There was a critical flaw in the previous implementation of open-behind.
When an open is done in the background, it's necessary to take a
reference on the fd_t object because once we "fake" the open answer,
the fd could be destroyed. However as long as there's a reference,
the release function won't be called. So, if the application closes
the file descriptor without having actually opened it, there will
always remain at least 1 reference, causing a leak.
To avoid this problem, the previous implementation didn't take a
reference on the fd_t, so there were races where the fd could be
destroyed while it was still in use.
To fix this, I've implemented a new xlator cbk that gets called from
fuse when the application closes a file descriptor.
The whole logic of handling background opens have been simplified and
it's more efficient now. Only if the fop needs to be delayed until an
open completes, a stub is created. Otherwise no memory allocations are
needed.
Correctly handling the close request while the open is still pending
has added a bit of complexity, but overall normal operation is simpler.
Change-Id: I6376a5491368e0e1c283cc452849032636261592
Fixes: #1225
Signed-off-by: Xavi Hernandez <xhernandez@redhat.com>