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SubjectRe: [PATCH 09/23] ns: Introduce ns_idr to be able to iterate all allocated namespaces in the system
On Thu, Jul 30, 2020 at 03:00:08PM +0300, Kirill Tkhai wrote:
> This patch introduces a new IDR and functions to add/remove and iterate
> registered namespaces in the system. It will be used to list namespaces
> in /proc/namespaces/... in next patches.

Looks like you could use an XArray for this and it would be fewer lines of
code.

>
> static struct vfsmount *nsfs_mnt;
> +static DEFINE_SPINLOCK(ns_lock);
> +static DEFINE_IDR(ns_idr);

XArray includes its own spinlock.

> +/*
> + * Add a newly created ns to ns_idr. The ns must be fully
> + * initialized since it becomes available for ns_get_next()
> + * right after we exit this function.
> + */
> +int ns_idr_register(struct ns_common *ns)
> +{
> + int ret, id = ns->inum - PROC_NS_MIN_INO;
> +
> + if (WARN_ON(id < 0))
> + return -EINVAL;
> +
> + idr_preload(GFP_KERNEL);
> + spin_lock_irq(&ns_lock);
> + ret = idr_alloc(&ns_idr, ns, id, id + 1, GFP_ATOMIC);
> + spin_unlock_irq(&ns_lock);
> + idr_preload_end();
> + return ret < 0 ? ret : 0;

This would simply be return xa_insert_irq(...);

> +}
> +
> +/*
> + * Remove a dead ns from ns_idr. Note, that ns memory must
> + * be freed not earlier then one RCU grace period after
> + * this function, since ns_get_next() uses RCU to iterate the IDR.
> + */
> +void ns_idr_unregister(struct ns_common *ns)
> +{
> + int id = ns->inum - PROC_NS_MIN_INO;
> + unsigned long flags;
> +
> + if (WARN_ON(id < 0))
> + return;
> +
> + spin_lock_irqsave(&ns_lock, flags);
> + idr_remove(&ns_idr, id);
> + spin_unlock_irqrestore(&ns_lock, flags);
> +}

xa_erase_irqsave();

> +
> +/*
> + * This returns ns with inum greater than @id or NULL.
> + * @id is updated to refer the ns inum.
> + */
> +struct ns_common *ns_get_next(unsigned int *id)
> +{
> + struct ns_common *ns;
> +
> + if (*id < PROC_NS_MIN_INO - 1)
> + *id = PROC_NS_MIN_INO - 1;
> +
> + *id += 1;
> + *id -= PROC_NS_MIN_INO;
> +
> + rcu_read_lock();
> + do {
> + ns = idr_get_next(&ns_idr, id);
> + if (!ns)
> + break;

xa_find_after();

You'll want a temporary unsigned long to work with ...

> + if (!refcount_inc_not_zero(&ns->count)) {
> + ns = NULL;
> + *id += 1;

you won't need this increment.

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