Re: [PATCH bpf-next v5 2/3] libbpf: add low level TC-BPF API

Andrii Nakryiko
2021-04-30T19:35:54Z

On Wed, Apr 28, 2021 at 9:26 AM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> This adds functions that wrap the netlink API used for adding,
> manipulating, and removing traffic control filters.
>
> An API summary:
>
> A bpf_tc_hook represents a location where a TC-BPF filter can be
> attached. This means that creating a hook leads to creation of the
> backing qdisc, while destruction either removes all filters attached to
> a hook, or destroys qdisc if requested explicitly (as discussed below).
>
> The TC-BPF API functions operate on this bpf_tc_hook to attach, replace,
> query, and detach tc filters.
>
> All functions return 0 on success, and a negative error code on failure.
>
> bpf_tc_hook_create - Create a hook
> Parameters:
> @hook - Cannot be NULL, ifindex > 0, attach_point must be set to
> proper enum constant. Note that parent must be unset when
> attach_point is one of BPF_TC_INGRESS or BPF_TC_EGRESS. Note
> that as an exception BPF_TC_INGRESS|BPF_TC_EGRESS is also a
> valid value for attach_point.
>
> Returns -EOPNOTSUPP when hook has attach_point as BPF_TC_CUSTOM.
>
> @flags - Currently only BPF_TC_F_REPLACE, which creates qdisc in
> non-exclusive mode (i.e. an existing qdisc will be replaced
> instead of this function failing with -EEXIST).
>
> bpf_tc_hook_destroy - Destroy the hook
> Parameters:
> @hook - Cannot be NULL. The behaviour depends on value of
> attach_point.
>
> If BPF_TC_INGRESS, all filters attached to the ingress
> hook will be detached.
> If BPF_TC_EGRESS, all filters attached to the egress hook
> will be detached.
> If BPF_TC_INGRESS|BPF_TC_EGRESS, the clsact qdisc will be
> deleted, also detaching all filters.
>
> It is advised that if the qdisc is operated on by many programs,
> then the program atleast check that there are no other existing

typo: at least

> filters before deleting the clsact qdisc. An example is shown
> below:
>
> /* set opts as NULL, as we're not really interested in
> * getting any info for a particular filter, but just
> * detecting its presence.
> */

this comment probably is better moved to right before bpf_tc_query,
otherwise it reads as if it's related to bpf_tc_hook

> DECLARE_LIBBPF_OPTS(bpf_tc_hook, .ifindex = if_nametoindex("lo"),
> .attach_point = BPF_TC_INGRESS);
> r = bpf_tc_query(&hook, NULL);
> if (r < 0 && r == -ENOENT) {

well, r == -ENOENT should be enough then, no?

> /* no filters */
> hook.attach_point = BPF_TC_INGRESS|BPF_TC_EGREESS;
> return bpf_tc_hook_destroy(&hook);
> } else /* failed or r == 0, the latter means filters do exist */
> return r;
>
> Note that there is a small race between checking for no
> filters and deleting the qdisc. This is currently unavoidable.
>
> Returns -EOPNOTSUPP when hook has attach_point as BPF_TC_CUSTOM.
>
> bpf_tc_attach - Attach a filter to a hook
> Parameters:
> @hook - Cannot be NULL. Represents the hook the filter will be
> attached to. Requirements for ifindex and attach_point are
> same as described in bpf_tc_hook_create, but BPF_TC_CUSTOM
> is also supported. In that case, parent must be set to the
> handle where the filter will be attached (using TC_H_MAKE).
>
> E.g. To set parent to 1:16 like in tc command line,
> the equivalent would be TC_H_MAKE(1 << 16, 16)
>
> @opts - Cannot be NULL.
>
> The following opts are optional:
> handle - The handle of the filter
> priority - The priority of the filter
> Must be >= 0 and <= UINT16_MAX
> The following opts must be set:
> prog_fd - The fd of the loaded SCHED_CLS prog
> The following opts must be unset:
> prog_id - The ID of the BPF prog
>
> The following opts will be filled by bpf_tc_attach on a
> successful attach operation if they are unset:
> handle - The handle of the attached filter
> priority - The priority of the attached filter
> prog_id - The ID of the attached SCHED_CLS prog
>
> This way, the user can know what the auto allocated
> values for optional opts like handle and priority are
> for the newly attached filter, if they were unset.
>
> Note that some other attributes are set to some default
> values listed below (this holds for all bpf_tc_* APIs):
> protocol - ETH_P_ALL
> mode - direct action
> chain index - 0
> class ID - 0 (this can be set by writing to the
> skb->tc_classid field from the BPF program)
>
> @flags - Currently only BPF_TC_F_REPLACE, which creates filter
> in non-exclusive mode (i.e. an existing filter with the
> same attributes will be replaced instead of this
> function failing with -EEXIST).
>
> bpf_tc_detach
> Parameters:
> @hook: Cannot be NULL. Represents the hook the filter will be
> detached from. Requirements are same as described above
> in bpf_tc_attach.
>
> @opts: Cannot be NULL.
>
> The following opts must be set:
> handle
> priority
> The following opts must be unset:
> prog_fd
> prog_id
>
> bpf_tc_query
> Parameters:
> @hook: Cannot be NULL. Represents the hook where the filter
> lookup will be performed. Requires are same as described
> above in bpf_tc_attach.
>
> @opts: Can be NULL.
>
> The following opts are optional:
> handle
> priority
> prog_fd
> prog_id
>
> However, only one of prog_fd and prog_id must be
> set. Setting both leads to an error. Setting none is
> allowed.
>
> The following fields will be filled by bpf_tc_query on a
> successful lookup if they are unset:
> handle
> priority
> prog_id
>
> Based on the specified optional parameters, the matching
> data for the first matching filter is filled in and 0 is
> returned. When setting prog_fd, the prog_id will be
> matched against prog_id of the loaded SCHED_CLS prog
> represented by prog_fd.
>
> To uniquely identify a filter, e.g. to detect its presence,
> it is recommended to set both handle and priority fields.
>
> Some usage examples (using bpf skeleton infrastructure):
>
> BPF program (test_tc_bpf.c):
>
> #include <linux/bpf.h>
> #include <bpf/bpf_helpers.h>
>
> SEC("classifier")
> int cls(struct __sk_buff *skb)
> {
> return 0;
> }
>
> Userspace loader:
>
> DECLARE_LIBBPF_OPTS(bpf_tc_opts, opts, 0);
> struct test_tc_bpf *skel = NULL;
> int fd, r;
>
> skel = test_tc_bpf__open_and_load();
> if (!skel)
> return -ENOMEM;
>
> fd = bpf_program__fd(skel->progs.cls);
>
> DECLARE_LIBBPF_OPTS(bpf_tc_hook, hook, .ifindex =
> if_nametoindex("lo"), .attach_point =
> BPF_TC_INGRESS);
> /* Create clsact qdisc */
> r = bpf_tc_hook_create(&hook, 0);
> if (r < 0)
> goto end;
>
> DECLARE_LIBBPF_OPTS(bpf_tc_opts, opts, .prog_fd = fd);

I don't feel too strongly about this w.r.t. example, but
DECLARE_LIBBPF_OPTS() does declare a variable, so according to C89 all
such declarations should be gathered at the top. It would be nice to
stick to this in the example, but I can see how such locality is a bit
better for educational purposes, so I'm ok with that as well.

> r = bpf_tc_attach(&hook, &opts, 0);
> if (r < 0)
> goto end;
> /* Print the auto allocated handle and priority */
> printf("Handle=%"PRIu32", opts.handle);

let's drop PRIu32, libbpf doesn't use it so let's not use it as an
example, %u would work fine here

> printf("Priority=%"PRIu32", opts.priority);
>
> opts.prog_fd = opts.prog_id = 0;
> bpf_tc_detach(&hook, &opts);
> end:
> test_tc_bpf__destroy(skel);
>
> This is equivalent to doing the following using tc command line:
> # tc qdisc add dev lo clsact
> # tc filter add dev lo ingress bpf obj foo.o sec classifier da
>
> Another example replacing a filter (extending prior example):
>
> /* We can also choose both (or one), let's try replacing an
> * existing filter.
> */
> DECLARE_LIBBPF_OPTS(bpf_tc_opts, replace_opts, .handle =
> opts.handle, .priority = opts.priority,
> .prog_fd = fd);
> r = bpf_tc_attach(&hook, &replace_opts, 0);
> if (r < 0 && r == -EEXIST) {

again, == -EEXISTS implies r < 0, this just looks sloppy

> /* Expected, now use BPF_TC_F_REPLACE to replace it */
> return bpf_tc_attach(&hook, &replace_opts, BPF_TC_F_REPLACE);
> } else if (r == 0) {

I'd go with

else if (r < 0) {
return r;
}

/* handle happy case without unnecessary nesting */

> /* There must be no existing filter with these
> * attributes, so cleanup and return an error.
> */
> replace_opts.prog_fd = replace_opts.prog_id = 0;
> r = bpf_tc_detach(&hook, &replace_opts);
> if (r == 0)
> r = -1;

just return -1;

> }
> return r;
>
> To obtain info of a particular filter:
>
> /* Find info for filter with handle 1 and priority 50 */
> DECLARE_LIBBPF_OPTS(bpf_tc_opts, info_opts, .handle = 1,
> .priority = 50);
> r = bpf_tc_query(&hook, &info_opts);
> if (r < 0 && r == -ENOENT)
> printf("Filter not found");
> else if (r == 0)
> printf("Prog ID: %"PRIu32", info_opts.prog_id);

same about PRI and r < 0

> return r;
>
> We can also match using prog_id to find the same filter:
>
> DECLARE_LIBBPF_OPTS(bpf_tc_opts, info_opts2, .prog_id =
> info_opts.prog_id);
> r = bpf_tc_query(&hook, &info_opts2);
> if (r < 0 && r == -ENOENT)
> printf("Filter not found");
> else if (r == 0) {
> /* If we know there's only one filter for this loaded prog,
> * it is safe to assert that the handle and priority are
> * as expected.
> */
> assert(info_opts2.handle == 1);
> assert(info_opts2.priority == 50);
> }
> return r;
>
> Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---

API looks good to me (except the flags field that just stands out).
But I'll defer to Daniel to make the final call.

> tools/lib/bpf/libbpf.h | 41 ++++
> tools/lib/bpf/libbpf.map | 5 +
> tools/lib/bpf/netlink.c | 463 ++++++++++++++++++++++++++++++++++++++-
> 3 files changed, 508 insertions(+), 1 deletion(-)
>
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index bec4e6a6e31d..3de701f46a33 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -775,6 +775,47 @@ 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);
>
> +enum bpf_tc_attach_point {
> + BPF_TC_INGRESS = 1 << 0,
> + BPF_TC_EGRESS = 1 << 1,
> + BPF_TC_CUSTOM = 1 << 2,
> +};
> +
> +enum bpf_tc_attach_flags {
> + BPF_TC_F_REPLACE = 1 << 0,
> +};
> +
> +struct bpf_tc_hook {
> + size_t sz;
> + int ifindex;
> + enum bpf_tc_attach_point attach_point;
> + __u32 parent;
> + size_t :0;
> +};
> +
> +#define bpf_tc_hook__last_field parent
> +
> +struct bpf_tc_opts {
> + size_t sz;
> + int prog_fd;
> + __u32 prog_id;
> + __u32 handle;
> + __u32 priority;
> + size_t :0;
> +};
> +
> +#define bpf_tc_opts__last_field priority
> +
> +LIBBPF_API int bpf_tc_hook_create(struct bpf_tc_hook *hook, int flags);
> +LIBBPF_API int bpf_tc_hook_destroy(struct bpf_tc_hook *hook);
> +LIBBPF_API int bpf_tc_attach(const struct bpf_tc_hook *hook,
> + struct bpf_tc_opts *opts,
> + int flags);

why didn't you put flags into bpf_tc_opts? they are clearly optional
and fit into "opts" paradigm...

> +LIBBPF_API int bpf_tc_detach(const struct bpf_tc_hook *hook,
> + const struct bpf_tc_opts *opts);
> +LIBBPF_API int bpf_tc_query(const struct bpf_tc_hook *hook,
> + struct bpf_tc_opts *opts);
> +
> #ifdef __cplusplus
> } /* extern "C" */
> #endif
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index b9b29baf1df8..04509c7c144b 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -361,4 +361,9 @@ LIBBPF_0.4.0 {
> bpf_linker__new;
> bpf_map__inner_map;
> bpf_object__set_kversion;
> + bpf_tc_hook_create;
> + bpf_tc_hook_destroy;

please keep this alphabetically sorted

> + bpf_tc_attach;
> + bpf_tc_detach;
> + bpf_tc_query;
> } LIBBPF_0.3.0;
> diff --git a/tools/lib/bpf/netlink.c b/tools/lib/bpf/netlink.c
> index 6daee6640725..88f7b6144c78 100644
> --- a/tools/lib/bpf/netlink.c
> +++ b/tools/lib/bpf/netlink.c
> @@ -4,7 +4,11 @@
> #include <stdlib.h>
> #include <memory.h>
> #include <unistd.h>
> +#include <inttypes.h>
> +#include <arpa/inet.h>
> #include <linux/bpf.h>
> +#include <linux/if_ether.h>
> +#include <linux/pkt_cls.h>
> #include <linux/rtnetlink.h>
> #include <sys/socket.h>
> #include <errno.h>
> @@ -73,6 +77,12 @@ static int libbpf_netlink_open(__u32 *nl_pid)
> return ret;
> }
>
> +enum {
> + BPF_NL_CONT,
> + BPF_NL_NEXT,
> + BPF_NL_DONE,
> +};
> +
> static int bpf_netlink_recv(int sock, __u32 nl_pid, int seq,
> __dump_nlmsg_t _fn, libbpf_dump_nlmsg_t fn,
> void *cookie)
> @@ -84,6 +94,7 @@ static int bpf_netlink_recv(int sock, __u32 nl_pid, int seq,
> int len, ret;
>
> while (multipart) {
> +start:
> multipart = false;
> len = recv(sock, buf, sizeof(buf), 0);
> if (len < 0) {
> @@ -121,8 +132,18 @@ static int bpf_netlink_recv(int sock, __u32 nl_pid, int seq,
> }
> if (_fn) {
> ret = _fn(nh, fn, cookie);
> - if (ret)
> + if (ret < 0)
> + return ret;
> + switch (ret) {
> + case BPF_NL_CONT:
> + break;
> + case BPF_NL_NEXT:
> + goto start;
> + case BPF_NL_DONE:
> + return 0;
> + default:
> return ret;
> + }
> }
> }
> }
> @@ -357,3 +378,443 @@ static int libbpf_nl_send_recv(struct nlmsghdr *nh, __dump_nlmsg_t fn,
> close(sock);
> return ret;
> }
> +
> +/* TC-HOOK */
> +
> +typedef int (*qdisc_config_t)(struct nlmsghdr *nh, struct tcmsg *t,
> + size_t maxsz);
> +
> +static int clsact_config(struct nlmsghdr *nh, struct tcmsg *t, size_t maxsz)
> +{
> + int ret;
> +
> + t->tcm_parent = TC_H_CLSACT;
> + t->tcm_handle = TC_H_MAKE(TC_H_CLSACT, 0);
> +
> + ret = nlattr_add(nh, maxsz, TCA_KIND, "clsact", sizeof("clsact"));
> + if (ret < 0)
> + return ret;
> +
> + return 0;

nit: return nlattr_add(...)

> +}
> +
> +static int attach_point_to_config(struct bpf_tc_hook *hook, qdisc_config_t *configp)
> +{
> + if (!hook)
> + return -EINVAL;

!hook should be already ensured by calling functions, no need to
re-check this everywhere, do this only in API methods. All internal
functions should already ensure non-NULL, otherwise it's a bug.

> +
> + switch ((int)OPTS_GET(hook, attach_point, 0)) {

is int casting necessary here?

> + case BPF_TC_INGRESS:
> + case BPF_TC_EGRESS:
> + case BPF_TC_INGRESS|BPF_TC_EGRESS:
> + if (OPTS_GET(hook, parent, 0))
> + return -EINVAL;
> + *configp = &clsact_config;
> + break;
> + case BPF_TC_CUSTOM:
> + return -EOPNOTSUPP;
> + default:
> + return -EINVAL;
> + }
> +
> + return 0;
> +}
> +
> +static long long int tc_get_tcm_parent(enum bpf_tc_attach_point attach_point,
> + __u32 parent)
> +{
> + long long int ret;
> +
> + switch (attach_point) {
> + case BPF_TC_INGRESS:
> + if (parent)
> + return -EINVAL;
> + ret = TC_H_MAKE(TC_H_CLSACT, TC_H_MIN_INGRESS);

direct return

> + break;
> + case BPF_TC_EGRESS:
> + if (parent)
> + return -EINVAL;
> + ret = TC_H_MAKE(TC_H_CLSACT, TC_H_MIN_EGRESS);

same, make it explicit that we are done and it's the final value returned

> + break;
> + case BPF_TC_CUSTOM:
> + if (!parent)
> + return -EINVAL;
> + ret = parent;
> + break;
> + default:
> + return -EINVAL;
> + }
> +
> + return ret;
> +}
> +
> +static int tc_qdisc_modify(struct bpf_tc_hook *hook, int cmd, int flags)
> +{
> + qdisc_config_t config;
> + int ret = 0;

unnecessary initialization, some tooling definitely will complain,
please drop = 0 part

> + struct {
> + struct nlmsghdr nh;
> + struct tcmsg t;
> + char buf[256];
> + } req;
> +
> + ret = attach_point_to_config(hook, &config);
> + if (ret < 0)
> + return ret;
> +
> + memset(&req, 0, sizeof(req));
> + req.nh.nlmsg_len = NLMSG_LENGTH(sizeof(struct tcmsg));
> + req.nh.nlmsg_flags =
> + NLM_F_REQUEST | NLM_F_ACK | flags;

we can go up to 100 character lines, keep it on single line

> + req.nh.nlmsg_type = cmd;
> + req.t.tcm_family = AF_UNSPEC;
> + req.t.tcm_ifindex = OPTS_GET(hook, ifindex, 0);
> +
> + ret = config(&req.nh, &req.t, sizeof(req));
> + if (ret < 0)
> + return ret;
> +
> + ret = libbpf_nl_send_recv(&req.nh, NULL, NULL, NULL);
> + if (ret < 0)
> + return ret;
> +
> + return 0;
> +}
> +
> +static int tc_qdisc_create_excl(struct bpf_tc_hook *hook, int flags)
> +{
> + flags = flags & BPF_TC_F_REPLACE ? NLM_F_REPLACE : NLM_F_EXCL;

see below as well, please use () around bit operators

> + return tc_qdisc_modify(hook, RTM_NEWQDISC, NLM_F_CREATE | flags);
> +}
> +
> +static int tc_qdisc_delete(struct bpf_tc_hook *hook)
> +{
> + return tc_qdisc_modify(hook, RTM_DELQDISC, 0);
> +}
> +
> +int bpf_tc_hook_create(struct bpf_tc_hook *hook, int flags)
> +{
> + if (!hook || !OPTS_VALID(hook, bpf_tc_hook))
> + return -EINVAL;
> + if (OPTS_GET(hook, ifindex, 0) <= 0 || flags & ~BPF_TC_F_REPLACE)

please use () around bit operators

> + return -EINVAL;
> +
> + return tc_qdisc_create_excl(hook, flags);
> +}
> +
> +static int tc_cls_detach(const struct bpf_tc_hook *hook,
> + const struct bpf_tc_opts *opts, bool flush);
> +
> +int bpf_tc_hook_destroy(struct bpf_tc_hook *hook)
> +{
> + if (!hook || !OPTS_VALID(hook, bpf_tc_hook) ||
> + OPTS_GET(hook, ifindex, 0) <= 0)
> + return -EINVAL;
> +
> + switch ((int)OPTS_GET(hook, attach_point, 0)) {

int casting. Did the compiler complain about that or what?

> + case BPF_TC_INGRESS:
> + case BPF_TC_EGRESS:
> + return tc_cls_detach(hook, NULL, true);
> + case BPF_TC_INGRESS|BPF_TC_EGRESS:
> + return tc_qdisc_delete(hook);
> + case BPF_TC_CUSTOM:
> + return -EOPNOTSUPP;
> + default:
> + return -EINVAL;
> + }
> +}
> +
> +struct pass_info {
> + struct bpf_tc_opts *opts;
> + __u32 match_prog_id;
> + bool processed;
> +};
> +
> +/* TC-BPF */
> +
> +static int tc_cls_add_fd_and_name(struct nlmsghdr *nh, size_t maxsz, int fd)
> +{
> + struct bpf_prog_info info = {};
> + char name[256] = {};

you are unconditionally snprintf()'ing into name, don't unnecessarily
initialize it

> + int len, ret;
> +
> + ret = bpf_obj_get_info_by_fd(fd, &info, &(__u32){sizeof(info)});

that sizeof part... even if that works reliably, stick to normal use
pattern, have a local variable for that. It can be overwritten by the
kernel.

you can re-use len for this, btw

> + if (ret < 0)
> + return ret;
> +
> + ret = nlattr_add(nh, maxsz, TCA_BPF_FD, &fd, sizeof(fd));
> + if (ret < 0)
> + return ret;
> +
> + len = snprintf(name, sizeof(name), "%s:[%" PRIu32 "]", info.name,

libbpf doesn't use PRI modifiers, use %u

> + info.id);
> + if (len < 0 || len >= sizeof(name))
> + return len < 0 ? -EINVAL : -ENAMETOOLONG;

if (len < 0)
return -errno;
if (len >= sizeof(name))
return -ENAMETOOLONG;

> +
> + return nlattr_add(nh, maxsz, TCA_BPF_NAME, name, len + 1);
> +}
> +
> +
> +static int cls_get_info(struct nlmsghdr *nh, libbpf_dump_nlmsg_t fn,
> + void *cookie);
> +
> +int bpf_tc_attach(const struct bpf_tc_hook *hook,
> + struct bpf_tc_opts *opts, int flags)
> +{
> + __u32 protocol = 0, bpf_flags;
> + struct pass_info info = {};
> + long long int tcm_parent;
> + struct nlattr *nla;
> + int ret;
> + struct {
> + struct nlmsghdr nh;
> + struct tcmsg t;
> + char buf[256];
> + } req;
> +
> + if (!hook || !opts || !OPTS_VALID(hook, bpf_tc_opts) ||
> + !OPTS_VALID(opts, bpf_tc_opts))
> + return -EINVAL;
> + if (OPTS_GET(hook, ifindex, 0) <= 0 || !OPTS_GET(opts, prog_fd, 0) ||
> + OPTS_GET(opts, prog_id, 0))
> + return -EINVAL;
> + if (OPTS_GET(opts, priority, 0) > UINT16_MAX)
> + return -EINVAL;
> + if (flags & ~BPF_TC_F_REPLACE)
> + return -EINVAL;
> +
> + protocol = ETH_P_ALL;
> + flags = flags & BPF_TC_F_REPLACE ? NLM_F_REPLACE : NLM_F_EXCL;

()

> +
> + memset(&req, 0, sizeof(req));
> + req.nh.nlmsg_len = NLMSG_LENGTH(sizeof(struct tcmsg));
> + req.nh.nlmsg_flags =
> + NLM_F_REQUEST | NLM_F_ACK | NLM_F_CREATE | NLM_F_ECHO | flags;
> + req.nh.nlmsg_type = RTM_NEWTFILTER;
> + req.t.tcm_family = AF_UNSPEC;
> + req.t.tcm_handle = OPTS_GET(opts, handle, 0);
> + req.t.tcm_ifindex = OPTS_GET(hook, ifindex, 0);

you are OPTS_GET()ing same stuff multiple times, it might look cleaner
to use local variables for that. It will be faster also, but that's
not important here.

> + req.t.tcm_info = TC_H_MAKE(OPTS_GET(opts, priority, 0) << 16, htons(protocol));
> +
> + tcm_parent = tc_get_tcm_parent(OPTS_GET(hook, attach_point, 0), OPTS_GET(hook, parent, 0));

and this will be much shorter, positively, please use local variables
for all those input fields you care about

> + if (tcm_parent < 0)
> + return tcm_parent;
> + req.t.tcm_parent = tcm_parent;
> +
> + ret = nlattr_add(&req.nh, sizeof(req), TCA_KIND, "bpf", sizeof("bpf"));
> + if (ret < 0)
> + return ret;
> +
> + nla = nlattr_begin_nested(&req.nh, sizeof(req), TCA_OPTIONS);
> + if (!nla)
> + return -EMSGSIZE;
> +
> + ret = tc_cls_add_fd_and_name(&req.nh, sizeof(req), OPTS_GET(opts, prog_fd, 0));
> + if (ret < 0)
> + return ret;
> +
> + /* direct action mode is always enabled */
> + bpf_flags = TCA_BPF_FLAG_ACT_DIRECT;
> + ret = nlattr_add(&req.nh, sizeof(req), TCA_BPF_FLAGS,
> + &bpf_flags, sizeof(bpf_flags));
> + if (ret < 0)
> + return ret;
> +
> + nlattr_end_nested(&req.nh, nla);
> +
> + info.opts = opts;
> +
> + ret = libbpf_nl_send_recv(&req.nh, &cls_get_info, NULL, &info);
> + if (ret < 0)
> + return ret;
> +
> + /* Failed to process unicast response */
> + if (!info.processed)
> + ret = -ENOENT;

just return directly, you just did that multiple times above, why this
one is special?

> +
> + return ret;
> +}
> +
> +static int tc_cls_detach(const struct bpf_tc_hook *hook,
> + const struct bpf_tc_opts *opts, bool flush)
> +{
> + long long int tcm_parent;
> + __u32 protocol = 0;
> + int ret, c;
> + struct {
> + struct nlmsghdr nh;
> + struct tcmsg t;
> + char buf[256];
> + } req;
> +
> + if (!hook || !OPTS_VALID(hook, bpf_tc_opts) ||
> + !OPTS_VALID(opts, bpf_tc_opts))
> + return -EINVAL;
> + if (OPTS_GET(hook, ifindex, 0) <= 0 || OPTS_GET(opts, prog_fd, 0) ||
> + OPTS_GET(opts, prog_id, 0))
> + return -EINVAL;
> + c = !!OPTS_GET(opts, handle, 0) + !!OPTS_GET(opts, priority, 0);
> + if ((flush && c != 0) || (!flush && c != 2))
> + return -EINVAL;

arithmetics here looks pretty ugly, would it be too bad with logical checks?

> + if (OPTS_GET(opts, priority, 0) > UINT16_MAX)
> + return -EINVAL;
> +
> + if (!flush)
> + protocol = ETH_P_ALL;
> +
> + memset(&req, 0, sizeof(req));
> + req.nh.nlmsg_len = NLMSG_LENGTH(sizeof(struct tcmsg));
> + req.nh.nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK;
> + req.nh.nlmsg_type = RTM_DELTFILTER;
> + req.t.tcm_family = AF_UNSPEC;
> + if (!flush)
> + req.t.tcm_handle = OPTS_GET(opts, handle, 0);
> + req.t.tcm_ifindex = OPTS_GET(hook, ifindex, 0);
> + if (!flush)
> + req.t.tcm_info = TC_H_MAKE(OPTS_GET(opts, priority, 0) << 16,

OPTS_GET()s just make everything uglier and unnecessarily verbose

> + htons(protocol));
> +
> + tcm_parent = tc_get_tcm_parent(OPTS_GET(hook, attach_point, 0), OPTS_GET(hook, parent, 0));
> + if (tcm_parent < 0)
> + return tcm_parent;
> + req.t.tcm_parent = tcm_parent;
> +
> + if (!flush) {
> + ret = nlattr_add(&req.nh, sizeof(req), TCA_KIND, "bpf", sizeof("bpf"));
> + if (ret < 0)
> + return ret;
> + }
> +
> + return libbpf_nl_send_recv(&req.nh, NULL, NULL, NULL);
> +}
> +

[...]

> + tcm_parent = tc_get_tcm_parent(OPTS_GET(hook, attach_point, 0), OPTS_GET(hook, parent, 0));
> + if (tcm_parent < 0)
> + return tcm_parent;
> + req.t.tcm_parent = tcm_parent;
> +
> + ret = nlattr_add(&req.nh, sizeof(req), TCA_KIND, "bpf", sizeof("bpf"));
> + if (ret < 0)
> + return ret;
> +
> + if (OPTS_GET(opts, prog_fd, 0)) {
> + struct bpf_prog_info info = {};
> + ret = bpf_obj_get_info_by_fd(OPTS_GET(opts, prog_fd, 0), &info, &(__u32){sizeof(info)});

same as before, use dedicated variable

> + if (ret < 0)
> + return ret;
> +
> + pinfo.match_prog_id = info.id;
> + } else
> + pinfo.match_prog_id = OPTS_GET(opts, prog_id, 0);

when one branch of if has {}, the other one has to have it as well, please fix

> +
> + pinfo.opts = opts;
> +
> + ret = libbpf_nl_send_recv(&req.nh, cls_get_info, NULL, &pinfo);
> + if (ret < 0)
> + return ret;
> +
> + if (!pinfo.processed)
> + ret = -ENOENT;

direct return

> +
> + return ret;
> +}
> --
> 2.30.2
>