On Tue, Jan 23, 2024 at 11:27:14PM +0800, Yafang Shao wrote:
> Add three new kfuncs for bpf_iter_cpumask.
> - bpf_iter_cpumask_new
> KF_RCU is defined because the cpumask must be a RCU trusted pointer
> such as task->cpus_ptr.
> - bpf_iter_cpumask_next
> - bpf_iter_cpumask_destroy
>
> These new kfuncs facilitate the iteration of percpu data, such as
> runqueues, psi_cgroup_cpu, and more.
>
> Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
Thanks for working on this, this will be nice to have!
> ---
> kernel/bpf/cpumask.c | 82 ++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 82 insertions(+)
>
> diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c
> index 2e73533a3811..474072a235d6 100644
> --- a/kernel/bpf/cpumask.c
> +++ b/kernel/bpf/cpumask.c
> @@ -422,6 +422,85 @@ __bpf_kfunc u32 bpf_cpumask_weight(const struct cpumask *cpumask)
> return cpumask_weight(cpumask);
> }
>
> +struct bpf_iter_cpumask {
> + __u64 __opaque[2];
> +} __aligned(8);
> +
> +struct bpf_iter_cpumask_kern {
> + struct cpumask *mask;
> + int cpu;
> +} __aligned(8);
Why do we need both of these if we're not going to put the opaque
iterator in UAPI?
> +
> +/**
> + * bpf_iter_cpumask_new() - Create a new bpf_iter_cpumask for a specified cpumask
> + * @it: The new bpf_iter_cpumask to be created.
> + * @mask: The cpumask to be iterated over.
> + *
> + * This function initializes a new bpf_iter_cpumask structure for iterating over
> + * the specified CPU mask. It assigns the provided cpumask to the newly created
> + * bpf_iter_cpumask @it for subsequent iteration operations.
> + *
> + * On success, 0 is returen. On failure, ERR is returned.
> + */
> +__bpf_kfunc int bpf_iter_cpumask_new(struct bpf_iter_cpumask *it, const struct cpumask *mask)
> +{
> + struct bpf_iter_cpumask_kern *kit = (void *)it;
> +
> + BUILD_BUG_ON(sizeof(struct bpf_iter_cpumask_kern) > sizeof(struct bpf_iter_cpumask));
> + BUILD_BUG_ON(__alignof__(struct bpf_iter_cpumask_kern) !=
> + __alignof__(struct bpf_iter_cpumask));
Why are we checking > in the first expression instead of just plain
equality?
> +
> + kit->mask = bpf_mem_alloc(&bpf_global_ma, sizeof(struct cpumask));
Probably better to use cpumask_size() here.
> + if (!kit->mask)
> + return -ENOMEM;
> +
> + cpumask_copy(kit->mask, mask);
> + kit->cpu = -1;
> + return 0;
> +}
> +
> +/**
> + * bpf_iter_cpumask_next() - Get the next CPU in a bpf_iter_cpumask
> + * @it: The bpf_iter_cpumask
> + *
> + * This function retrieves a pointer to the number of the next CPU within the
> + * specified bpf_iter_cpumask. It allows sequential access to CPUs within the
> + * cpumask. If there are no further CPUs available, it returns NULL.
> + *
> + * Returns a pointer to the number of the next CPU in the cpumask or NULL if no
> + * further CPUs.
> + */
> +__bpf_kfunc int *bpf_iter_cpumask_next(struct bpf_iter_cpumask *it)
> +{
> + struct bpf_iter_cpumask_kern *kit = (void *)it;
> + const struct cpumask *mask = kit->mask;
> + int cpu;
> +
> + if (!mask)
> + return NULL;
> + cpu = cpumask_next(kit->cpu, mask);
> + if (cpu >= nr_cpu_ids)
> + return NULL;
> +
> + kit->cpu = cpu;
> + return &kit->cpu;
> +}
> +
> +/**
> + * bpf_iter_cpumask_destroy() - Destroy a bpf_iter_cpumask
> + * @it: The bpf_iter_cpumask to be destroyed.
> + *
> + * Destroy the resource assiciated with the bpf_iter_cpumask.
> + */
> +__bpf_kfunc void bpf_iter_cpumask_destroy(struct bpf_iter_cpumask *it)
> +{
> + struct bpf_iter_cpumask_kern *kit = (void *)it;
> +
> + if (!kit->mask)
> + return;
> + bpf_mem_free(&bpf_global_ma, kit->mask);
> +}
> +
> __bpf_kfunc_end_defs();
>
> BTF_SET8_START(cpumask_kfunc_btf_ids)
> @@ -450,6 +529,9 @@ BTF_ID_FLAGS(func, bpf_cpumask_copy, KF_RCU)
> BTF_ID_FLAGS(func, bpf_cpumask_any_distribute, KF_RCU)
> BTF_ID_FLAGS(func, bpf_cpumask_any_and_distribute, KF_RCU)
> BTF_ID_FLAGS(func, bpf_cpumask_weight, KF_RCU)
> +BTF_ID_FLAGS(func, bpf_iter_cpumask_new, KF_ITER_NEW | KF_RCU)
> +BTF_ID_FLAGS(func, bpf_iter_cpumask_next, KF_ITER_NEXT | KF_RET_NULL)
> +BTF_ID_FLAGS(func, bpf_iter_cpumask_destroy, KF_ITER_DESTROY)
> BTF_SET8_END(cpumask_kfunc_btf_ids)
>
> static const struct btf_kfunc_id_set cpumask_kfunc_set = {
> --
> 2.39.1
>
>
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