libfs: Add helper to choose dentry operations at mount-time

In preparation to drop the similar helper that sets d_op at lookup time,
add a version to set the right d_op filesystem-wide, through sb->s_d_op.
The operations structures are shared across filesystems supporting
fscrypt and/or casefolding, therefore we can keep it in common libfs
code.

Reviewed-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20240221171412.10710-7-krisman@suse.de
Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>

Author: krisman

fs/libfs.c

@@ -1818,6 +1818,34 @@ void generic_set_encrypted_ci_d_ops(struct dentry *dentry)
 }
 EXPORT_SYMBOL(generic_set_encrypted_ci_d_ops);
 
+/**
+ * generic_set_sb_d_ops - helper for choosing the set of
+ * filesystem-wide dentry operations for the enabled features
+ * @sb: superblock to be configured
+ *
+ * Filesystems supporting casefolding and/or fscrypt can call this
+ * helper at mount-time to configure sb->s_d_op to best set of dentry
+ * operations required for the enabled features. The helper must be
+ * called after these have been configured, but before the root dentry
+ * is created.
+ */
+void generic_set_sb_d_ops(struct super_block *sb)
+{
+#if IS_ENABLED(CONFIG_UNICODE)
+	if (sb->s_encoding) {
+		sb->s_d_op = &generic_ci_dentry_ops;
+		return;
+	}
+#endif
+#ifdef CONFIG_FS_ENCRYPTION
+	if (sb->s_cop) {
+		sb->s_d_op = &generic_encrypted_dentry_ops;
+		return;
+	}
+#endif
+}
+EXPORT_SYMBOL(generic_set_sb_d_ops);
+
 /**
  * inode_maybe_inc_iversion - increments i_version
  * @inode: inode with the i_version that should be updated

include/linux/fs.h

@@ -3281,6 +3281,7 @@ extern int generic_file_fsync(struct file *, loff_t, loff_t, int);
 extern int generic_check_addressable(unsigned, u64);
 
 extern void generic_set_encrypted_ci_d_ops(struct dentry *dentry);
+extern void generic_set_sb_d_ops(struct super_block *sb);
 
 static inline bool sb_has_encoding(const struct super_block *sb)
 {