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Date:   Thu, 10 Aug 2023 15:46:18 -0700
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Subject: Re: [PATCH bpf-next] bpf: Support default .validate() and .update()
 behavior for struct_ops links
From:   Stanislav Fomichev <sdf@google.com>
To:     David Vernet <void@manifault.com>
Cc:     bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
        andrii@kernel.org, martin.lau@linux.dev, song@kernel.org,
        yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org,
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        kernel-team@meta.com, tj@kernel.org, clm@meta.com,
        thinker.li@gmail.com
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On 08/10, David Vernet wrote:
> Currently, if a struct_ops map is loaded with BPF_F_LINK, it must also
> define the .validate() and .update() callbacks in its corresponding
> struct bpf_struct_ops in the kernel. Enabling struct_ops link is useful
> in its own right to ensure that the map is unloaded if an application
> crashes. For example, with sched_ext, we want to automatically unload
> the host-wide scheduler if the application crashes. We would likely
> never support updating elements of a sched_ext struct_ops map, so we'd
> have to implement these callbacks showing that they _can't_ support
> element updates just to benefit from the basic lifetime management of
> struct_ops links.
> 
> Let's enable struct_ops maps to work with BPF_F_LINK even if they
> haven't defined these callbacks, by assuming that a struct_ops map
> element cannot be updated by default.

Any reason this is not part of sched_ext series? As you mention,
we don't seem to have such users in the three?