Per CPU map needed API and selftest (#156)

* Add API 'GetValueReadInto' which lets you specify the byte
slice for the map lookup to read into

Signed-off-by: grantseltzer <grantseltzer@gmail.com>

libbpfgo.go

@@ -670,6 +670,14 @@ func (b *BPFMap) ValueSize() int {
 	return int(C.bpf_map__value_size(b.bpfMap))
 }
 
+func (b *BPFMap) SetValueSize(size uint32) error {
+	errC := C.bpf_map__set_value_size(b.bpfMap, C.uint(size))
+	if errC != 0 {
+		return fmt.Errorf("could not set map value size: %w", syscall.Errno(-errC))
+	}
+	return nil
+}
+
 // GetValue takes a pointer to the key which is stored in the map.
 // It returns the associated value as a slice of bytes.
 // All basic types, and structs are supported as keys.
@@ -700,6 +708,21 @@ func (b *BPFMap) GetValueFlags(key unsafe.Pointer, flags MapFlag) ([]byte, error
 	return value, nil
 }
 
+// GetValueReadInto is like GetValue, except it allows the caller to pass in
+// a pointer to the slice of bytes that the value would be read into from the
+// map.
+// This is useful for reading from maps with variable sizes, especially
+// per-cpu arrays and hash maps where the size of each value depends on the
+// number of CPUs
+func (b *BPFMap) GetValueReadInto(key unsafe.Pointer, value *[]byte) error {
+	valuePtr := unsafe.Pointer(&(*value)[0])
+	errC := C.bpf_map__lookup_elem(b.bpfMap, key, C.ulong(b.KeySize()), valuePtr, C.ulong(len(*value)), 0)
+	if errC != 0 {
+		return fmt.Errorf("failed to lookup value %v in map %s: %w", key, b.name, syscall.Errno(-errC))
+	}
+	return nil
+}
+
 // BPFMapBatchOpts mirrors the C structure bpf_map_batch_opts.
 type BPFMapBatchOpts struct {
 	Sz        uint64

selftest/percpu/Makefile

@@ -0,0 +1 @@
+../common/Makefile

selftest/percpu/README.md

@@ -0,0 +1 @@
+# PER CPU

selftest/percpu/go.mod

@@ -0,0 +1,7 @@
+module github.com/aquasecurity/libbpfgo/selftest/perfbuffers
+
+go 1.16
+
+require github.com/aquasecurity/libbpfgo v0.2.1-libbpf-0.4.0
+
+replace github.com/aquasecurity/libbpfgo => ../../

selftest/percpu/go.sum

@@ -0,0 +1,11 @@
+github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+golang.org/x/sys v0.0.0-20210514084401-e8d321eab015/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

selftest/percpu/main.bpf.c

@@ -0,0 +1,33 @@
+//+build ignore
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>  
+
+#ifdef asm_inline
+#undef asm_inline
+#define asm_inline asm
+#endif
+
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, __u32);
+	__type(value, __u64);
+} percpu_hash SEC(".maps");
+
+SEC("fentry/__x64_sys_mmap")
+int mmap_fentry(struct pt_regs *ctx)
+{
+    __u32 key = 0;
+    __u8 *value = bpf_map_lookup_elem(&percpu_hash, &key);
+    if (value) {
+        *value += 1;
+        bpf_printk("%d",*value);
+        return 0;
+    }
+
+    bpf_printk("nothing");
+
+    return 0;
+}
+char LICENSE[] SEC("license") = "GPL";

selftest/percpu/main.go

@@ -0,0 +1,74 @@
+package main
+
+import "C"
+
+import (
+	"encoding/binary"
+	"fmt"
+	"os"
+	"runtime"
+	"syscall"
+	"time"
+	"unsafe"
+
+	bpf "github.com/aquasecurity/libbpfgo"
+)
+
+func main() {
+
+	bpfModule, err := bpf.NewModuleFromFile("main.bpf.o")
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(-1)
+	}
+	defer bpfModule.Close()
+
+	err = bpfModule.BPFLoadObject()
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(-1)
+	}
+
+	prog, err := bpfModule.GetProgram("mmap_fentry")
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(-1)
+	}
+
+	link, err := prog.AttachGeneric()
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(-1)
+	}
+	if link.GetFd() == 0 {
+		os.Exit(-1)
+	}
+
+	go func() {
+		for {
+			syscall.Mmap(999, 999, 999, 1, 1)
+			time.Sleep(time.Millisecond * 30)
+		}
+	}()
+
+	lostEventCounterMap, err := bpfModule.GetMap("percpu_hash")
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(-1)
+	}
+
+	time.Sleep(time.Second * 2)
+	key := 0
+	values := make([]byte, 8*runtime.NumCPU())
+	err = lostEventCounterMap.GetValueReadInto(unsafe.Pointer(&key), &values)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(-1)
+	}
+
+	last := 0
+	for i := 0; i < runtime.NumCPU(); i++ {
+		fmt.Printf("CPU %d: %d\n", i, binary.LittleEndian.Uint32(values[last:last+8]))
+		last += 8
+	}
+}

selftest/percpu/run.sh

@@ -0,0 +1 @@
+../common/run-5.8.sh