Linux 6.15: mkdir now returns struct dentry *

The intent is that the filesystem may have a reference to an "old"
version of the new directory, eg if it was keeping it alive because a
remote NFS client still had it open.

We don't need anything like that, so this really just changes things so
we return error codes encoded in pointers.

Sponsored-by: https://despairlabs.com/sponsor/
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Pavel Snajdr <snajpa@snajpa.net>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes #17229

config/kernel-mkdir.m4

@@ -2,6 +2,22 @@ dnl #
 dnl # Supported mkdir() interfaces checked newest to oldest.
 dnl #
 AC_DEFUN([ZFS_AC_KERNEL_SRC_MKDIR], [
+	dnl #
+	dnl # 6.15 API change
+	dnl # mkdir() returns struct dentry *
+	dnl #
+	ZFS_LINUX_TEST_SRC([mkdir_return_dentry], [
+		#include <linux/fs.h>
+
+		static struct dentry *mkdir(struct mnt_idmap *idmap,
+			struct inode *inode, struct dentry *dentry,
+			umode_t umode) { return dentry; }
+		static const struct inode_operations
+		    iops __attribute__ ((unused)) = {
+			.mkdir = mkdir,
+		};
+	],[])
+
 	dnl #
 	dnl # 6.3 API change
 	dnl # mkdir() takes struct mnt_idmap * as the first arg
@@ -59,29 +75,40 @@ AC_DEFUN([ZFS_AC_KERNEL_SRC_MKDIR], [
 
 AC_DEFUN([ZFS_AC_KERNEL_MKDIR], [
 	dnl #
-	dnl # 6.3 API change
+	dnl # 6.15 API change
-	dnl # mkdir() takes struct mnt_idmap * as the first arg
+	dnl # mkdir() returns struct dentry *
 	dnl #
-	AC_MSG_CHECKING([whether iops->mkdir() takes struct mnt_idmap*])
+	AC_MSG_CHECKING([whether iops->mkdir() returns struct dentry*])
-	ZFS_LINUX_TEST_RESULT([mkdir_mnt_idmap], [
+	ZFS_LINUX_TEST_RESULT([mkdir_return_dentry], [
 		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE_IOPS_MKDIR_IDMAP, 1,
+		AC_DEFINE(HAVE_IOPS_MKDIR_DENTRY, 1,
-		    [iops->mkdir() takes struct mnt_idmap*])
+		    [iops->mkdir() returns struct dentry*])
 	],[
-		AC_MSG_RESULT(no)
-
 		dnl #
-		dnl # 5.12 API change
+		dnl # 6.3 API change
-		dnl # The struct user_namespace arg was added as the first argument to
+		dnl # mkdir() takes struct mnt_idmap * as the first arg
-		dnl # mkdir() of the iops structure.
 		dnl #
-		AC_MSG_CHECKING([whether iops->mkdir() takes struct user_namespace*])
+		AC_MSG_CHECKING([whether iops->mkdir() takes struct mnt_idmap*])
-		ZFS_LINUX_TEST_RESULT([mkdir_user_namespace], [
+		ZFS_LINUX_TEST_RESULT([mkdir_mnt_idmap], [
 			AC_MSG_RESULT(yes)
-			AC_DEFINE(HAVE_IOPS_MKDIR_USERNS, 1,
+			AC_DEFINE(HAVE_IOPS_MKDIR_IDMAP, 1,
-			    [iops->mkdir() takes struct user_namespace*])
+			    [iops->mkdir() takes struct mnt_idmap*])
 		],[
 			AC_MSG_RESULT(no)
+
+			dnl #
+			dnl # 5.12 API change
+			dnl # The struct user_namespace arg was added as the first argument to
+			dnl # mkdir() of the iops structure.
+			dnl #
+			AC_MSG_CHECKING([whether iops->mkdir() takes struct user_namespace*])
+			ZFS_LINUX_TEST_RESULT([mkdir_user_namespace], [
+				AC_MSG_RESULT(yes)
+				AC_DEFINE(HAVE_IOPS_MKDIR_USERNS, 1,
+				    [iops->mkdir() takes struct user_namespace*])
+			],[
+				AC_MSG_RESULT(no)
+			])
 		])
 	])
 ])

module/os/linux/zfs/zpl_ctldir.c

@@ -341,14 +341,20 @@ zpl_snapdir_rmdir(struct inode *dip, struct dentry *dentry)
 	return (error);
 }
 
+#if defined(HAVE_IOPS_MKDIR_USERNS)
 static int
-#ifdef HAVE_IOPS_MKDIR_USERNS
 zpl_snapdir_mkdir(struct user_namespace *user_ns, struct inode *dip,
     struct dentry *dentry, umode_t mode)
 #elif defined(HAVE_IOPS_MKDIR_IDMAP)
+static int
+zpl_snapdir_mkdir(struct mnt_idmap *user_ns, struct inode *dip,
+    struct dentry *dentry, umode_t mode)
+#elif defined(HAVE_IOPS_MKDIR_DENTRY)
+static struct dentry *
 zpl_snapdir_mkdir(struct mnt_idmap *user_ns, struct inode *dip,
     struct dentry *dentry, umode_t mode)
 #else
+static int
 zpl_snapdir_mkdir(struct inode *dip, struct dentry *dentry, umode_t mode)
 #endif
 {
@@ -376,7 +382,11 @@ zpl_snapdir_mkdir(struct inode *dip, struct dentry *dentry, umode_t mode)
 	ASSERT3S(error, <=, 0);
 	crfree(cr);
 
+#if defined(HAVE_IOPS_MKDIR_DENTRY)
+	return (ERR_PTR(error));
+#else
 	return (error);
+#endif
 }
 
 /*

module/os/linux/zfs/zpl_inode.c

@@ -374,14 +374,20 @@ zpl_unlink(struct inode *dir, struct dentry *dentry)
 	return (error);
 }
 
+#if defined(HAVE_IOPS_MKDIR_USERNS)
 static int
-#ifdef HAVE_IOPS_MKDIR_USERNS
 zpl_mkdir(struct user_namespace *user_ns, struct inode *dir,
     struct dentry *dentry, umode_t mode)
 #elif defined(HAVE_IOPS_MKDIR_IDMAP)
+static int
+zpl_mkdir(struct mnt_idmap *user_ns, struct inode *dir,
+    struct dentry *dentry, umode_t mode)
+#elif defined(HAVE_IOPS_MKDIR_DENTRY)
+static struct dentry *
 zpl_mkdir(struct mnt_idmap *user_ns, struct inode *dir,
     struct dentry *dentry, umode_t mode)
 #else
+static int
 zpl_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
 #endif
 {
@@ -390,12 +396,14 @@ zpl_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
 	znode_t *zp;
 	int error;
 	fstrans_cookie_t cookie;
-#if !(defined(HAVE_IOPS_MKDIR_USERNS) || defined(HAVE_IOPS_MKDIR_IDMAP))
+#if !(defined(HAVE_IOPS_MKDIR_USERNS) || \
+	defined(HAVE_IOPS_MKDIR_IDMAP) || defined(HAVE_IOPS_MKDIR_DENTRY))
 	zidmap_t *user_ns = kcred->user_ns;
 #endif
 
 	if (is_nametoolong(dentry)) {
-		return (-ENAMETOOLONG);
+		error = -ENAMETOOLONG;
+		goto err;
 	}
 
 	crhold(cr);
@@ -422,9 +430,14 @@ zpl_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
 	spl_fstrans_unmark(cookie);
 	kmem_free(vap, sizeof (vattr_t));
 	crfree(cr);
-	ASSERT3S(error, <=, 0);
 
+err:
+	ASSERT3S(error, <=, 0);
+#if defined(HAVE_IOPS_MKDIR_DENTRY)
+	return (error != 0 ? ERR_PTR(error) : NULL);
+#else
 	return (error);
+#endif
 }
 
 static int