Replace generic_file_splice_read with filemap_splice_read

The generic_file_splice_read function was removed in Linux 6.5 in favor
of filemap_splice_read. Add an autoconf test for filemap_splice_read and
use it if it is found as the handler for .splice_read in the
file_operations struct. Additionally, ITER_PIPE was removed in 6.5. This
change removes the ITER_* macros that OpenZFS doesn't use from being
tested in config/kernel-vfs-iov_iter.m4. The removal of ITER_PIPE was
causing the test to fail, which also affected the code responsible for
setting the .splice_read handler, above. That behavior caused run-time
panics on Linux 6.5.

Signed-off-by: Coleman Kane <ckane@colemankane.org>

config/kernel-filemap-splice-read.m4

@@ -0,0 +1,25 @@
+AC_DEFUN([ZFS_AC_KERNEL_SRC_FILEMAP_SPLICE_READ], [
+	dnl #
+	dnl # Kernel 6.5 - generic_file_splice_read was removed in favor
+	dnl # of filemap_splice_read for the .splice_read member of the
+	dnl # file_operations struct.
+	dnl #
+	ZFS_LINUX_TEST_SRC([has_filemap_splice_read], [
+		#include <linux/fs.h>
+
+		struct file_operations fops __attribute__((unused)) = {
+			.splice_read = filemap_splice_read,
+		};
+	],[])
+])
+
+AC_DEFUN([ZFS_AC_KERNEL_FILEMAP_SPLICE_READ], [
+	AC_MSG_CHECKING([whether filemap_splice_read() exists])
+	ZFS_LINUX_TEST_RESULT([has_filemap_splice_read], [
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_FILEMAP_SPLICE_READ, 1,
+		    [filemap_splice_read exists])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])

config/kernel-vfs-iov_iter.m4

@@ -6,8 +6,7 @@ AC_DEFUN([ZFS_AC_KERNEL_SRC_VFS_IOV_ITER], [
 		#include <linux/fs.h>
 		#include <linux/uio.h>
 	],[
-		int type __attribute__ ((unused)) =
-		    ITER_IOVEC | ITER_KVEC | ITER_BVEC | ITER_PIPE;
+		int type __attribute__ ((unused)) = ITER_KVEC;
 	])
 
 	ZFS_LINUX_TEST_SRC([iov_iter_advance], [

config/kernel.m4

@@ -161,6 +161,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_SRC], [
 	ZFS_AC_KERNEL_SRC_WRITEPAGE_T
 	ZFS_AC_KERNEL_SRC_RECLAIMED
 	ZFS_AC_KERNEL_SRC_REGISTER_SYSCTL_TABLE
+	ZFS_AC_KERNEL_SRC_FILEMAP_SPLICE_READ
 	case "$host_cpu" in
 		powerpc*)
 			ZFS_AC_KERNEL_SRC_CPU_HAS_FEATURE
@@ -301,6 +302,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_RESULT], [
 	ZFS_AC_KERNEL_WRITEPAGE_T
 	ZFS_AC_KERNEL_RECLAIMED
 	ZFS_AC_KERNEL_REGISTER_SYSCTL_TABLE
+	ZFS_AC_KERNEL_FILEMAP_SPLICE_READ
 	case "$host_cpu" in
 		powerpc*)
 			ZFS_AC_KERNEL_CPU_HAS_FEATURE

module/os/linux/zfs/zpl_file.c

@@ -1323,7 +1323,11 @@ const struct file_operations zpl_file_operations = {
 	.read_iter	= zpl_iter_read,
 	.write_iter	= zpl_iter_write,
 #ifdef HAVE_VFS_IOV_ITER
+#ifdef HAVE_FILEMAP_SPLICE_READ
+	.splice_read	= filemap_splice_read,
+#else
 	.splice_read	= generic_file_splice_read,
+#endif
 	.splice_write	= iter_file_splice_write,
 #endif
 #else