On Mon, 18 May 2009, Jan Blunck wrote: > Here is another post of the VFS based union mount implementation. > > Traditionally the mount operation is opaque, which means that the content of > the mount point, the directory where the file system is mounted on, is hidden > by the content of the mounted file system's root directory until the file > system is unmounted again. Unlike the traditional UNIX mount mechanism, that > hides the contents of the mount point, a union mount presents a view as if > both filesystems are merged together. Although only the topmost layer of the > mount stack can be altered, it appears as if transparent file system mounts > allow any file to be created, modified or deleted. > > Most people know the concepts and features of union mounts from other > operating systems like Sun's Translucent Filesystem, Plan9 or BSD. For an > in-depth review of union mounts and other unioning file systems, see: > > http://lwn.net/Articles/324291/ > http://lwn.net/Articles/325369/ > http://lwn.net/Articles/327738/ > > Here are the key features of this implementation: > - completely VFS based > - does not change the namespace stacking > - directory listings have duplicate entries removed in the kernel > - writable unions: only the topmost file system layer may be writable > - writable unions: new whiteout filetype handled inside the kernel > > Major changes since last post: > - Updated the whiteout patches: > - DCACHE_WHITEOUT flag set on a negative dentry > - uses filetype instead of reserved inode number on EXT2 > - Copy-up directories during lookup > - Implemented fallthru support for in-kernel readdir() as proposed by > Valerie Aurora (Henson) Does this copy up directories persistently? If so, does this implementation no longer supports union of all read-only branches? Thanks, Miklos -- 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
