selftest/bpf: Make bpf_iter selftest compilable against old vmlinux.h

It's good to be able to compile bpf_iter selftest even on systems that don't
have the very latest vmlinux.h, e.g., for libbpf tests against older kernels in
Travis CI. To that extent, re-define bpf_iter_meta and corresponding bpf_iter
context structs in each selftest. To avoid type clashes with vmlinux.h, rename
vmlinux.h's definitions to get them out of the way.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Link: https://lore.kernel.org/bpf/20200518234516.3915052-1-andriin@fb.com

tools/testing/selftests/bpf/progs/bpf_iter_bpf_map.c

@@ -1,11 +1,27 @@
 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (c) 2020 Facebook */
+/* "undefine" structs in vmlinux.h, because we "override" them below */
+#define bpf_iter_meta bpf_iter_meta___not_used
+#define bpf_iter__bpf_map bpf_iter__bpf_map___not_used
 #include "vmlinux.h"
+#undef bpf_iter_meta
+#undef bpf_iter__bpf_map
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 
 char _license[] SEC("license") = "GPL";
 
+struct bpf_iter_meta {
+	struct seq_file *seq;
+	__u64 session_id;
+	__u64 seq_num;
+} __attribute__((preserve_access_index));
+
+struct bpf_iter__bpf_map {
+	struct bpf_iter_meta *meta;
+	struct bpf_map *map;
+} __attribute__((preserve_access_index));
+
 SEC("iter/bpf_map")
 int dump_bpf_map(struct bpf_iter__bpf_map *ctx)
 {

tools/testing/selftests/bpf/progs/bpf_iter_ipv6_route.c

@@ -1,9 +1,25 @@
 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (c) 2020 Facebook */
+/* "undefine" structs in vmlinux.h, because we "override" them below */
+#define bpf_iter_meta bpf_iter_meta___not_used
+#define bpf_iter__ipv6_route bpf_iter__ipv6_route___not_used
 #include "vmlinux.h"
+#undef bpf_iter_meta
+#undef bpf_iter__ipv6_route
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 
+struct bpf_iter_meta {
+	struct seq_file *seq;
+	__u64 session_id;
+	__u64 seq_num;
+} __attribute__((preserve_access_index));
+
+struct bpf_iter__ipv6_route {
+	struct bpf_iter_meta *meta;
+	struct fib6_info *rt;
+} __attribute__((preserve_access_index));
+
 char _license[] SEC("license") = "GPL";
 
 extern bool CONFIG_IPV6_SUBTREES __kconfig __weak;

tools/testing/selftests/bpf/progs/bpf_iter_netlink.c

@@ -1,6 +1,11 @@
 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (c) 2020 Facebook */
+/* "undefine" structs in vmlinux.h, because we "override" them below */
+#define bpf_iter_meta bpf_iter_meta___not_used
+#define bpf_iter__netlink bpf_iter__netlink___not_used
 #include "vmlinux.h"
+#undef bpf_iter_meta
+#undef bpf_iter__netlink
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 
@@ -9,6 +14,17 @@ char _license[] SEC("license") = "GPL";
 #define sk_rmem_alloc	sk_backlog.rmem_alloc
 #define sk_refcnt	__sk_common.skc_refcnt
 
+struct bpf_iter_meta {
+	struct seq_file *seq;
+	__u64 session_id;
+	__u64 seq_num;
+} __attribute__((preserve_access_index));
+
+struct bpf_iter__netlink {
+	struct bpf_iter_meta *meta;
+	struct netlink_sock *sk;
+} __attribute__((preserve_access_index));
+
 static inline struct inode *SOCK_INODE(struct socket *socket)
 {
 	return &container_of(socket, struct socket_alloc, socket)->vfs_inode;

tools/testing/selftests/bpf/progs/bpf_iter_task.c

@@ -1,11 +1,27 @@
 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (c) 2020 Facebook */
+/* "undefine" structs in vmlinux.h, because we "override" them below */
+#define bpf_iter_meta bpf_iter_meta___not_used
+#define bpf_iter__task bpf_iter__task___not_used
 #include "vmlinux.h"
+#undef bpf_iter_meta
+#undef bpf_iter__task
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 
 char _license[] SEC("license") = "GPL";
 
+struct bpf_iter_meta {
+	struct seq_file *seq;
+	__u64 session_id;
+	__u64 seq_num;
+} __attribute__((preserve_access_index));
+
+struct bpf_iter__task {
+	struct bpf_iter_meta *meta;
+	struct task_struct *task;
+} __attribute__((preserve_access_index));
+
 SEC("iter/task")
 int dump_task(struct bpf_iter__task *ctx)
 {

tools/testing/selftests/bpf/progs/bpf_iter_task_file.c

@@ -1,11 +1,29 @@
 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (c) 2020 Facebook */
+/* "undefine" structs in vmlinux.h, because we "override" them below */
+#define bpf_iter_meta bpf_iter_meta___not_used
+#define bpf_iter__task_file bpf_iter__task_file___not_used
 #include "vmlinux.h"
+#undef bpf_iter_meta
+#undef bpf_iter__task_file
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 
 char _license[] SEC("license") = "GPL";
 
+struct bpf_iter_meta {
+	struct seq_file *seq;
+	__u64 session_id;
+	__u64 seq_num;
+} __attribute__((preserve_access_index));
+
+struct bpf_iter__task_file {
+	struct bpf_iter_meta *meta;
+	struct task_struct *task;
+	__u32 fd;
+	struct file *file;
+} __attribute__((preserve_access_index));
+
 SEC("iter/task_file")
 int dump_task_file(struct bpf_iter__task_file *ctx)
 {

tools/testing/selftests/bpf/progs/bpf_iter_test_kern_common.h

@@ -1,11 +1,27 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /* Copyright (c) 2020 Facebook */
+/* "undefine" structs in vmlinux.h, because we "override" them below */
+#define bpf_iter_meta bpf_iter_meta___not_used
+#define bpf_iter__task bpf_iter__task___not_used
 #include "vmlinux.h"
+#undef bpf_iter_meta
+#undef bpf_iter__task
 #include <bpf/bpf_helpers.h>
 
 char _license[] SEC("license") = "GPL";
 int count = 0;
 
+struct bpf_iter_meta {
+	struct seq_file *seq;
+	__u64 session_id;
+	__u64 seq_num;
+} __attribute__((preserve_access_index));
+
+struct bpf_iter__task {
+	struct bpf_iter_meta *meta;
+	struct task_struct *task;
+} __attribute__((preserve_access_index));
+
 SEC("iter/task")
 int dump_task(struct bpf_iter__task *ctx)
 {