[PATCH v9 07/10] ref_tracker: add a way to create a symlink to the ref_tracker_dir debugfs file

[Jeff Layton]

Add the ability for a subsystem to add a user-friendly symlink that
points to a ref_tracker_dir's debugfs file.

Signed-off-by: Jeff Layton <jlayton at kernel.org>
---
 include/linux/ref_tracker.h | 13 +++++++++++++
 lib/ref_tracker.c           | 28 ++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/include/linux/ref_tracker.h b/include/linux/ref_tracker.h
index dd289fdda12b1a10197912f5796f97002e785aaf..ddc5a7b2bd84692bbc1e1ae67674ec2c6857e1ec 100644
--- a/include/linux/ref_tracker.h
+++ b/include/linux/ref_tracker.h
@@ -22,6 +22,7 @@ struct ref_tracker_dir {
 	const char		*class; /* object classname */
 #ifdef CONFIG_DEBUG_FS
 	struct dentry		*dentry;
+	struct dentry		*symlink;
 #endif
 	char			name[32];
 #endif
@@ -32,6 +33,7 @@ struct ref_tracker_dir {
 #ifdef CONFIG_DEBUG_FS
 
 void ref_tracker_dir_debugfs(struct ref_tracker_dir *dir);
+void ref_tracker_dir_symlink(struct ref_tracker_dir *dir, const char *fmt, ...);
 
 #else /* CONFIG_DEBUG_FS */
 
@@ -39,6 +41,11 @@ static inline void ref_tracker_dir_debugfs(struct ref_tracker_dir *dir)
 {
 }
 
+static inline __ostream_printf
+void ref_tracker_dir_symlink(struct ref_tracker_dir *dir, const char *fmt, ...)
+{
+}
+
 #endif /* CONFIG_DEBUG_FS */
 
 static inline void ref_tracker_dir_init(struct ref_tracker_dir *dir,
@@ -56,6 +63,7 @@ static inline void ref_tracker_dir_init(struct ref_tracker_dir *dir,
 	dir->class = class;
 #ifdef CONFIG_DEBUG_FS
 	dir->dentry = NULL;
+	dir->symlink = NULL;
 #endif
 	strscpy(dir->name, name, sizeof(dir->name));
 	ref_tracker_dir_debugfs(dir);
@@ -91,6 +99,11 @@ static inline void ref_tracker_dir_debugfs(struct ref_tracker_dir *dir)
 {
 }
 
+static inline __ostream_printf
+void ref_tracker_dir_symlink(struct ref_tracker_dir *dir, const char *fmt, ...)
+{
+}
+
 static inline void ref_tracker_dir_exit(struct ref_tracker_dir *dir)
 {
 }
diff --git a/lib/ref_tracker.c b/lib/ref_tracker.c
index 1df12625d80cc7cff65d9f6be89e1dd5c5ffb7f6..5e84e5fd78e147a036d4adb511e657da07866a55 100644
--- a/lib/ref_tracker.c
+++ b/lib/ref_tracker.c
@@ -390,8 +390,36 @@ void ref_tracker_dir_debugfs(struct ref_tracker_dir *dir)
 }
 EXPORT_SYMBOL(ref_tracker_dir_debugfs);
 
+void __ostream_printf ref_tracker_dir_symlink(struct ref_tracker_dir *dir, const char *fmt, ...)
+{
+	char name[NAME_MAX + 1];
+	va_list args;
+	int ret;
+
+	/* Already created, or dentry doesn't exist? Do nothing */
+	if (!IS_ERR_OR_NULL(dir->symlink) || IS_ERR_OR_NULL(dir->dentry))
+		return;
+
+	va_start(args, fmt);
+	ret = vsnprintf(name, sizeof(name), fmt, args);
+	va_end(args);
+	name[sizeof(name) - 1] = '\0';
+
+	if (ret < sizeof(name))
+		dir->symlink = debugfs_create_symlink(name, ref_tracker_debug_dir,
+						      dir->dentry->d_name.name);
+	else
+		dir->symlink = ERR_PTR(-ENAMETOOLONG);
+
+	if (IS_ERR(dir->symlink))
+		pr_warn("ref_tracker: unable to create debugfs symlink for %s: %pe\n",
+			name, dir->symlink);
+}
+EXPORT_SYMBOL(ref_tracker_dir_symlink);
+
 static void ref_tracker_debugfs_remove(struct ref_tracker_dir *dir)
 {
+	debugfs_remove(dir->symlink);
 	debugfs_remove(dir->dentry);
 }
 

-- 
2.49.0