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Message-ID: <ZNVousfpuRFgfuAo@google.com>
Date: Thu, 10 Aug 2023 15:46:18 -0700
From: Stanislav Fomichev <sdf@...gle.com>
To: David Vernet <void@...ifault.com>
Cc: bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org,
yhs@...com, john.fastabend@...il.com, kpsingh@...nel.org,
haoluo@...gle.com, jolsa@...nel.org, linux-kernel@...r.kernel.org,
kernel-team@...a.com, tj@...nel.org, clm@...a.com,
thinker.li@...il.com
Subject: Re: [PATCH bpf-next] bpf: Support default .validate() and .update()
behavior for struct_ops links
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?
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