On Tue, May 10, 2016 at 04:36:56PM -0700, James Bottomley wrote:
> +static int shiftfs_rename2(struct inode *olddir, struct dentry *old,
> + struct inode *newdir, struct dentry *new,
> + unsigned int flags)
> +{
> + struct dentry *rodd = olddir->i_private, *rndd = newdir->i_private,
> + *realold = old->d_inode->i_private,
> + *realnew = new->d_inode->i_private;
> + struct inode *realolddir = rodd->d_inode, *realnewdir = rndd->d_inode;
> + const struct inode_operations *iop = realolddir->i_op;
> + int err;
> + const struct cred *oldcred, *newcred;
> +
> + oldcred = shiftfs_new_creds(&newcred, old->d_sb);
> + err = iop->rename2(realolddir, realold, realnewdir, realnew, flags);
> + shiftfs_old_creds(oldcred, &newcred);
... and you've just violated all locking rules for ->rename2().
> +static struct dentry *shiftfs_lookup(struct inode *dir, struct dentry
> *dentry,
> + unsigned int flags)
> +{
> + struct dentry *real = dir->i_private, *new;
> + struct inode *reali = real->d_inode, *newi;
> + const struct cred *oldcred, *newcred;
> +
> + /* note: violation of usual fs rules here: dentries are never
> + * added with d_add. This is because we want no dentry cache
> + * for shiftfs. All lookups proceed through the dentry cache
> + * of the underlying filesystem, meaning we always see any
> + * changes in the underlying */
Bloody wonderful. So
* we lose caching the negative lookups
* we've got buggered hardlinks (different inodes for those)
* it has never, ever been tried on -next (would do rather nasty
things on that d_instantiate())
> +
> + kfree(sfc);
> +
> + return err;
> +}
> + file->f_op = &sfc->fop;
Lovely - now try that with underlying fs something built modular.
Or try to use it on top of something with non-trivial dentry_operations
(hell, on top of itself, for starters).
