path: Use loops in new kernels

In "large" kernels we have support for loops. So use them in prepend_path (a function used in path resolution) to improve loading time. Signed-off-by: Anastasios Papagiannis <[email protected]>
cilium · Jan 16, 2024 · 57f7b8d · 57f7b8d
1 parent 95974f4
commit 57f7b8d
Show file tree

Hide file tree

Showing 2 changed files with 20 additions and 4 deletions.
diff --git a/bpf/lib/bpf_task.h b/bpf/lib/bpf_task.h
@@ -17,6 +17,7 @@
 
 #ifdef __LARGE_BPF_PROG
 #define PROBE_CWD_READ_ITERATIONS 128
+#define PROBE_CWD_READ_UNROLL	  4
 #else
 #define PROBE_CWD_READ_ITERATIONS 11
 #endif

diff --git a/bpf/process/bpf_process_event.h b/bpf/process/bpf_process_event.h
@@ -263,15 +263,30 @@ prepend_path(const struct path *path, const struct path *root, char *bf,
 	probe_read(&data.vfsmnt, sizeof(data.vfsmnt), _(&path->mnt));
 	data.mnt = real_mount(data.vfsmnt);
 
-#ifndef __V61_BPF_PROG
+#if defined(__V61_BPF_PROG)
+	loop(PROBE_CWD_READ_ITERATIONS, cwd_read_v61, (void *)&data, 0);
+#elif defined(__LARGE_BPF_PROG)
+	// In large kernels we have support for loops so there is no
+	// neet to unroll here. If we just remove the unroll we get
+	// verification error (too large program). To overcome this,
+	// we do "some" loop unrolling.
+	for (int i = 0; i < PROBE_CWD_READ_ITERATIONS / PROBE_CWD_READ_UNROLL; ++i) {
+		if (cwd_read(&data))
+			break;
+		if (cwd_read(&data))
+			break;
+		if (cwd_read(&data))
+			break;
+		if (cwd_read(&data))
+			break;
+	}
+#else
 #pragma unroll
 	for (int i = 0; i < PROBE_CWD_READ_ITERATIONS; ++i) {
 		if (cwd_read(&data))
 			break;
 	}
-#else
-	loop(PROBE_CWD_READ_ITERATIONS, cwd_read_v61, (void *)&data, 0);
-#endif /* __V61_BPF_PROG */
+#endif
 
 	if (data.bptr == *buffer) {
 		*buflen = 0;