libbpf: Streamline error reporting for high-level APIs

Implement changes to error reporting for high-level libbpf APIs to make them
less surprising and less error-prone to users:
  - in all the cases when error happens, errno is set to an appropriate error
    value;
  - in libbpf 1.0 mode, all pointer-returning APIs return NULL on error and
    error code is communicated through errno; this applies both to APIs that
    already returned NULL before (so now they communicate more detailed error
    codes), as well as for many APIs that used ERR_PTR() macro and encoded
    error numbers as fake pointers.
  - in legacy (default) mode, those APIs that were returning ERR_PTR(err),
    continue doing so, but still set errno.

With these changes, errno can be always used to extract actual error,
regardless of legacy or libbpf 1.0 modes. This is utilized internally in
libbpf in places where libbpf uses it's own high-level APIs.
libbpf_get_error() is adapted to handle both cases completely transparently to
end-users (and is used by libbpf consistently as well).

More context, justification, and discussion can be found in "Libbpf: the road
to v1.0" document ([0]).

  [0] https://docs.google.com/document/d/1UyjTZuPFWiPFyKk1tV5an11_iaRuec6U-ZESZ54nNTY

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20210525035935.1461796-5-andrii@kernel.org

1 files changed, 47 insertions, 34 deletions

diff --git a/tools/lib/bpf/netlink.c b/tools/lib/bpf/netlink.c
index 47444588e0d2..d743c8721aa7 100644
--- a/tools/lib/bpf/netlink.c
+++ b/tools/lib/bpf/netlink.c
@@ -225,22 +225,26 @@ static int __bpf_set_link_xdp_fd_replace(int ifindex, int fd, int old_fd,
 int bpf_set_link_xdp_fd_opts(int ifindex, int fd, __u32 flags,
 			     const struct bpf_xdp_set_link_opts *opts)
 {
-	int old_fd = -1;
+	int old_fd = -1, ret;
 
 	if (!OPTS_VALID(opts, bpf_xdp_set_link_opts))
-		return -EINVAL;
+		return libbpf_err(-EINVAL);
 
 	if (OPTS_HAS(opts, old_fd)) {
 		old_fd = OPTS_GET(opts, old_fd, -1);
 		flags |= XDP_FLAGS_REPLACE;
 	}
 
-	return __bpf_set_link_xdp_fd_replace(ifindex, fd, old_fd, flags);
+	ret = __bpf_set_link_xdp_fd_replace(ifindex, fd, old_fd, flags);
+	return libbpf_err(ret);
 }
 
 int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
 {
-	return __bpf_set_link_xdp_fd_replace(ifindex, fd, 0, flags);
+	int ret;
+
+	ret = __bpf_set_link_xdp_fd_replace(ifindex, fd, 0, flags);
+	return libbpf_err(ret);
 }
 
 static int __dump_link_nlmsg(struct nlmsghdr *nlh,
@@ -321,13 +325,13 @@ int bpf_get_link_xdp_info(int ifindex, struct xdp_link_info *info,
 	};
 
 	if (flags & ~XDP_FLAGS_MASK || !info_size)
-		return -EINVAL;
+		return libbpf_err(-EINVAL);
 
 	/* Check whether the single {HW,DRV,SKB} mode is set */
 	flags &= (XDP_FLAGS_SKB_MODE | XDP_FLAGS_DRV_MODE | XDP_FLAGS_HW_MODE);
 	mask = flags - 1;
 	if (flags && flags & mask)
-		return -EINVAL;
+		return libbpf_err(-EINVAL);
 
 	xdp_id.ifindex = ifindex;
 	xdp_id.flags = flags;
@@ -341,7 +345,7 @@ int bpf_get_link_xdp_info(int ifindex, struct xdp_link_info *info,
 		memset((void *) info + sz, 0, info_size - sz);
 	}
 
-	return ret;
+	return libbpf_err(ret);
 }
 
 static __u32 get_xdp_id(struct xdp_link_info *info, __u32 flags)
@@ -369,7 +373,7 @@ int bpf_get_link_xdp_id(int ifindex, __u32 *prog_id, __u32 flags)
 	if (!ret)
 		*prog_id = get_xdp_id(&info, flags);
 
-	return ret;
+	return libbpf_err(ret);
 }
 
 typedef int (*qdisc_config_t)(struct nlmsghdr *nh, struct tcmsg *t,
@@ -463,11 +467,14 @@ static int tc_qdisc_delete(struct bpf_tc_hook *hook)
 
 int bpf_tc_hook_create(struct bpf_tc_hook *hook)
 {
+	int ret;
+
 	if (!hook || !OPTS_VALID(hook, bpf_tc_hook) ||
 	    OPTS_GET(hook, ifindex, 0) <= 0)
-		return -EINVAL;
+		return libbpf_err(-EINVAL);
 
-	return tc_qdisc_create_excl(hook);
+	ret = tc_qdisc_create_excl(hook);
+	return libbpf_err(ret);
 }
 
 static int __bpf_tc_detach(const struct bpf_tc_hook *hook,
@@ -478,18 +485,18 @@ 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;
+		return libbpf_err(-EINVAL);
 
 	switch (OPTS_GET(hook, attach_point, 0)) {
 	case BPF_TC_INGRESS:
 	case BPF_TC_EGRESS:
-		return __bpf_tc_detach(hook, NULL, true);
+		return libbpf_err(__bpf_tc_detach(hook, NULL, true));
 	case BPF_TC_INGRESS | BPF_TC_EGRESS:
-		return tc_qdisc_delete(hook);
+		return libbpf_err(tc_qdisc_delete(hook));
 	case BPF_TC_CUSTOM:
-		return -EOPNOTSUPP;
+		return libbpf_err(-EOPNOTSUPP);
 	default:
-		return -EINVAL;
+		return libbpf_err(-EINVAL);
 	}
 }
 
@@ -574,7 +581,7 @@ int bpf_tc_attach(const struct bpf_tc_hook *hook, struct bpf_tc_opts *opts)
 	if (!hook || !opts ||
 	    !OPTS_VALID(hook, bpf_tc_hook) ||
 	    !OPTS_VALID(opts, bpf_tc_opts))
-		return -EINVAL;
+		return libbpf_err(-EINVAL);
 
 	ifindex      = OPTS_GET(hook, ifindex, 0);
 	parent       = OPTS_GET(hook, parent, 0);
@@ -587,11 +594,11 @@ int bpf_tc_attach(const struct bpf_tc_hook *hook, struct bpf_tc_opts *opts)
 	flags        = OPTS_GET(opts, flags, 0);
 
 	if (ifindex <= 0 || !prog_fd || prog_id)
-		return -EINVAL;
+		return libbpf_err(-EINVAL);
 	if (priority > UINT16_MAX)
-		return -EINVAL;
+		return libbpf_err(-EINVAL);
 	if (flags & ~BPF_TC_F_REPLACE)
-		return -EINVAL;
+		return libbpf_err(-EINVAL);
 
 	flags = (flags & BPF_TC_F_REPLACE) ? NLM_F_REPLACE : NLM_F_EXCL;
 	protocol = ETH_P_ALL;
@@ -608,32 +615,32 @@ int bpf_tc_attach(const struct bpf_tc_hook *hook, struct bpf_tc_opts *opts)
 
 	ret = tc_get_tcm_parent(attach_point, &parent);
 	if (ret < 0)
-		return ret;
+		return libbpf_err(ret);
 	req.tc.tcm_parent = parent;
 
 	ret = nlattr_add(&req.nh, sizeof(req), TCA_KIND, "bpf", sizeof("bpf"));
 	if (ret < 0)
-		return ret;
+		return libbpf_err(ret);
 	nla = nlattr_begin_nested(&req.nh, sizeof(req), TCA_OPTIONS);
 	if (!nla)
-		return -EMSGSIZE;
+		return libbpf_err(-EMSGSIZE);
 	ret = tc_add_fd_and_name(&req.nh, sizeof(req), prog_fd);
 	if (ret < 0)
-		return ret;
+		return libbpf_err(ret);
 	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;
+		return libbpf_err(ret);
 	nlattr_end_nested(&req.nh, nla);
 
 	info.opts = opts;
 
 	ret = libbpf_netlink_send_recv(&req.nh, get_tc_info, NULL, &info);
 	if (ret < 0)
-		return ret;
+		return libbpf_err(ret);
 	if (!info.processed)
-		return -ENOENT;
+		return libbpf_err(-ENOENT);
 	return ret;
 }
 
@@ -708,7 +715,13 @@ static int __bpf_tc_detach(const struct bpf_tc_hook *hook,
 int bpf_tc_detach(const struct bpf_tc_hook *hook,
 		  const struct bpf_tc_opts *opts)
 {
-	return !opts ? -EINVAL : __bpf_tc_detach(hook, opts, false);
+	int ret;
+
+	if (!opts)
+		return libbpf_err(-EINVAL);
+
+	ret = __bpf_tc_detach(hook, opts, false);
+	return libbpf_err(ret);
 }
 
 int bpf_tc_query(const struct bpf_tc_hook *hook, struct bpf_tc_opts *opts)
@@ -725,7 +738,7 @@ int bpf_tc_query(const struct bpf_tc_hook *hook, struct bpf_tc_opts *opts)
 	if (!hook || !opts ||
 	    !OPTS_VALID(hook, bpf_tc_hook) ||
 	    !OPTS_VALID(opts, bpf_tc_opts))
-		return -EINVAL;
+		return libbpf_err(-EINVAL);
 
 	ifindex      = OPTS_GET(hook, ifindex, 0);
 	parent       = OPTS_GET(hook, parent, 0);
@@ -739,9 +752,9 @@ int bpf_tc_query(const struct bpf_tc_hook *hook, struct bpf_tc_opts *opts)
 
 	if (ifindex <= 0 || flags || prog_fd || prog_id ||
 	    !handle || !priority)
-		return -EINVAL;
+		return libbpf_err(-EINVAL);
 	if (priority > UINT16_MAX)
-		return -EINVAL;
+		return libbpf_err(-EINVAL);
 
 	protocol = ETH_P_ALL;
 
@@ -756,19 +769,19 @@ int bpf_tc_query(const struct bpf_tc_hook *hook, struct bpf_tc_opts *opts)
 
 	ret = tc_get_tcm_parent(attach_point, &parent);
 	if (ret < 0)
-		return ret;
+		return libbpf_err(ret);
 	req.tc.tcm_parent = parent;
 
 	ret = nlattr_add(&req.nh, sizeof(req), TCA_KIND, "bpf", sizeof("bpf"));
 	if (ret < 0)
-		return ret;
+		return libbpf_err(ret);
 
 	info.opts = opts;
 
 	ret = libbpf_netlink_send_recv(&req.nh, get_tc_info, NULL, &info);
 	if (ret < 0)
-		return ret;
+		return libbpf_err(ret);
 	if (!info.processed)
-		return -ENOENT;
+		return libbpf_err(-ENOENT);
 	return ret;
 }