Re: [PATCH bpf-next v3 2/3] libbpf: add low level TC-BPF API

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

On Wed, Apr 21, 2021 at 12:28:01PM IST, Yonghong Song wrote:
>
>
> On 4/20/21 12:37 PM, Kumar Kartikeya Dwivedi wrote:
> > This adds functions that wrap the netlink API used for adding,
> > manipulating, and removing traffic control filters. These functions
> > operate directly on the loaded prog's fd, and return a handle to the
> > filter using an out parameter named id.
> >
> > The basic featureset is covered to allow for attaching and removal of
> > filters. Some additional features like TCA_BPF_POLICE and TCA_RATE for
> > the API have been omitted. These can added on top later by extending the
>
> "later" => "layer"?
>

No, I meant that other options can be added on top of this series by someone
later. I'll reword it.

> > bpf_tc_opts struct.
> >
> > Support for binding actions directly to a classifier by passing them in
> > during filter creation has also been omitted for now. These actions have
> > an auto clean up property because their lifetime is bound to the filter
> > they are attached to. This can be added later, but was omitted for now
> > as direct action mode is a better alternative to it, which is enabled by
> > default.
> >
> > An API summary:
> >
> > bpf_tc_attach may be used to attach, and replace SCHED_CLS bpf
> > classifier. The protocol is always set as ETH_P_ALL. The replace option
> > in bpf_tc_opts is used to control replacement behavior.  Attachment
> > fails if filter with existing attributes already exists.
> >
> > bpf_tc_detach may be used to detach existing SCHED_CLS filter. The
> > bpf_tc_attach_id object filled in during attach must be passed in to the
> > detach functions for them to remove the filter and its attached
> > classififer correctly.
> >
> > bpf_tc_get_info is a helper that can be used to obtain attributes
> > for the filter and classififer.
> >
> > Examples:
> >
> > 	struct bpf_tc_attach_id id = {};
> > 	struct bpf_object *obj;
> > 	struct bpf_program *p;
> > 	int fd, r;
> >
> > 	obj = bpf_object_open("foo.o");
> > 	if (IS_ERR_OR_NULL(obj))
> > 		return PTR_ERR(obj);
> >
> > 	p = bpf_object__find_program_by_title(obj, "classifier");
>
> Please use bpf_object__find_program_by_name() API.
> bpf_object__find_program_by_title() is not recommended as now
> libbpf supports multiple programs within the same section.

Thanks, will do.

>
> > 	if (IS_ERR_OR_NULL(p))
> > 		return PTR_ERR(p);
> >
> > 	if (bpf_object__load(obj) < 0)
> > 		return -1;
> >
> > 	fd = bpf_program__fd(p);
> >
> > 	r = bpf_tc_attach(fd, if_nametoindex("lo"),
> > 			  BPF_TC_CLSACT_INGRESS,
> > 			  NULL, &id);
> > 	if (r < 0)
> > 		return r;
> >
> > ... which is roughly equivalent to:
> >    # tc qdisc add dev lo clsact
> >    # tc filter add dev lo ingress bpf obj foo.o sec classifier da
> >
> > ... as direct action mode is always enabled.
> >
> > To replace an existing filter:
> >
> > 	DECLARE_LIBBPF_OPTS(bpf_tc_opts, opts, .handle = id.handle,
> > 			    .priority = id.priority, .replace = true);
> > 	r = bpf_tc_attach(fd, if_nametoindex("lo"),
> > 			  BPF_TC_CLSACT_INGRESS,
> > 			  &opts, &id);
> > 	if (r < 0)
> > 		return r;
> >
> > To obtain info of a particular filter, the example above can be extended
> > as follows:
> >
> > 	struct bpf_tc_info info = {};
> >
> > 	r = bpf_tc_get_info(if_nametoindex("lo"),
> > 			    BPF_TC_CLSACT_INGRESS,
> > 			    &id, &info);
> > 	if (r < 0)
> > 		return r;
> >
> > ... where id corresponds to the bpf_tc_attach_id filled in during an
> > attach operation.
> >
> > Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
> > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> > ---
> >   tools/lib/bpf/libbpf.h   |  44 ++++++
> >   tools/lib/bpf/libbpf.map |   3 +
> >   tools/lib/bpf/netlink.c  | 319 ++++++++++++++++++++++++++++++++++++++-
> >   3 files changed, 360 insertions(+), 6 deletions(-)
> >
> > diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> > index bec4e6a6e31d..b4ed6a41ea70 100644
> > --- a/tools/lib/bpf/libbpf.h
> > +++ b/tools/lib/bpf/libbpf.h
> > @@ -16,6 +16,8 @@
> >   #include <stdbool.h>
> >   #include <sys/types.h>  // for size_t
> >   #include <linux/bpf.h>
> > +#include <linux/pkt_sched.h>
> > +#include <linux/tc_act/tc_bpf.h>
> >   #include "libbpf_common.h"
> > @@ -775,6 +777,48 @@ LIBBPF_API int bpf_linker__add_file(struct bpf_linker *linker, const char *filen
> >   LIBBPF_API int bpf_linker__finalize(struct bpf_linker *linker);
> >   LIBBPF_API void bpf_linker__free(struct bpf_linker *linker);
> > +/* Convenience macros for the clsact attach hooks */
> > +#define BPF_TC_CLSACT_INGRESS TC_H_MAKE(TC_H_CLSACT, TC_H_MIN_INGRESS)
> > +#define BPF_TC_CLSACT_EGRESS TC_H_MAKE(TC_H_CLSACT, TC_H_MIN_EGRESS)
> > +
> > +struct bpf_tc_opts {
> > +	size_t sz;
> > +	__u32 handle;
> > +	__u32 class_id;
> > +	__u16 priority;
> > +	bool replace;
> > +	size_t :0;
>
> Did you see any error without "size_t :0"?
>

Not really, I just added this considering this recent change:
dde7b3f5f2f4 ("libbpf: Add explicit padding to bpf_xdp_set_link_opts")

> > +};
> > +
> > +#define bpf_tc_opts__last_field replace
> > +
> > +/* Acts as a handle for an attached filter */
> > +struct bpf_tc_attach_id {
> > +	__u32 handle;
> > +	__u16 priority;
> > +};
> > +
> [...]

--
Kartikeya