On Fri, Jan 29, 2016 at 01:55:31PM +0000, Filipe Manana wrote:

On Thu, Jan 21, 2016 at 6:32 PM, David Sterba [off-list ref] wrote:

quoted

The files under /sys/fs/UUID/features get out of sync with the actual
incompat bits set for the filesystem if they change after mount. We're
going to sync them and need a helper to do that.

Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/sysfs.c | 30 ++++++++++++++++++++++++++++++
 fs/btrfs/sysfs.h |  3 +++
 2 files changed, 33 insertions(+)

diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index 906f7ed6fc80..6986886243bf 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c

@@ -782,6 +782,36 @@ int btrfs_sysfs_add_mounted(struct btrfs_fs_info *fs_info)
        return error;
 }

+
+/*
+ * Change per-fs features in /sys/fs/btrfs/UUID/features to match current
+ * values in superblock. Call after any changes to incompat/compat_ro flags
+ */
+void btrfs_sysfs_feature_update(struct btrfs_fs_info *fs_info,
+               u64 bit, enum btrfs_feature_set set)
+{
+       struct btrfs_fs_devices *fs_devs;
+       struct kobject *fsid_kobj;
+       u64 features;
+       int ret;
+
+       if (!fs_info)
+               return;
+
+       features = get_features(fs_info, set);
+       ASSERT(bit & supported_feature_masks[set]);
+
+       fs_devs = fs_info->fs_devices;
+       fsid_kobj = &fs_devs->fsid_kobj;
+
+       /*
+        * FIXME: this is too heavy to update just one value, ideally we'd like
+        * to use sysfs_update_group but some refactoring is needed first.
+        */
+       sysfs_remove_group(fsid_kobj, &btrfs_feature_attr_group);
+       ret = sysfs_create_group(fsid_kobj, &btrfs_feature_attr_group);

Did you try to run all xfstests with this?

I'm getting very often lots of warnings in btrfs tests 060 to 074:

I did, but I have the compression remount tests ratelimited a bit
because of bugs in mount on my test box.

I might wait on the whole pull until before rc3, so we can sort this out
properly.

-chris