2 files changed, 87 insertions, 0 deletions

diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index 5b326cd60a4a..9e217b581903 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -26,20 +26,64 @@
 #include "ctree.h"
 #include "disk-io.h"
 #include "transaction.h"
+#include "sysfs.h"
+
+static ssize_t btrfs_feature_attr_show(struct kobject *kobj,
+                                       struct kobj_attribute *a, char *buf)
+{
+        return snprintf(buf, PAGE_SIZE, "0\n");
+}
+
+BTRFS_FEAT_ATTR_INCOMPAT(mixed_backref, MIXED_BACKREF);
+BTRFS_FEAT_ATTR_INCOMPAT(default_subvol, DEFAULT_SUBVOL);
+BTRFS_FEAT_ATTR_INCOMPAT(mixed_groups, MIXED_GROUPS);
+BTRFS_FEAT_ATTR_INCOMPAT(compress_lzo, COMPRESS_LZO);
+BTRFS_FEAT_ATTR_INCOMPAT(compress_lzov2, COMPRESS_LZOv2);
+BTRFS_FEAT_ATTR_INCOMPAT(big_metadata, BIG_METADATA);
+BTRFS_FEAT_ATTR_INCOMPAT(extended_iref, EXTENDED_IREF);
+BTRFS_FEAT_ATTR_INCOMPAT(raid56, RAID56);
+BTRFS_FEAT_ATTR_INCOMPAT(skinny_metadata, SKINNY_METADATA);
+
+static struct attribute *btrfs_supported_feature_attrs[] = {
+        BTRFS_FEAT_ATTR_PTR(mixed_backref),
+        BTRFS_FEAT_ATTR_PTR(default_subvol),
+        BTRFS_FEAT_ATTR_PTR(mixed_groups),
+        BTRFS_FEAT_ATTR_PTR(compress_lzo),
+        BTRFS_FEAT_ATTR_PTR(compress_lzov2),
+        BTRFS_FEAT_ATTR_PTR(big_metadata),
+        BTRFS_FEAT_ATTR_PTR(extended_iref),
+        BTRFS_FEAT_ATTR_PTR(raid56),
+        BTRFS_FEAT_ATTR_PTR(skinny_metadata),
+        NULL
+};
+
+static const struct attribute_group btrfs_feature_attr_group = {
+        .name = "features",
+        .attrs = btrfs_supported_feature_attrs,
+};
 
 /* /sys/fs/btrfs/ entry */
 static struct kset *btrfs_kset;
 
 int btrfs_init_sysfs(void)
 {
+        int ret;
         btrfs_kset = kset_create_and_add("btrfs", NULL, fs_kobj);
         if (!btrfs_kset)
                 return -ENOMEM;
+
+        ret = sysfs_create_group(&btrfs_kset->kobj, &btrfs_feature_attr_group);
+        if (ret) {
+                kset_unregister(btrfs_kset);
+                return ret;
+        }
+
         return 0;
 }
 
 void btrfs_exit_sysfs(void)
 {
+        sysfs_remove_group(&btrfs_kset->kobj, &btrfs_feature_attr_group);
         kset_unregister(btrfs_kset);
 }
 
diff --git a/fs/btrfs/sysfs.h b/fs/btrfs/sysfs.h
new file mode 100644
index 000000000000..863e031ed1c1
--- /dev/null
+++ b/fs/btrfs/sysfs.h
@@ -0,0 +1,43 @@
+#ifndef _BTRFS_SYSFS_H_
+#define _BTRFS_SYSFS_H_
+
+enum btrfs_feature_set {
+        FEAT_COMPAT,
+        FEAT_COMPAT_RO,
+        FEAT_INCOMPAT,
+        FEAT_MAX
+};
+
+#define __INIT_KOBJ_ATTR(_name, _mode, _show, _store)                   \
+{                                                                       \
+        .attr   = { .name = __stringify(_name), .mode = _mode },        \
+        .show   = _show,                                                \
+        .store  = _store,                                               \
+}
+
+struct btrfs_feature_attr {
+        struct kobj_attribute kobj_attr;
+        enum btrfs_feature_set feature_set;
+        u64 feature_bit;
+};
+
+#define BTRFS_FEAT_ATTR(_name, _feature_set, _prefix, _feature_bit)          \
+static struct btrfs_feature_attr btrfs_attr_##_name = {                      \
+        .kobj_attr = __INIT_KOBJ_ATTR(_name, S_IRUGO,                        \
+                                      btrfs_feature_attr_show, NULL),        \
+        .feature_set    = _feature_set,                                      \
+        .feature_bit    = _prefix ##_## _feature_bit,                        \
+}
+#define BTRFS_FEAT_ATTR_PTR(_name)    (&btrfs_attr_##_name.kobj_attr.attr)
+
+#define BTRFS_FEAT_ATTR_COMPAT(name, feature) \
+        BTRFS_FEAT_ATTR(name, FEAT_COMPAT, BTRFS_FEATURE_COMPAT, feature)
+#define BTRFS_FEAT_ATTR_COMPAT_RO(name, feature) \
+        BTRFS_FEAT_ATTR(name, FEAT_COMPAT_RO, BTRFS_FEATURE_COMPAT, feature)
+#define BTRFS_FEAT_ATTR_INCOMPAT(name, feature) \
+        BTRFS_FEAT_ATTR(name, FEAT_INCOMPAT, BTRFS_FEATURE_INCOMPAT, feature)
+
+/* convert from attribute */
+#define to_btrfs_feature_attr(a) \
+                        container_of(a, struct btrfs_feature_attr, kobj_attr)
+#endif /* _BTRFS_SYSFS_H_ */