On Thu, Aug 26, 2010 at 08:33:45PM +0200, Miklos Szeredi wrote: > From: Miklos Szeredi <mszeredi@xxxxxxx> > > This union filesystem is a hybrid of entirely filesystem based > (unionfs, aufs) and entierly VFS based (union mounts) solutions. > > The dentry tree is duplicated from the underlying filesystems, this > enables fast cached lookups without adding special support into the > VFS. This uses slightly more memory than union mounts, but dentries > are relatively small. > > Inode structures are only duplicated for directories. Regular files, > symlinks and special files each share a single inode. This means that > locking victim for unlink is a quasi-filesystem lock, which is > suboptimal, but could be worked around in the VFS. > > Opening non directories results in the open forwarded to the > underlying filesystem. This makes the behavior very similar to union > mounts (with the same limitations vs. fchmod/fchown on O_RDONLY file > descriptors). > > Usage: > > mount -t union -olowerdir=/union/lower,upperdir=/union/upper union /mnt/union > > Supported: > > - all operations > > Missing: > > - upgrade credentials for copy-up > - ensure that filesystems part of the union are not modified outside > the union Just a note that the infrastructure I wrote to do this last bullet point for union mounts (hard read-only count plus mount checks) is completely compatible with hybrid union fs. -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
