[PATCH V4] notifier/panic: Introduce panic_notifier_filter

[Baoquan He <bhe@redhat.com>]

On 01/08/22 at 12:34pm, Guilherme G. Piccoli wrote:
...... 
> So, this patch aims to ease this decision: we hereby introduce a filter
> for the panic notifier list, in which users may select specifically
> which callbacks they wish to run, allowing a safer kdump. The allowlist
> should be provided using the parameter "panic_notifier_filter=a,b,..."
> where a, b are valid callback names. Invalid symbols are discarded.
> 
> Currently up to 16 symbols may be passed in this list, we consider
> that this numbers allows enough flexibility (and no matter what
> architecture is used, at most 30 panic callbacks are registered).
> In an experiment using a qemu x86 virtual machine, by default only
> six callbacks are registered in the panic notifier list.
> Once a valid callback name is provided in the list, such function
> is allowed to be registered/unregistered in the panic_notifier_list;
> all other panic callbacks are ignored. Notice that this filter is
> only for the panic notifiers and has no effect in the other notifiers.
> 
> Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>

This patch looks good to me, thx.

Acked-by: Baoquan He <bhe@redhat.com>