On Mon, Jul 30, 2007 at 06:13:35PM +0200, Jan Blunck wrote: > Introduce white-out support to ext2. I think storing whiteouts on the branches is wrong. It creates all sort of nasty cases when people actually try to use unioning. Imagine a (no-so unlikely) scenario where you have 2 unions, and they share a branch. If you create a whiteout in one union on that shared branch, the whiteout magically affects the other union as well! Whiteouts are a union-level construct, and therefore storing them at the branch level is wrong. If you store whiteouts on the branches, you'll probably want readdir to not include them. That's relatively cheap if you have a whiteout bit in the inode, but I don't think filesystems should be forced to use up rather prescious inode bits for whiteouts/opaqueness [1]. Really the only sane way of keeping track of whiteouts seems some external store. We did an experiment with Unionfs, and moving the whiteout handling to effectively a "library" that did all the dirty work cleaned up the code considerably [2,3]. > Known Bugs: > - Needs a reserved inode number for white-outs > - S_OPAQUE isn't persistently stored Out of curiosity, how do you keep track of opaqueness while the fs is mounted? Josef 'Jeff' Sipek. [1] http://www.mail-archive.com/linux-fsdevel@xxxxxxxxxxxxxxx/msg02904.html [2] http://www.filesystems.org/unionfs-odf.txt [3] http://download.filesystems.org/unionfs/unionfs-2.0-odf/linux-2.6.20-rc6-odf1.diff.gz -- UNIX is user-friendly ... it's just selective about who it's friends are - 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
