Hello, On Fri, Aug 14, 2009 at 11:23:22PM +0200, Thomas Schwinge wrote: > On Fri, Aug 14, 2009 at 10:26:10PM +0300, Sergiu Ivanov wrote: > > > You are right -- if a node contains more node_ulfs entries than there > > are registered in ulfs_chain, then something has gone seriously > > corrupted. However, I have a question, which is related to > > consistency (again *sigh*): ulfs_get_num is invoked in two places > > only: in netfs_attempt_sync and in node_init_root (node.c:533 in my > > code version). In node_init_root the return value of ulfs_get_num is > > checked in an if statement. Is it alright to check this value via an > > assert in netfs_attempt_sync? Or should I change the handling of the > > return value in node_init_root instead? > > I don't really know the unionfs code, but if these two structures are > always meant to be kept synchronized (which I don't really know, so you'd > have to verify that -- or unify these structures, which was the long-term > plan, isn't it?), then a fatal error (assert) is OK.
I don't remember any snippets of the unionfs code where the ULFS list and the list of ports in the root node were intentionally kept unsynchronized. However, it seems I can see the reason for the lists being maintained separately: *each* unionfs node contains a list of ports to the corresponding nodes in the underlying filesystems. If one would like to keep *both* the information about the filesystems *and* the ports to their root nodes in *a single* place, one would have two choices: either add something like a ``port'' field to each entry in the ulfs_chain, thus duplicating the port list in the netfs_root_node and still leaving the necessity of synchronizing things explicitly; or keep the information about the filesystems (i.e. the information stored in ulfs_chain) in *every* node, thus duplicating the same bits of information across a (potentially) large number of locations. Unfourtunately, it seems that solving this issue without deep thinking is not something easily achieved :-( Regards, scolobb
