debugfs: allow to store an additional opaque pointer at file creation

Set by debugfs_create_file_aux(name, mode, parent, data, aux, fops).
Plain debugfs_create_file() has it set to NULL.
Accessed by debugfs_get_aux(file).

Convenience macros for numeric opaque data - debugfs_create_file_aux_num
and debugfs_get_aux_num, resp.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Link: https://lore.kernel.org/r/20250112080705.141166-5-viro@zeniv.linux.org.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/debugfs/file.c

@@ -47,6 +47,12 @@ const struct file_operations debugfs_noop_file_operations = {
 
 #define F_DENTRY(filp) ((filp)->f_path.dentry)
 
+const void *debugfs_get_aux(const struct file *file)
+{
+	return DEBUGFS_I(file_inode(file))->aux;
+}
+EXPORT_SYMBOL_GPL(debugfs_get_aux);
+
 const struct file_operations *debugfs_real_fops(const struct file *filp)
 {
 	struct debugfs_fsdata *fsd = F_DENTRY(filp)->d_fsdata;

fs/debugfs/inode.c

@@ -424,6 +424,7 @@ static struct dentry *end_creating(struct dentry *dentry)
 
 static struct dentry *__debugfs_create_file(const char *name, umode_t mode,
 				struct dentry *parent, void *data,
+				const void *aux,
 				const struct file_operations *proxy_fops,
 				const void *real_fops)
 {
@@ -458,6 +459,7 @@ static struct dentry *__debugfs_create_file(const char *name, umode_t mode,
 		proxy_fops = &debugfs_noop_file_operations;
 	inode->i_fop = proxy_fops;
 	DEBUGFS_I(inode)->raw = real_fops;
+	DEBUGFS_I(inode)->aux = aux;
 
 	d_instantiate(dentry, inode);
 	fsnotify_create(d_inode(dentry->d_parent), dentry);
@@ -466,19 +468,21 @@ static struct dentry *__debugfs_create_file(const char *name, umode_t mode,
 
 struct dentry *debugfs_create_file_full(const char *name, umode_t mode,
 					struct dentry *parent, void *data,
+					const void *aux,
 					const struct file_operations *fops)
 {
-	return __debugfs_create_file(name, mode, parent, data,
+	return __debugfs_create_file(name, mode, parent, data, aux,
 				&debugfs_full_proxy_file_operations,
 				fops);
 }
 EXPORT_SYMBOL_GPL(debugfs_create_file_full);
 
 struct dentry *debugfs_create_file_short(const char *name, umode_t mode,
-					 struct dentry *parent, void *data,
+					struct dentry *parent, void *data,
-					 const struct debugfs_short_fops *fops)
+					const void *aux,
+					const struct debugfs_short_fops *fops)
 {
-	return __debugfs_create_file(name, mode, parent, data,
+	return __debugfs_create_file(name, mode, parent, data, aux,
 				&debugfs_full_short_proxy_file_operations,
 				fops);
 }
@@ -516,7 +520,7 @@ struct dentry *debugfs_create_file_unsafe(const char *name, umode_t mode,
 				   const struct file_operations *fops)
 {
 
-	return __debugfs_create_file(name, mode, parent, data,
+	return __debugfs_create_file(name, mode, parent, data, NULL,
 				&debugfs_open_proxy_file_operations,
 				fops);
 }

fs/debugfs/internal.h

@@ -19,6 +19,7 @@ struct debugfs_inode_info {
 		const struct debugfs_short_fops *short_fops;
 		debugfs_automount_t automount;
 	};
+	const void *aux;
 };
 
 static inline struct debugfs_inode_info *DEBUGFS_I(struct inode *inode)

include/linux/debugfs.h

@@ -79,9 +79,11 @@ struct debugfs_short_fops {
 
 struct dentry *debugfs_create_file_full(const char *name, umode_t mode,
 					struct dentry *parent, void *data,
+					const void *aux,
 					const struct file_operations *fops);
 struct dentry *debugfs_create_file_short(const char *name, umode_t mode,
 					 struct dentry *parent, void *data,
+					 const void *aux,
 					 const struct debugfs_short_fops *fops);
 
 /**
@@ -126,7 +128,15 @@ struct dentry *debugfs_create_file_short(const char *name, umode_t mode,
 		 const struct debugfs_short_fops *: debugfs_create_file_short,	\
 		 struct file_operations *: debugfs_create_file_full,		\
 		 struct debugfs_short_fops *: debugfs_create_file_short)	\
-		(name, mode, parent, data, fops)
+		(name, mode, parent, data, NULL, fops)
+
+#define debugfs_create_file_aux(name, mode, parent, data, aux, fops)		\
+	_Generic(fops,								\
+		 const struct file_operations *: debugfs_create_file_full,	\
+		 const struct debugfs_short_fops *: debugfs_create_file_short,	\
+		 struct file_operations *: debugfs_create_file_full,		\
+		 struct debugfs_short_fops *: debugfs_create_file_short)	\
+		(name, mode, parent, data, aux, fops)
 
 struct dentry *debugfs_create_file_unsafe(const char *name, umode_t mode,
 				   struct dentry *parent, void *data,
@@ -153,6 +163,7 @@ void debugfs_remove(struct dentry *dentry);
 void debugfs_lookup_and_remove(const char *name, struct dentry *parent);
 
 const struct file_operations *debugfs_real_fops(const struct file *filp);
+const void *debugfs_get_aux(const struct file *file);
 
 int debugfs_file_get(struct dentry *dentry);
 void debugfs_file_put(struct dentry *dentry);
@@ -259,6 +270,14 @@ static inline struct dentry *debugfs_lookup(const char *name,
 	return ERR_PTR(-ENODEV);
 }
 
+static inline struct dentry *debugfs_create_file_aux(const char *name,
+					umode_t mode, struct dentry *parent,
+					void *data, void *aux,
+					const void *fops)
+{
+	return ERR_PTR(-ENODEV);
+}
+
 static inline struct dentry *debugfs_create_file(const char *name, umode_t mode,
 					struct dentry *parent, void *data,
 					const void *fops)
@@ -312,6 +331,7 @@ static inline void debugfs_lookup_and_remove(const char *name,
 { }
 
 const struct file_operations *debugfs_real_fops(const struct file *filp);
+void *debugfs_get_aux(const struct file *file);
 
 static inline int debugfs_file_get(struct dentry *dentry)
 {
@@ -452,6 +472,11 @@ static inline ssize_t debugfs_read_file_str(struct file *file,
 
 #endif
 
+#define debugfs_create_file_aux_num(name, mode, parent, data, n, fops) \
+	debugfs_create_file_aux(name, mode, parent, data, \
+				(void *)(unsigned long)n, fops)
+#define debugfs_get_aux_num(f) (unsigned long)debugfs_get_aux(f)
+
 /**
  * debugfs_create_xul - create a debugfs file that is used to read and write an
  * unsigned long value, formatted in hexadecimal