Linux 6.16: remove writepage and readahead_page

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes #17443

config/kernel-pagemap-readahead-page.m4

@@ -0,0 +1,23 @@
+dnl #
+dnl # Linux 6.16 removed readahead_page
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_SRC_PAGEMAP_READAHEAD_PAGE], [
+	ZFS_LINUX_TEST_SRC([pagemap_has_readahead_page], [
+		#include <linux/pagemap.h>
+	], [
+		struct page *p __attribute__ ((unused)) = NULL;
+		struct readahead_control *ractl __attribute__ ((unused)) = NULL;
+		p = readahead_page(ractl);
+	])
+])
+
+AC_DEFUN([ZFS_AC_KERNEL_PAGEMAP_READAHEAD_PAGE], [
+	AC_MSG_CHECKING([whether readahead_page() exists])
+	ZFS_LINUX_TEST_RESULT([pagemap_has_readahead_page], [
+		AC_MSG_RESULT([yes])
+		AC_DEFINE(HAVE_PAGEMAP_READAHEAD_PAGE, 1,
+			[readahead_page() exists])
+	],[
+		AC_MSG_RESULT([no])
+	])
+])

config/kernel-vfs-writepage.m4

@@ -0,0 +1,24 @@
+dnl #
+dnl # Linux 6.16 removes address_space_operations ->writepage
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_SRC_VFS_WRITEPAGE], [
+	ZFS_LINUX_TEST_SRC([vfs_has_writepage], [
+		#include <linux/fs.h>
+
+		static const struct address_space_operations
+		    aops __attribute__ ((unused)) = {
+			.writepage = NULL,
+		};
+	],[])
+])
+
+AC_DEFUN([ZFS_AC_KERNEL_VFS_WRITEPAGE], [
+	AC_MSG_CHECKING([whether aops->writepage exists])
+	ZFS_LINUX_TEST_RESULT([vfs_has_writepage], [
+		AC_MSG_RESULT([yes])
+		AC_DEFINE(HAVE_VFS_WRITEPAGE, 1,
+			[address_space_operations->writepage exists])
+	],[
+		AC_MSG_RESULT([no])
+	])
+])

config/kernel.m4

@@ -82,6 +82,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_SRC], [
 	ZFS_AC_KERNEL_SRC_VFS_MIGRATEPAGE
 	ZFS_AC_KERNEL_SRC_VFS_FSYNC_2ARGS
 	ZFS_AC_KERNEL_SRC_VFS_READPAGES
+	ZFS_AC_KERNEL_SRC_VFS_WRITEPAGE
 	ZFS_AC_KERNEL_SRC_VFS_SET_PAGE_DIRTY_NOBUFFERS
 	ZFS_AC_KERNEL_SRC_VFS_IOV_ITER
 	ZFS_AC_KERNEL_SRC_VFS_GENERIC_COPY_FILE_RANGE
@@ -111,6 +112,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_SRC], [
 	ZFS_AC_KERNEL_SRC_STANDALONE_LINUX_STDARG
 	ZFS_AC_KERNEL_SRC_STRLCPY
 	ZFS_AC_KERNEL_SRC_PAGEMAP_FOLIO_WAIT_BIT
+	ZFS_AC_KERNEL_SRC_PAGEMAP_READAHEAD_PAGE
 	ZFS_AC_KERNEL_SRC_ADD_DISK
 	ZFS_AC_KERNEL_SRC_KTHREAD
 	ZFS_AC_KERNEL_SRC_ZERO_PAGE
@@ -197,6 +199,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_RESULT], [
 	ZFS_AC_KERNEL_VFS_MIGRATEPAGE
 	ZFS_AC_KERNEL_VFS_FSYNC_2ARGS
 	ZFS_AC_KERNEL_VFS_READPAGES
+	ZFS_AC_KERNEL_VFS_WRITEPAGE
 	ZFS_AC_KERNEL_VFS_SET_PAGE_DIRTY_NOBUFFERS
 	ZFS_AC_KERNEL_VFS_IOV_ITER
 	ZFS_AC_KERNEL_VFS_GENERIC_COPY_FILE_RANGE
@@ -226,6 +229,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_RESULT], [
 	ZFS_AC_KERNEL_STANDALONE_LINUX_STDARG
 	ZFS_AC_KERNEL_STRLCPY
 	ZFS_AC_KERNEL_PAGEMAP_FOLIO_WAIT_BIT
+	ZFS_AC_KERNEL_PAGEMAP_READAHEAD_PAGE
 	ZFS_AC_KERNEL_ADD_DISK
 	ZFS_AC_KERNEL_KTHREAD
 	ZFS_AC_KERNEL_ZERO_PAGE

include/os/linux/Makefile.am

@@ -8,6 +8,7 @@ kernel_linux_HEADERS = \
 	%D%/kernel/linux/mm_compat.h \
 	%D%/kernel/linux/mod_compat.h \
 	%D%/kernel/linux/page_compat.h \
+	%D%/kernel/linux/pagemap_compat.h \
 	%D%/kernel/linux/simd.h \
 	%D%/kernel/linux/simd_aarch64.h \
 	%D%/kernel/linux/simd_arm.h \

include/os/linux/kernel/linux/pagemap_compat.h

@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: CDDL-1.0
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or https://opensource.org/licenses/CDDL-1.0.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+
+/*
+ * Copyright (c) 2025, Rob Norris <robn@despairlabs.com>
+ */
+
+#ifndef _ZFS_PAGEMAP_COMPAT_H
+#define	_ZFS_PAGEMAP_COMPAT_H
+
+#include <linux/pagemap.h>
+
+#ifndef HAVE_PAGEMAP_READAHEAD_PAGE
+#define	readahead_page(ractl) (&(__readahead_folio(ractl)->page))
+#endif
+
+#endif

module/os/linux/zfs/zpl_file.c

@@ -36,10 +36,7 @@
 #include <sys/zfs_vfsops.h>
 #include <sys/zfs_vnops.h>
 #include <sys/zfs_project.h>
-#if defined(HAVE_VFS_SET_PAGE_DIRTY_NOBUFFERS) || \
+#include <linux/pagemap_compat.h>
-    defined(HAVE_VFS_FILEMAP_DIRTY_FOLIO)
-#include <linux/pagemap.h>
-#endif
 #include <linux/fadvise.h>
 #ifdef HAVE_VFS_FILEMAP_DIRTY_FOLIO
 #include <linux/writeback.h>
@@ -555,6 +552,7 @@ zpl_writepages(struct address_space *mapping, struct writeback_control *wbc)
 	return (result);
 }
 
+#ifdef HAVE_VFS_WRITEPAGE
 /*
  * Write out dirty pages to the ARC, this function is only required to
  * support mmap(2).  Mapped pages may be dirtied by memory operations
@@ -571,6 +569,7 @@ zpl_writepage(struct page *pp, struct writeback_control *wbc)
 
 	return (zpl_putpage(pp, wbc, &for_sync));
 }
+#endif
 
 /*
  * The flag combination which matches the behavior of zfs_space() is
@@ -1063,7 +1062,9 @@ const struct address_space_operations zpl_address_space_operations = {
 #else
 	.readpage	= zpl_readpage,
 #endif
+#ifdef HAVE_VFS_WRITEPAGE
 	.writepage	= zpl_writepage,
+#endif
 	.writepages	= zpl_writepages,
 	.direct_IO	= zpl_direct_IO,
 #ifdef HAVE_VFS_SET_PAGE_DIRTY_NOBUFFERS