Re: [PATCH bpf] bpftool: Fix regression of "bpftool cgroup tree" EINVAL on older kernels

[Quentin Monnet <qmo@kernel.org>]

2025-04-28 21:15 UTC+0000 ~ YiFei Zhu <zhuyifei@google.com>
> If cgroup_has_attached_progs queries an attach type not supported
> by the running kernel, due to the kernel being older than the bpftool
> build, it would encounter an -EINVAL from BPF_PROG_QUERY syscall.
> 
> Prior to commit 98b303c9bf05 ("bpftool: Query only cgroup-related
> attach types"), this EINVAL would be ignored by the function, allowing
> the function to only consider supported attach types. The commit
> changed so that, instead of querying all attach types, only attach
> types from the array `cgroup_attach_types` is queried. The assumption
> is that because these are only cgroup attach types, they should all
> be supported. Unfortunately this assumption may be false when the
> kernel is older than the bpftool build, where the attach types queried
> by bpftool is not yet implemented in the kernel. This would result in
> errors such as:
> 
>   $ bpftool cgroup tree
>   CgroupPath
>   ID       AttachType      AttachFlags     Name
>   Error: can't query bpf programs attached to /sys/fs/cgroup: Invalid argument
> 
> This patch restores the logic of ignoring EINVAL from prior to that patch.
> 
> Fixes: 98b303c9bf05 ("bpftool: Query only cgroup-related attach types")
> Reported-by: Sagarika Sharma <sharmasagarika@google.com>
> Reported-by: Minh-Anh Nguyen <minhanhdn@google.com>
> Signed-off-by: YiFei Zhu <zhuyifei@google.com>


Acked-by: Quentin Monnet <qmo@kernel.org>

Thank you!