[PATCH] rcu: add deprecation notice about limit on defer queue element size

[Andre Muezerie]

On Tue, Jul 01, 2025 at 04:17:20PM +0200, Thomas Monjalon wrote:
> 23/05/2025 01:37, Andre Muezerie:
> > The functions rte_rcu_qsbr_dq_create and rte_rcu_qsbr_dq_reclaim establish
> > no limit on the size of each element in the defer queue.
> 
> Very good, we need more unlimited API in DPDK.
> 
> > With DPDK 25.11 a hard limit will be set (``RTE_QSBR_ESIZE_MAX``).
> 
> I think it is a step in the wrong direction.
> I prefer having no limit.
> 
> > This will allow fixed C arrays to be used in the functions' implementations,
> > avoiding VLAs and use of alloca().
> 
> I don't understand this justification.
> Why trying to remove the 2 alloca() in the lib RCU?
> 

Only because other developer expressed concerns that using alloca() allows
ill-intended callers to cause a stack overflow.
I personally also prefer to have no hardcoded limits.