Re: [PATCH bpf-next v1 7/8] libbpf: sync progs autoload with maps autocreate for struct_ops maps

[Kui-Feng Lee <sinquersw@gmail.com>]

On 2/27/24 15:30, Eduard Zingerman wrote:
> On Tue, 2024-02-27 at 15:16 -0800, Kui-Feng Lee wrote:
> [...]
> 
>>> So, it appears that with shadow types users would have more or less
>>> convenient way to disable / enable related BPF programs
>>> (the references to programs are available, but reference counting
>>>    would have to be implemented by user using some additional data
>>>    structure, if needed).
>>>
>>> I don't see a way to reconcile shadow types with this autoload/autocreate toggling
>>> => my last two patches would have to be dropped.
>>
>> How about to update autoload according to the value of autocreate of
>> maps before loading the programs? For example, update autoload in
>> bpf_map__init_kern_struct_ops()?
> 
> This can be done, but it would have to be a separate pass:
> first scanning all maps and setting up reference counters for programs,
> then scanning all programs and disabling those unused.
> I can do that in v2, thank you for the suggestion.
> 

It only has to scan once with an additional flag.
The value of the autoload of a prog should be
true if its autoload_user_set is false and autocreate of any one of
struct_ops maps pointing to the prog is true.

Let's say the flag is autoload_autocreate.
In bpf_map__init_kern_struct_ops(), it has to check
prog->autoload_user_set, and do prog->autoload |= map->autocreate if
prog->autoload_user_set is false and autoload_autocreate is true. Do 
prog->autoload = map->autocreate if autoload_autocreate is false I think 
it is enough, right?

if (!prog->autoload_user_set) {
     if (!prog->autoload_autocreate)
         prog->autoload = map->autocreate;
     else
         prog->autoload |= map->autocreate;
     prog->autoload_autocreate = true;
}