On Fri, Nov 13, 2009 at 01:46:15PM -0500, Erez Zadok wrote: > In message <20091113174631.GD19656@shell>, Valerie Aurora writes: > > Fallthrus were invented as a placeholders for readdir() on a > > union-mounted directory - basically, to use the top-level file > > system's readdir() cookie mechanism. Fallthrus are persistent > > directory entries and are implemented by the underlying file system - > > such as ext2 or tmpfs - in whatever way it sees fit. We've > > implemented them for ext2 in two ways: as a regular directory entry > > with a magic inode number, and as a regular directory entry with a > > special file type. > > Other than a possible improvement to ->rename, what's wrong with the idea of > a special dirent flag? I kinda liked that idea: it's simple and requires > only a small amount of change to lower file systems. Any idea in which you > have to record the whiteouts using an actual file or inode is more > cumbersome. You have it right - the major advantage is a possible simplification to rename(). > > Recently, David Woodhouse suggested implementing fallthrus as > > full-length symlinks with a special flag. > > Where does this "special flag" go? Is it persistent? Is it new? Would > that mean having to change lower file systems to teach them about this flag? > > Is there a way of doing it w/o having to change lower f/s code at all? > That'll be a major advantage if possible. I can't think of a way to do it without using up namespace - but perhaps there is some part of the symlink target namespace that has no valid meaning that we could use instead, like Arnd's self symlink. -VAL -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
