Amir Goldstein: > WIP is at https://github.com/amir73il/linux/commits/ovl-index-dir. > I could post patches, but I rather not spam you now unless asked. > > So far it does the job of creating the non-dir upper hardlinks in index > dir and unbreaking hardlinks on copy up (ignoring concurrent copy up > of 2 lower hardlinks for now). The very basic design (as a first step) is close to aufs' "pseudo-link". (from linux/Documentation/filesystems/aufs/design/0strcut.txt) ---------------------------------------- Pseudo-link ---------------------------------------------------------------------- Assume "fileA" exists on the lower readonly branch only and it is hardlinked to "fileB" on the branch. When you write something to fileA, aufs copies-up it to the upper writable branch. Additionally aufs creates a hardlink under the Pseudo-link Directory of the writable branch. The inode of a pseudo-link is kept in aufs super_block as a simple list. If fileB is read after unlinking fileA, aufs returns filedata from the pseudo-link instead of the lower readonly branch. Because the pseudo-link is based upon the inode, to keep the inode number by xino (see above) is essentially necessary. All the hardlinks under the Pseudo-link Directory of the writable branch should be restored in a proper location later. Aufs provides a utility to do this. The userspace helpers executed at remounting and unmounting aufs by default. During this utility is running, it puts aufs into the pseudo-link maintenance mode. In this mode, only the process which began the maintenance mode (and its child processes) is allowed to operate in aufs. Some other processes which are not related to the pseudo-link will be allowed to run too, but the rest have to return an error or wait until the maintenance mode ends. If a process already acquires an inode mutex (in VFS), it has to return an error. ---------------------------------------- How do you think about the lifetime of the entries under ovl-index-dir? Aufs has a user-space utility to restore/reproduce all hardlinks on the upper writable layer, and it removes the entries under Pseudo-link Directory. J. R. Okajima -- To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
