Re: [RFC v14-rc2][PATCH 1/7] ipc: allow allocation of an ipc object with desired identifier

["Serge E. Hallyn" <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

Quoting Oren Laadan (orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org):
> -int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
> +int
> +ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int size, int req_id)
>  {
>  	uid_t euid;
>  	gid_t egid;
> +	int lid = 0;
>  	int id, err;
> 
>  	if (size > IPCMNI)
> @@ -268,28 +270,41 @@ int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
>  	if (ids->in_use >= size)
>  		return -ENOSPC;
> 
> +	if (req_id >= 0)
> +		lid = ipcid_to_idx(req_id);
> +
>  	spin_lock_init(&new->lock);
>  	new->deleted = 0;
>  	rcu_read_lock();
>  	spin_lock(&new->lock);
> 
> -	err = idr_get_new(&ids->ipcs_idr, new, &id);
> +	err = idr_get_new_above(&ids->ipcs_idr, new, lid, &id);
>  	if (err) {
>  		spin_unlock(&new->lock);
>  		rcu_read_unlock();
>  		return err;
>  	}
> 
> +	if (req_id >= 0) {
> +		if (id != lid) {
> +			idr_remove(&ids->ipcs_idr, id);
> +			spin_unlock(&new->lock);
> +			rcu_read_unlock();
> +			return -EBUSY;
> +		}
> +		new->seq = req_id / SEQ_MULTIPLIER;

Should this be
	
	new->seq = req_id % ids->seq_max;

?

> +	} else {
> +		new->seq = ids->seq++;
> +		if (ids->seq > ids->seq_max)
> +			ids->seq = 0;
> +	}
> +
>  	ids->in_use++;
> 
>  	current_euid_egid(&euid, &egid);
>  	new->cuid = new->uid = euid;
>  	new->gid = new->cgid = egid;
> 
> -	new->seq = ids->seq++;
> -	if(ids->seq > ids->seq_max)
> -		ids->seq = 0;
> -