Posted Jan 11, 2007 9:45 UTC (Thu) by smurf
Parent article: Unionfs
Ubuntu has been shipping their kernels with unionfs (and squashfs) for a year now, in order to support live CDs properly.
In that case, modifying unionfs parts from behind the scenes is Not A Problem because the r/w branch is hidden by the clever way the initramfs sets up the file system structure -- the unionfs is mounted at /root, and then /root is move-mounted on top of /.
But I can certainly attest to its fragility in the general case -- trying to restore an unionfs filesystem by simply pulling the r/w part from a disk dump does cause a crash pretty much immediately afterwards: unionfs sees some cached directory entries which do not have its data structure attached, and BUG()s out.
to post comments)