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Date: Thu, 05 Aug 2010 13:13:55 +0200 From: Miklos Szeredi <miklos@...redi.hu> To: Valerie Aurora <vaurora@...hat.com> CC: miklos@...redi.hu, viro@...iv.linux.org.uk, jblunck@...e.de, hch@...radead.org, linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, tytso@....edu, linux-ext4@...r.kernel.org Subject: Re: [PATCH 14/38] fallthru: ext2 fallthru support On Wed, 4 Aug 2010, Valerie Aurora wrote: > > Another idea is to use an internal inode and make all fallthroughs be > > hard links to that. > > > > I think the same would work for whiteouts as well. I don't like the > > fact that whiteouts are invisible even when not mounted as part of a > > union. > > I don't know if this helps, but I just wrote support for removing ext2 > whiteouts and fallthrus using tune2fs and e2fsck. I think this does > what people want from a "visible" whiteout feature without adding more > complexity to the VFS. It also takes away all consideration of race > conditions and dentry conversion that happens with online removal of > whiteouts and fallthrus. > > What are your thoughts on what a visible whiteout/fallthru would look > like? Best would be if it didn't need any modification to filesystems. All this having to upgrade util-linux, e2fsprogs, having incompatible filesystem features is a pain for users (just been through that). What we already have in most filesystems: - extended attributes, e.g. use the system.union.* namespace and denote whiteouts and falltroughs with such an attribute - hard links to make sure a separate inode is not necessary for each whiteout/fallthrough entry - some way for the user to easily identify such files when not mounted as part of a union e.g. make it a symlink pointing to "(deleted)" or whatever Later the extended attributes can also be used for other things like e.g. chmod()/chown() only copying up metadata, not data, and indicating that data is still found on the lower layers. Miklos -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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