From 18daf228d7e63a84571cd6fe122f578a52005eef Mon Sep 17 00:00:00 2001
From: Pavel Snajdr <snajpa@snajpa.net>
Date: Thu, 7 Nov 2019 12:07:08 -0500
Subject: [PATCH] renameat2: add EL7 compatibility handling

EL7 has backported renameat2(2) support, but this was done by creating a
wrapper struct around the inode_operations struct and adding the rename2
callback to the wrapping struct. The semantics are the same as the
upstream callback, so just detect and use the wrapper.

Since we only need this wrapper for rename2 (and renaming is a directory
operation) we only use the wrapper for the directory iops struct.

Signed-off-by: Pavel Snajdr <snajpa@snajpa.net>
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
 config/kernel-rename.m4         | 27 +++++++++++++++++++++++++++
 include/os/linux/zfs/sys/zpl.h  |  4 ++++
 module/os/linux/zfs/zfs_znode.c |  5 +++++
 module/os/linux/zfs/zpl_inode.c |  9 +++++++++
 4 files changed, 45 insertions(+)

diff --git a/config/kernel-rename.m4 b/config/kernel-rename.m4
index 8d06f57cb13a..a2b0800ab4d2 100644
--- a/config/kernel-rename.m4
+++ b/config/kernel-rename.m4
@@ -36,6 +36,24 @@ AC_DEFUN([ZFS_AC_KERNEL_SRC_RENAME], [
 		};
 	],[])
 
+	dnl #
+	dnl # EL7 compatibility
+	dnl #
+	dnl # EL7 has backported renameat2 support, but it's done by defining a
+	dnl # separate iops wrapper structure that takes the .renameat2 function.
+	dnl #
+	ZFS_LINUX_TEST_SRC([dir_inode_operations_wrapper_rename2], [
+		#include <linux/fs.h>
+		int rename2_fn(struct inode *sip, struct dentry *sdp,
+			struct inode *tip, struct dentry *tdp,
+			unsigned int flags) { return 0; }
+
+		static const struct inode_operations_wrapper
+		    iops __attribute__ ((unused)) = {
+			.rename2 = rename2_fn,
+		};
+	],[])
+
 	dnl #
 	dnl # 5.12 API change,
 	dnl #
@@ -78,6 +96,15 @@ AC_DEFUN([ZFS_AC_KERNEL_RENAME], [
 					[iops->rename() wants flags])
 			],[
 				AC_MSG_RESULT(no)
+
+				AC_MSG_CHECKING([whether struct inode_operations_wrapper takes .rename2()])
+				ZFS_LINUX_TEST_RESULT([dir_inode_operations_wrapper_rename2], [
+					AC_MSG_RESULT(yes)
+					AC_DEFINE(HAVE_RENAME2_OPERATIONS_WRAPPER, 1,
+						[struct inode_operations_wrapper takes .rename2()])
+				],[
+					AC_MSG_RESULT(no)
+				])
 			])
 		])
 	])
diff --git a/include/os/linux/zfs/sys/zpl.h b/include/os/linux/zfs/sys/zpl.h
index 54f3fa0fdb0f..f0e4a27d8f25 100644
--- a/include/os/linux/zfs/sys/zpl.h
+++ b/include/os/linux/zfs/sys/zpl.h
@@ -42,7 +42,11 @@ extern void zpl_vap_init(vattr_t *vap, struct inode *dir,
     umode_t mode, cred_t *cr);
 
 extern const struct inode_operations zpl_inode_operations;
+#ifdef HAVE_RENAME2_OPERATIONS_WRAPPER
+extern const struct inode_operations_wrapper zpl_dir_inode_operations;
+#else
 extern const struct inode_operations zpl_dir_inode_operations;
+#endif
 extern const struct inode_operations zpl_symlink_inode_operations;
 extern const struct inode_operations zpl_special_inode_operations;
 extern dentry_operations_t zpl_dentry_operations;
diff --git a/module/os/linux/zfs/zfs_znode.c b/module/os/linux/zfs/zfs_znode.c
index 6015aea62dca..84275898aef0 100644
--- a/module/os/linux/zfs/zfs_znode.c
+++ b/module/os/linux/zfs/zfs_znode.c
@@ -414,7 +414,12 @@ zfs_inode_set_ops(zfsvfs_t *zfsvfs, struct inode *ip)
 		break;
 
 	case S_IFDIR:
+#ifdef HAVE_RENAME2_OPERATIONS_WRAPPER
+		ip->i_flags |= S_IOPS_WRAPPER;
+		ip->i_op = &zpl_dir_inode_operations.ops;
+#else
 		ip->i_op = &zpl_dir_inode_operations;
+#endif
 		ip->i_fop = &zpl_dir_file_operations;
 		ITOZ(ip)->z_zn_prefetch = B_TRUE;
 		break;
diff --git a/module/os/linux/zfs/zpl_inode.c b/module/os/linux/zfs/zpl_inode.c
index b019bcbf90c0..71fdf304bea7 100644
--- a/module/os/linux/zfs/zpl_inode.c
+++ b/module/os/linux/zfs/zpl_inode.c
@@ -728,7 +728,12 @@ const struct inode_operations zpl_inode_operations = {
 #endif /* CONFIG_FS_POSIX_ACL */
 };
 
+#ifdef HAVE_RENAME2_OPERATIONS_WRAPPER
+const struct inode_operations_wrapper zpl_dir_inode_operations = {
+	.ops = {
+#else
 const struct inode_operations zpl_dir_inode_operations = {
+#endif
 	.create		= zpl_create,
 	.lookup		= zpl_lookup,
 	.link		= zpl_link,
@@ -761,6 +766,10 @@ const struct inode_operations zpl_dir_inode_operations = {
 #endif /* HAVE_SET_ACL */
 	.get_acl	= zpl_get_acl,
 #endif /* CONFIG_FS_POSIX_ACL */
+#ifdef HAVE_RENAME2_OPERATIONS_WRAPPER
+	},
+	.rename2	= zpl_rename2,
+#endif
 };
 
 const struct inode_operations zpl_symlink_inode_operations = {