Linux 5.16: type member of iov_iter renamed iter_type

The iov_iter->type member was renamed iov_iter->iter_type. However,
while looking into this, realized that in 2018 a iov_iter_type(*iov)
accessor function was introduced. So if that is present, use it,
otherwise fall back to trying the existing behavior of directly
accessing type from iov_iter.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Coleman Kane <ckane@colemankane.org>
Closes openzfs#12819

config/kernel-vfs-iov_iter.m4

@@ -74,6 +74,14 @@ AC_DEFUN([ZFS_AC_KERNEL_SRC_VFS_IOV_ITER], [
 
 		bytes = copy_from_iter((void *)&buf, size, &iter);
 	])
+
+	ZFS_LINUX_TEST_SRC([iov_iter_type], [
+		#include <linux/fs.h>
+		#include <linux/uio.h>
+	],[
+		struct iov_iter iter = { 0 };
+		__attribute__((unused)) enum iter_type i = iov_iter_type(&iter);
+	])
 ])
 
 AC_DEFUN([ZFS_AC_KERNEL_VFS_IOV_ITER], [
@@ -149,6 +157,20 @@ AC_DEFUN([ZFS_AC_KERNEL_VFS_IOV_ITER], [
 		enable_vfs_iov_iter="no"
 	])
 
+	dnl #
+	dnl # This checks for iov_iter_type() in linux/uio.h. It is not
+	dnl # required, however, and the module will compiled without it
+	dnl # using direct access of the member attribute
+	dnl #
+	AC_MSG_CHECKING([whether iov_iter_type() is available])
+	ZFS_LINUX_TEST_RESULT([iov_iter_type], [
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_IOV_ITER_TYPE, 1,
+		    [iov_iter_type() is available])
+	],[
+		AC_MSG_RESULT(no)
+	])
+
 	dnl #
 	dnl # As of the 4.9 kernel support is provided for iovecs, kvecs,
 	dnl # bvecs and pipes in the iov_iter structure.  As long as the

module/os/linux/zfs/zpl_file.c

@@ -250,11 +250,17 @@ 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,
+	    iov_iter_type(to) & ITER_KVEC ? UIO_SYSSPACE : UIO_USERSPACE,
+	    count, skip);
 #else
 	zfs_uio_iovec_init(uio, to->iov, to->nr_segs, pos,
 	    to->type & ITER_KVEC ? UIO_SYSSPACE : UIO_USERSPACE,
 	    count, skip);
 #endif
+#endif
 }
 
 static ssize_t