I am trying to use EncFS in conjunction with btrfs and I ran into a
weird situation which I think is caused by statvfs being called on a
btrfs subvolume.
In particular, when I do something like the following:
statvfs("/mnt/btrfs-volume/some-subvolume")
then all mounted FUSE file-systems receive a GETATTR request. This is
strange because it happens to FUSE file-systems completely unrelated to
/mnt/btrfs-volume.
This can cause serious problems with some FUSE file-systems such as
EncFS. For instance, suppose that you have an EncFS file-systems as
follows:
encfs /mnt/btrfs-volume/some-subvolume /home/user/private
Whenever you do statvfs("/home/user/private") then EncFS will internally
call statvfs("/mnt/btrfs-volume/some-subvolume") but this in turn will
cause the FUSE method getattr to be called. This cycle of dependencies
results in a deadlock.
STEP TO REPRODUCE:
1. btrfs subvolume create /mnt/btrfs-volume/private
2. mkdir /home/user/private
3. encfs /mnt/btrfs-volume/private /home/user/private
4. [ do statvfs("/home/user/private") ]
In step 4, stavfs will never return and /home/user/private will become
unresponsive.
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