[PATCH v14 7/9] 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. Add a separate
debugfs_symlinks xarray and use that to track symlinks. The reaper
workqueue job will remove symlinks before their corresponding dentries.

Signed-off-by: Jeff Layton <jlay...@kernel.org>
---
 include/linux/ref_tracker.h | 11 +++++++++++
 lib/ref_tracker.c           | 47 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+)

diff --git a/include/linux/ref_tracker.h b/include/linux/ref_tracker.h
index 
28bbf436a8f4646cfac181d618195a9460bda196..e1323de93bf6b891aa14ad8d9b4b28d02e10f9f7
 100644
--- a/include/linux/ref_tracker.h
+++ b/include/linux/ref_tracker.h
@@ -29,6 +29,7 @@ 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 */
 
@@ -36,6 +37,11 @@ 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,
@@ -85,6 +91,11 @@ 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 
4f1c4fe5e6b1274b6aeb733a3f8c06d1dff003f5..a78741308a2c2dc7aff65519970ad081b59e0de5
 100644
--- a/lib/ref_tracker.c
+++ b/lib/ref_tracker.c
@@ -44,11 +44,13 @@ struct ref_tracker_dir_stats {
  * dentries asynchronously.
  */
 static struct xarray           debugfs_dentries;
+static struct xarray           debugfs_symlinks;
 static struct work_struct      debugfs_reap_worker;
 
 #define REF_TRACKER_DIR_DEAD   XA_MARK_0
 static inline void ref_tracker_debugfs_mark(struct ref_tracker_dir *dir)
 {
+       xa_set_mark(&debugfs_symlinks, (unsigned long)dir, 
REF_TRACKER_DIR_DEAD);
        xa_set_mark(&debugfs_dentries, (unsigned long)dir, 
REF_TRACKER_DIR_DEAD);
        schedule_work(&debugfs_reap_worker);
 }
@@ -446,6 +448,45 @@ 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];
+       struct dentry *symlink, *dentry;
+       va_list args;
+       int ret;
+
+       symlink = xa_load(&debugfs_symlinks, (unsigned long)dir);
+       dentry = xa_load(&debugfs_dentries, (unsigned long)dir);
+
+       /* Already created?*/
+       if (symlink && !xa_is_err(symlink))
+               return;
+
+       if (!dentry || xa_is_err(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)) {
+               symlink = debugfs_create_symlink(name, ref_tracker_debug_dir,
+                                                dentry->d_name.name);
+               if (!IS_ERR(symlink)) {
+                       void *old;
+
+                       old = xa_store(&debugfs_symlinks, (unsigned long)dir,
+                                      symlink, GFP_KERNEL);
+                       if (xa_is_err(old))
+                               debugfs_remove(symlink);
+                       else
+                               WARN_ON_ONCE(old);
+               }
+       }
+}
+EXPORT_SYMBOL(ref_tracker_dir_symlink);
+
 static void debugfs_reap_work(struct work_struct *work)
 {
        struct dentry *dentry;
@@ -454,6 +495,11 @@ static void debugfs_reap_work(struct work_struct *work)
 
        do {
                reaped = false;
+               xa_for_each_marked(&debugfs_symlinks, index, dentry, 
REF_TRACKER_DIR_DEAD) {
+                       xa_erase(&debugfs_symlinks, index);
+                       debugfs_remove(dentry);
+                       reaped = true;
+               }
                xa_for_each_marked(&debugfs_dentries, index, dentry, 
REF_TRACKER_DIR_DEAD) {
                        xa_erase(&debugfs_dentries, index);
                        debugfs_remove(dentry);
@@ -466,6 +512,7 @@ static int __init ref_tracker_debugfs_init(void)
 {
        INIT_WORK(&debugfs_reap_worker, debugfs_reap_work);
        xa_init_flags(&debugfs_dentries, XA_FLAGS_LOCK_IRQ);
+       xa_init_flags(&debugfs_symlinks, XA_FLAGS_LOCK_IRQ);
        ref_tracker_debug_dir = debugfs_create_dir("ref_tracker", NULL);
        return 0;
 }

-- 
2.49.0