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Message-ID: <CA+khW7ggTFp8je0zwo83uGN8pKZXy+D07y+tPRRAXmY+e3pm-g@mail.gmail.com>
Date: Wed, 3 Aug 2022 17:29:53 -0700
From: Hao Luo <haoluo@...gle.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Yosry Ahmed <yosryahmed@...gle.com>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
Johannes Weiner <hannes@...xchg.org>,
Shuah Khan <shuah@...nel.org>,
Michal Hocko <mhocko@...nel.org>,
KP Singh <kpsingh@...nel.org>,
Benjamin Tissoires <benjamin.tissoires@...hat.com>,
John Fastabend <john.fastabend@...il.com>,
Michal Koutný <mkoutny@...e.com>,
Roman Gushchin <roman.gushchin@...ux.dev>,
David Rientjes <rientjes@...gle.com>,
Stanislav Fomichev <sdf@...gle.com>,
Greg Thelen <gthelen@...gle.com>,
Shakeel Butt <shakeelb@...gle.com>,
linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
bpf@...r.kernel.org, cgroups@...r.kernel.org,
Kui-Feng Lee <kuifeng@...com>
Subject: Re: [PATCH bpf-next v5 4/8] bpf: Introduce cgroup iter
On Wed, Aug 3, 2022 at 1:40 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Wed, Aug 3, 2022 at 1:30 PM Hao Luo <haoluo@...gle.com> wrote:
> >
> > On Tue, Aug 2, 2022 at 3:50 PM Andrii Nakryiko
> > <andrii.nakryiko@...il.com> wrote:
> > >
> > > On Tue, Aug 2, 2022 at 3:27 PM Hao Luo <haoluo@...gle.com> wrote:
> > > >
> > > > On Mon, Aug 1, 2022 at 8:43 PM Andrii Nakryiko
> > > > <andrii.nakryiko@...il.com> wrote:
> > > > >
> > > > > On Fri, Jul 22, 2022 at 10:48 AM Yosry Ahmed <yosryahmed@...gle.com> wrote:
[...]
> > > > > > +};
> > > > > > +
> > > > > > union bpf_iter_link_info {
> > > > > > struct {
> > > > > > __u32 map_fd;
> > > > > > } map;
> > > > > > +
> > > > > > + /* cgroup_iter walks either the live descendants of a cgroup subtree, or the
> > > > > > + * ancestors of a given cgroup.
> > > > > > + */
> > > > > > + struct {
> > > > > > + /* Cgroup file descriptor. This is root of the subtree if walking
> > > > > > + * descendants; it's the starting cgroup if walking the ancestors.
> > > > > > + * If it is left 0, the traversal starts from the default cgroup v2
> > > > > > + * root. For walking v1 hierarchy, one should always explicitly
> > > > > > + * specify the cgroup_fd.
> > > > > > + */
> > > > > > + __u32 cgroup_fd;
> > > > >
> > > > > Now, similar to what I argued in regard of pidfd vs pid, I think the
> > > > > same applied to cgroup_fd vs cgroup_id. Why can't we support both?
> > > > > cgroup_fd has some benefits, but cgroup_id is nice due to simplicity
> > > > > and not having to open/close/keep extra FDs (which can add up if we
> > > > > want to periodically query something about a large set of cgroups).
> > > > > Please see my arguments from [0] above.
> > > > >
> > > > > Thoughts?
> > > > >
> > > >
> > > > We can support both, it's a good idea IMO. But what exactly is the
> > > > interface going to look like? Can you be more specific about that?
> > > > Below is something I tried based on your description.
> > > >
> > > > @@ -91,6 +91,18 @@ union bpf_iter_link_info {
> > > > struct {
> > > > __u32 map_fd;
> > > > } map;
> > > > + struct {
> > > > + /* PRE/POST/UP/SELF */
> > > > + __u32 order;
> > > > + struct {
> > > > + __u32 cgroup_fd;
> > > > + __u64 cgroup_id;
> > > > + } cgroup;
> > > > + struct {
> > > > + __u32 pid_fd;
> > > > + __u64 pid;
> > > > + } task;
> > > > + };
> > > > };
> > > >
> > >
> > > So I wouldn't combine task and cgroup definition together, let's keep
> > > them independent.
> > >
> > > then for cgroup we can do something like:
> > >
> > > struct {
> > > __u32 order;
> > > __u32 cgroup_fd; /* cgroup_fd ^ cgroup_id, exactly one can be non-zero */
> > > __u32 cgroup_id;
> > > } cgroup
> > >
> > > Similar idea with task, but it's a bit more complicated because there
> > > we have target that can be pid, pidfd, or cgroup (cgroup_fd and
> > > cgroup_id). I haven't put much thought into the best representation,
> > > though.
> > >
> >
> > The cgroup part sounds good to me. For the full picture, how about
> > this? I'm just trying a prototype, hoping that it can help people to
> > get a clear picture.
> >
> > union bpf_iter_link_info {
> > struct {
> > __u32 map_fd;
> > } map;
> > struct {
> > __u32 order; /* PRE/POST/UP/SELF */
> > __u32 cgroup_fd;
> > __u64 cgroup_id;
> > } cgroup;
>
> lgtm
>
> > struct {
> > __u32 pid;
> > __u32 pid_fd;
> > __u64 cgroup_id;
> > __u32 cgroup_fd;
> > __u32 mode; /* SELF or others */
>
> I'd move mode to be first. I'm undecided on using 4 separate fields
> for pid/pid_fd/cgroup_{id,fd} vs a single union (or just generic "u64
> target" and then mode can define how we should treat target --
> whether it's pid, pid_fd, cgroup ID or FD. I'm fine either way, I
> think. But for cgroup case not having to duplicate PRE/POST/UP/SELF
> for cgroup id and then for cgroup fd seems like a win. So separate
> fields might be better. It's also pretty extendable. And I'm
> personally not worried about using few more bytes in bpf_attr for
> disjoin fields like this.
>
Sounds good. Thanks for clarification. Using separate fields looks
good to me. Since we settled on the cgroup part, I will apply update
in cgroup_iter v7.
> > } task;
> > };
> >
> > > > > > + __u32 traversal_order;
> > > > > > + } cgroup;
> > > > > > };
> > > > > >
> > > > > > /* BPF syscall commands, see bpf(2) man-page for more details. */
> > > > >
> > > > > [...]
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