upper layer. Until now, unionfs prevents to use that kind of
file system as upper layer. This time, I changed to allow
that kind of file system as upper layer. By this change, you
can use whiteout not supporting file system (e.g., especially
for tmpfs) as upper layer. It's very useful for combination of
tmpfs as upper layer and read only file system as lower layer.
By difinition, without whiteout support from the file system
backing the upper layer, there is no way that delete and rename
operations on lower layer objects can be done. EOPNOTSUPP is
returned for this kind of operations as generated by VOP_WHITEOUT()
along with any others which would make modifica tions to the
lower layer, such as chmod(1).
This change is suggested by ed.
Submitted by: ed
(it is established practice) and ``-o whiteout=whenneeded'' is less
disk-space using mode especially for resource restricted environments
like embedded environments. (Contributed by Ed Schouten. Thanks)
Submitted by: Masanori Ozawa <ozawa@ongs.co.jp> (unionfs developer)
Reviewed by: jeff, kensmith
Approved by: re (kensmith)
MFC after: 1 week
and Daichi GOTO <daichi@FreeBSD.org> for submitting this
major rewrite of unionfs. This rewrite was done to
try to solve many of the longstanding crashing and locking
issues in the existing unionfs implementation. This
implementation also adds a 'MASQUERADE mode', which allows
the user to set different user, group, and file permission
modes in the upper layer.
Submitted by: daichi, Masanori OZAWA
Reviewed by: rodrigc (modified for minor style issues)
