Update the xattr_set() interface for the 5.12 user_namespace API changes

Some more additions that update the ZPL_XATTR_SET_WRAPPER() macro such
that it will build interface functions that adopt the struct
user_namespace* argument as the second arg, if that is the
implementation required in the kernel (determined by configure). This
was added to support idmapped FS mounts in Linux 5.12.

Signed-off-by: Coleman Kane <[email protected]>

Author: ckane

config/kernel-xattr-handler.m4

@@ -152,7 +152,7 @@ dnl #
 dnl # Supported xattr handler set() interfaces checked newest to oldest.
 dnl #
 AC_DEFUN([ZFS_AC_KERNEL_SRC_XATTR_HANDLER_SET], [
-	ZFS_LINUX_TEST_SRC([xattr_handler_set_dentry_inode_user_ns], [
+	ZFS_LINUX_TEST_SRC([xattr_handler_set_userns], [
 		#include <linux/xattr.h>
 
 		int set(const struct xattr_handler *handler,
@@ -214,16 +214,17 @@ AC_DEFUN([ZFS_AC_KERNEL_XATTR_HANDLER_SET], [
 	dnl # struct user_namespace* was inserted as arg #2
 	dnl #
 	AC_MSG_CHECKING([whether xattr_handler->set() wants dentry, inode, and user_namespace])
-	ZFS_LINUX_TEST_RESULT([xattr_handler_set_dentry_inode_user_ns], [
+	ZFS_LINUX_TEST_RESULT([xattr_handler_set_userns], [
 		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE_XATTR_SET_DENTRY_INODE_USER_NS, 1,
-		    [xattr_handler->set() wants dentry, inode, and user_namespace])
+		AC_DEFINE(HAVE_XATTR_SET_USERNS, 1,
+		    [xattr_handler->set() takes user_namespace])
 	],[
 		dnl #
 		dnl # 4.7 API change,
 		dnl # The xattr_handler->set() callback was changed to take both
 		dnl # dentry and inode.
 		dnl #
+		AC_MSG_RESULT(no)
 		AC_MSG_CHECKING([whether xattr_handler->set() wants dentry and inode])
 		ZFS_LINUX_TEST_RESULT([xattr_handler_set_dentry_inode], [
 			AC_MSG_RESULT(yes)

include/os/linux/kernel/linux/xattr_compat.h

@@ -119,12 +119,27 @@ fn(struct dentry *dentry, const char *name, void *buffer, size_t size,	\
 #error "Unsupported kernel"
 #endif
 
+/*
+ * 5.12 API change,
+ * The xattr_handler->set() callback was changed to take the
+ * struct user_namespace* as the first arg, to support idmapped
+ * mounts.
+ */
+#if defined(HAVE_XATTR_SET_USERNS)
+#define	ZPL_XATTR_SET_WRAPPER(fn)					\
+static int								\
+fn(const struct xattr_handler *handler, struct user_namespace *user_ns, \
+    struct dentry *dentry, struct inode *inode, const char *name,	\
+    const void *buffer, size_t size, int flags)	\
+{									\
+	return (__ ## fn(inode, name, buffer, size, flags));		\
+}
 /*
  * 4.7 API change,
  * The xattr_handler->set() callback was changed to take a both dentry and
  * inode, because the dentry might not be attached to an inode yet.
  */
-#if defined(HAVE_XATTR_SET_DENTRY_INODE)
+#elif defined(HAVE_XATTR_SET_DENTRY_INODE)
 #define	ZPL_XATTR_SET_WRAPPER(fn)					\
 static int								\
 fn(const struct xattr_handler *handler, struct dentry *dentry,		\