fs: proc: store PDE()->data into inode->i_private

PDE_DATA(inode) is introduced to get user private data and hide the
layout of struct proc_dir_entry.  The inode->i_private is used to do the
same thing as well.  Save a copy of user private data to inode->
i_private when proc inode is allocated.  This means the user also can
get their private data by inode->i_private.

Introduce pde_data() to wrap inode->i_private so that we can remove
PDE_DATA() from fs/proc/generic.c and make PTE_DATE() as a wrapper of
pde_data().  It will be easier if we decide to remove PDE_DATE() in the
future.

Link: https://lkml.kernel.org/r/20211124081956.87711-1-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Alexey Gladkov <gladkov.alexey@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: songmuchun

fs/proc/generic.c

@@ -791,12 +791,6 @@ void proc_remove(struct proc_dir_entry *de)
 }
 EXPORT_SYMBOL(proc_remove);
 
-void *PDE_DATA(const struct inode *inode)
-{
-	return __PDE_DATA(inode);
-}
-EXPORT_SYMBOL(PDE_DATA);
-
 /*
  * Pull a user buffer into memory and pass it to the file's write handler if
  * one is supplied.  The ->write() method is permitted to modify the

fs/proc/inode.c

@@ -650,6 +650,7 @@ struct inode *proc_get_inode(struct super_block *sb, struct proc_dir_entry *de)
 		return NULL;
 	}
 
+	inode->i_private = de->data;
 	inode->i_ino = de->low_ino;
 	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
 	PROC_I(inode)->pde = de;

fs/proc/internal.h

@@ -115,11 +115,6 @@ static inline struct proc_dir_entry *PDE(const struct inode *inode)
 	return PROC_I(inode)->pde;
 }
 
-static inline void *__PDE_DATA(const struct inode *inode)
-{
-	return PDE(inode)->data;
-}
-
 static inline struct pid *proc_pid(const struct inode *inode)
 {
 	return PROC_I(inode)->pid;

include/linux/proc_fs.h

@@ -110,7 +110,18 @@ extern struct proc_dir_entry *proc_create_data(const char *, umode_t,
 struct proc_dir_entry *proc_create(const char *name, umode_t mode, struct proc_dir_entry *parent, const struct proc_ops *proc_ops);
 extern void proc_set_size(struct proc_dir_entry *, loff_t);
 extern void proc_set_user(struct proc_dir_entry *, kuid_t, kgid_t);
-extern void *PDE_DATA(const struct inode *);
+
+/*
+ * Obtain the private data passed by user through proc_create_data() or
+ * related.
+ */
+static inline void *pde_data(const struct inode *inode)
+{
+	return inode->i_private;
+}
+
+#define PDE_DATA(i)	pde_data(i)
+
 extern void *proc_get_parent_data(const struct inode *);
 extern void proc_remove(struct proc_dir_entry *);
 extern void remove_proc_entry(const char *, struct proc_dir_entry *);