btrfs: publish supported featured in sysfs

This patch adds the ability to publish supported features to sysfs under
/sys/fs/btrfs/features.

The files are module-wide and export which features the kernel supports.

The content, for now, is just "0\n".

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 44 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);
 }