		AC_DEFINE(HAVE_VFS_IOV_ITER, 1,
 		    [All required iov_iter interfaces are available])
 	])
+
+	dnl #
+	dnl # Kernel 6.5 introduces the iter_iov() function that returns the
+	dnl # __iov member of an iov_iter*. The iov member was renamed to this
+	dnl # __iov member, and is intended to be accessed via the helper
+	dnl # function now.
+	dnl #
+	AC_MSG_CHECKING([whether iter_iov() is available])
+	ZFS_LINUX_TEST_RESULT([iter_iov], [
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_ITER_IOV, 1,
+		    [iter_iov() is available])
+	],[
+		AC_MSG_RESULT(no)
+	])
 ])

include/os/linux/spl/sys/uio.h

@@ -173,4 +173,10 @@ zfs_uio_iov_iter_init(zfs_uio_t *uio, struct iov_iter *iter, offset_t offset,
 }
 #endif
 
+#if defined(HAVE_ITER_IOV)
+#define	zfs_uio_iter_iov(iter)	iter_iov((iter))
+#else
+#define	zfs_uio_iter_iov(iter)	(iter)->iov
+#endif
+
 #endif /* SPL_UIO_H */

module/os/linux/zfs/zpl_file.c

@@ -300,17 +300,15 @@ zpl_uio_init(zfs_uio_t *uio, struct kiocb *kiocb, struct iov_iter *to,
 {
 #if defined(HAVE_VFS_IOV_ITER)
 	zfs_uio_iov_iter_init(uio, to, pos, count, skip);
-#else
-#ifdef HAVE_IOV_ITER_TYPE
-	zfs_uio_iovec_init(uio, to->iov, to->nr_segs, pos,
+#elif defined(HAVE_IOV_ITER_TYPE)
+	zfs_uio_iovec_init(uio, zfs_uio_iter_iov(to), to->nr_segs, pos,
 	    iov_iter_type(to) & ITER_KVEC ? UIO_SYSSPACE : UIO_USERSPACE,
 	    count, skip);
 #else
-	zfs_uio_iovec_init(uio, to->iov, to->nr_segs, pos,
+	zfs_uio_iovec_init(uio, zfs_uio_iter_iov(to), to->nr_segs, pos,
 	    to->type & ITER_KVEC ? UIO_SYSSPACE : UIO_USERSPACE,
 	    count, skip);
 #endif
-#endif
 }
 
 static ssize_t