bpf: Convert bpf_preload.ko to use light skeleton.

The main change is a move of the single line
  #include "iterators.lskel.h"
from iterators/iterators.c to bpf_preload_kern.c.
Which means that generated light skeleton can be used from user space or
user mode driver like iterators.c or from the kernel module or the kernel itself.
The direct use of light skeleton from the kernel module simplifies the code,
since UMD is no longer necessary. The libbpf.a required user space and UMD. The
CO-RE in the kernel and generated "loader bpf program" used by the light
skeleton are capable to perform complex loading operations traditionally
provided by libbpf. In addition UMD approach was launching UMD process
every time bpffs has to be mounted. With light skeleton in the kernel
the bpf_preload kernel module loads bpf iterators once and pins them
multiple times into different bpffs mounts.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220209232001.27490-6-alexei.starovoitov@gmail.com

1 files changed, 10 insertions, 29 deletions

diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
index 5a8d9f7467bf..4f841e16779e 100644
--- a/kernel/bpf/inode.c
+++ b/kernel/bpf/inode.c
@@ -710,11 +710,10 @@ static DEFINE_MUTEX(bpf_preload_lock);
 static int populate_bpffs(struct dentry *parent)
 {
 	struct bpf_preload_info objs[BPF_PRELOAD_LINKS] = {};
-	struct bpf_link *links[BPF_PRELOAD_LINKS] = {};
 	int err = 0, i;
 
 	/* grab the mutex to make sure the kernel interactions with bpf_preload
-	 * UMD are serialized
+	 * are serialized
 	 */
 	mutex_lock(&bpf_preload_lock);
 
@@ -722,40 +721,22 @@ static int populate_bpffs(struct dentry *parent)
 	if (!bpf_preload_mod_get())
 		goto out;
 
-	if (!bpf_preload_ops->info.tgid) {
-		/* preload() will start UMD that will load BPF iterator programs */
-		err = bpf_preload_ops->preload(objs);
-		if (err)
+	err = bpf_preload_ops->preload(objs);
+	if (err)
+		goto out_put;
+	for (i = 0; i < BPF_PRELOAD_LINKS; i++) {
+		bpf_link_inc(objs[i].link);
+		err = bpf_iter_link_pin_kernel(parent,
+					       objs[i].link_name, objs[i].link);
+		if (err) {
+			bpf_link_put(objs[i].link);
 			goto out_put;
-		for (i = 0; i < BPF_PRELOAD_LINKS; i++) {
-			links[i] = bpf_link_by_id(objs[i].link_id);
-			if (IS_ERR(links[i])) {
-				err = PTR_ERR(links[i]);
-				goto out_put;
-			}
 		}
-		for (i = 0; i < BPF_PRELOAD_LINKS; i++) {
-			err = bpf_iter_link_pin_kernel(parent,
-						       objs[i].link_name, links[i]);
-			if (err)
-				goto out_put;
-			/* do not unlink successfully pinned links even
-			 * if later link fails to pin
-			 */
-			links[i] = NULL;
-		}
-		/* finish() will tell UMD process to exit */
-		err = bpf_preload_ops->finish();
-		if (err)
-			goto out_put;
 	}
 out_put:
 	bpf_preload_mod_put();
 out:
 	mutex_unlock(&bpf_preload_lock);
-	for (i = 0; i < BPF_PRELOAD_LINKS && err; i++)
-		if (!IS_ERR_OR_NULL(links[i]))
-			bpf_link_put(links[i]);
 	return err;
 }