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Message-ID: <CAEf4BzbuD+vLzxVkXpiX=yKu2WbHLrekrZS8hx2TWU04m0h-kA@mail.gmail.com>
Date: Mon, 15 Aug 2022 21:17:09 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Hao Luo <haoluo@...gle.com>
Cc: linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
cgroups@...r.kernel.org, netdev@...r.kernel.org,
Alexei Starovoitov <ast@...nel.org>,
Andrii Nakryiko <andrii@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Martin KaFai Lau <martin.lau@...ux.dev>,
Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
KP Singh <kpsingh@...nel.org>,
Johannes Weiner <hannes@...xchg.org>,
Michal Hocko <mhocko@...nel.org>,
John Fastabend <john.fastabend@...il.com>,
Michal Koutny <mkoutny@...e.com>,
Roman Gushchin <roman.gushchin@...ux.dev>,
David Rientjes <rientjes@...gle.com>,
Stanislav Fomichev <sdf@...gle.com>,
Shakeel Butt <shakeelb@...gle.com>,
Yosry Ahmed <yosryahmed@...gle.com>
Subject: Re: [PATCH bpf-next v8 1/5] bpf: Introduce cgroup iter
On Fri, Aug 12, 2022 at 1:28 PM Hao Luo <haoluo@...gle.com> wrote:
>
> Cgroup_iter is a type of bpf_iter. It walks over cgroups in four modes:
>
> - walking a cgroup's descendants in pre-order.
> - walking a cgroup's descendants in post-order.
> - walking a cgroup's ancestors.
> - process only the given cgroup.
>
> When attaching cgroup_iter, one can set a cgroup to the iter_link
> created from attaching. This cgroup is passed as a file descriptor
> or cgroup id and serves as the starting point of the walk. If no
> cgroup is specified, the starting point will be the root cgroup v2.
>
> For walking descendants, one can specify the order: either pre-order or
> post-order. For walking ancestors, the walk starts at the specified
> cgroup and ends at the root.
>
> One can also terminate the walk early by returning 1 from the iter
> program.
>
> Note that because walking cgroup hierarchy holds cgroup_mutex, the iter
> program is called with cgroup_mutex held.
>
> Currently only one session is supported, which means, depending on the
> volume of data bpf program intends to send to user space, the number
> of cgroups that can be walked is limited. For example, given the current
> buffer size is 8 * PAGE_SIZE, if the program sends 64B data for each
> cgroup, assuming PAGE_SIZE is 4kb, the total number of cgroups that can
> be walked is 512. This is a limitation of cgroup_iter. If the output
> data is larger than the kernel buffer size, after all data in the
> kernel buffer is consumed by user space, the subsequent read() syscall
> will signal EOPNOTSUPP. In order to work around, the user may have to
> update their program to reduce the volume of data sent to output. For
> example, skip some uninteresting cgroups. In future, we may extend
> bpf_iter flags to allow customizing buffer size.
>
> Acked-by: Yonghong Song <yhs@...com>
> Acked-by: Tejun Heo <tj@...nel.org>
> Signed-off-by: Hao Luo <haoluo@...gle.com>
> ---
> include/linux/bpf.h | 8 +
> include/uapi/linux/bpf.h | 35 +++
> kernel/bpf/Makefile | 3 +
> kernel/bpf/cgroup_iter.c | 283 ++++++++++++++++++
> tools/include/uapi/linux/bpf.h | 35 +++
> .../selftests/bpf/prog_tests/btf_dump.c | 4 +-
> 6 files changed, 366 insertions(+), 2 deletions(-)
> create mode 100644 kernel/bpf/cgroup_iter.c
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index a627a02cf8ab..ecb8c61178a1 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -48,6 +48,7 @@ struct mem_cgroup;
> struct module;
> struct bpf_func_state;
> struct ftrace_ops;
> +struct cgroup;
>
> extern struct idr btf_idr;
> extern spinlock_t btf_idr_lock;
> @@ -1730,7 +1731,14 @@ int bpf_obj_get_user(const char __user *pathname, int flags);
> int __init bpf_iter_ ## target(args) { return 0; }
>
> struct bpf_iter_aux_info {
> + /* for map_elem iter */
> struct bpf_map *map;
> +
> + /* for cgroup iter */
> + struct {
> + struct cgroup *start; /* starting cgroup */
> + int order;
why not using enum as a type here?
> + } cgroup;
> };
>
> typedef int (*bpf_iter_attach_target_t)(struct bpf_prog *prog,
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 7d1e2794d83e..bc3c901b9f70 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -87,10 +87,34 @@ struct bpf_cgroup_storage_key {
> __u32 attach_type; /* program attach type (enum bpf_attach_type) */
> };
>
> +enum bpf_iter_order {
> + BPF_ITER_DESCENDANTS_PRE = 0, /* walk descendants in pre-order. */
> + BPF_ITER_DESCENDANTS_POST, /* walk descendants in post-order. */
> + BPF_ITER_ANCESTORS_UP, /* walk ancestors upward. */
> + BPF_ITER_SELF_ONLY, /* process only a single object. */
> +};
> +
> union bpf_iter_link_info {
> struct {
> __u32 map_fd;
> } map;
> + struct {
> + /* Users must specify order using one of the following values:
> + * - BPF_ITER_DESCENDANTS_PRE
> + * - BPF_ITER_DESCENDANTS_POST
> + * - BPF_ITER_ANCESTORS_UP
> + * - BPF_ITER_SELF_ONLY
> + */
> + __u32 order;
same, we just declared the UAPI enum above, why not specify that this
is that enum here?
> +
> + /* At most one of cgroup_fd and cgroup_id can be non-zero. If
> + * both are zero, the walk starts from the default cgroup v2
> + * root. For walking v1 hierarchy, one should always explicitly
> + * specify cgroup_fd.
> + */
> + __u32 cgroup_fd;
> + __u64 cgroup_id;
for my own education, does root cgroup has cgroup_id == 0?
> + } cgroup;
> };
>
[...]
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