Re: [PATCH 1/7] shared subtree

[Miklos Szeredi <miklos@szeredi.hu>]

> > This is an example, where having struct pnode just complicates things.
> > If there was no struct pnode, this function would be just one line:
> > setting the shared flag.
> So your comment is mostly about getting rid of pnode and distributing
> the pnode functionality in the vfsmount structure.

Yes, sorry if I didn't make it clear.

> I know you are thinking of just having the necessary propogation list in
> the vfsmount structure itself.  Yes true with that implementation the
> complication is reduced in this part of the code, but really complicates
> the propogation traversal routines. 

On the contrary, I think it will simplify the traversal routines.

Here's an iterator function I coded up.  Not tested at all (may not
even compile):

struct vfsmount {
	/* ... */
        
	struct list_head mnt_share;      /* circular list of shared mounts */
	struct list_head mnt_slave_list; /* list of slave mounts */
	struct list_head mnt_slave;      /* slave list entry */
	struct vfsmount *master;         /* slave is on master->mnt_slave_list */
};

static inline struct vfsmount *next_shared(struct vfsmount *p)
{
	return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
}

static inline struct vfsmount *first_slave(struct vfsmount *p)
{
	return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave);
}

static inline struct vfsmount *next_slave(struct vfsmount *p)
{
	return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave);
}

static struct vfsmount *propagation_next(struct vfsmount *p,
					 struct vfsmount *base)
{
	/* first iterate over the slaves */
	if (!list_empty(&p->mnt_slave_list))
		return first_slave(p);

	while (1) {
		struct vfsmount *q;

		/* more vfsmounts belong to the pnode? */
		if (!list_empty(&p->mnt_share)) {
			p = next_shared(p);
			if (list_empty(&p->mnt_slave) && p != base)
				return p;
		}
		if (p == base)
			break;
		
		BUG_ON(list_empty(&p->mnt_slave));

		/* more slaves? */
		q = next_slave(p);
		if (p->master != q)
			return q;

		/* back at master */
		p = q;
	}

	return NULL;
}

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