btrfs: add simple debugfs interface

Help during debugging to export various interesting infromation and
tunables without the need of extra mount options or ioctls.

Usage:
* declare your variable in sysfs.h, and include where you need it
* define the variable in sysfs.c and make it visible via
  debugfs_create_TYPE

Depends on CONFIG_DEBUG_FS.

Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Josef Bacik <jbacik@fb.com>

2 files changed, 32 insertions, 6 deletions

diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index 865f4cf9a769..c5eb2143dc66 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -24,6 +24,7 @@
 #include <linux/kobject.h>
 #include <linux/bug.h>
 #include <linux/genhd.h>
+#include <linux/debugfs.h>
 
 #include "ctree.h"
 #include "disk-io.h"
@@ -599,6 +600,12 @@ static int add_device_membership(struct btrfs_fs_info *fs_info)
 /* /sys/fs/btrfs/ entry */
 static struct kset *btrfs_kset;
 
+/* /sys/kernel/debug/btrfs */
+static struct dentry *btrfs_debugfs_root_dentry;
+
+/* Debugging tunables and exported data */
+u64 btrfs_debugfs_test;
+
 int btrfs_sysfs_add_one(struct btrfs_fs_info *fs_info)
 {
         int error;
@@ -642,27 +649,41 @@ failure:
         return error;
 }
 
+static int btrfs_init_debugfs(void)
+{
+#ifdef CONFIG_DEBUG_FS
+        btrfs_debugfs_root_dentry = debugfs_create_dir("btrfs", NULL);
+        if (!btrfs_debugfs_root_dentry)
+                return -ENOMEM;
+
+        debugfs_create_u64("test", S_IRUGO | S_IWUGO, btrfs_debugfs_root_dentry,
+                        &btrfs_debugfs_test);
+#endif
+        return 0;
+}
+
 int btrfs_init_sysfs(void)
 {
         int ret;
+
         btrfs_kset = kset_create_and_add("btrfs", NULL, fs_kobj);
         if (!btrfs_kset)
                 return -ENOMEM;
 
-        init_feature_attrs();
+        ret = btrfs_init_debugfs();
+        if (ret)
+                return ret;
 
+        init_feature_attrs();
         ret = sysfs_create_group(&btrfs_kset->kobj, &btrfs_feature_attr_group);
-        if (ret) {
-                kset_unregister(btrfs_kset);
-                return ret;
-        }
 
-        return 0;
+        return ret;
 }
 
 void btrfs_exit_sysfs(void)
 {
         sysfs_remove_group(&btrfs_kset->kobj, &btrfs_feature_attr_group);
         kset_unregister(btrfs_kset);
+        debugfs_remove_recursive(btrfs_debugfs_root_dentry);
 }
 
diff --git a/fs/btrfs/sysfs.h b/fs/btrfs/sysfs.h
index f3cea3710d44..9ab576318a84 100644
--- a/fs/btrfs/sysfs.h
+++ b/fs/btrfs/sysfs.h
@@ -1,6 +1,11 @@
 #ifndef _BTRFS_SYSFS_H_
 #define _BTRFS_SYSFS_H_
 
+/*
+ * Data exported through sysfs
+ */
+extern u64 btrfs_debugfs_test;
+
 enum btrfs_feature_set {
         FEAT_COMPAT,
         FEAT_COMPAT_RO,