Merge release-20210927.0-71-g4e2cc2bef (automated)

1 files changed, 33 insertions, 0 deletions

diff --git a/pkg/tcpip/link/sharedmem/sharedmem_unsafe.go b/pkg/tcpip/link/sharedmem/sharedmem_unsafe.go
index f7e816a41..d974c266e 100644
--- a/pkg/tcpip/link/sharedmem/sharedmem_unsafe.go
+++ b/pkg/tcpip/link/sharedmem/sharedmem_unsafe.go
@@ -15,7 +15,12 @@
 package sharedmem
 
 import (
+	"fmt"
+	"reflect"
 	"unsafe"
+
+	"golang.org/x/sys/unix"
+	"gvisor.dev/gvisor/pkg/memutil"
 )
 
 // sharedDataPointer converts the shared data slice into a pointer so that it
@@ -23,3 +28,31 @@ import (
 func sharedDataPointer(sharedData []byte) *uint32 {
 	return (*uint32)(unsafe.Pointer(&sharedData[0:4][0]))
 }
+
+// getBuffer returns a memory region mapped to the full contents of the given
+// file descriptor.
+func getBuffer(fd int) ([]byte, error) {
+	var s unix.Stat_t
+	if err := unix.Fstat(fd, &s); err != nil {
+		return nil, err
+	}
+
+	// Check that size doesn't overflow an int.
+	if s.Size > int64(^uint(0)>>1) {
+		return nil, unix.EDOM
+	}
+
+	addr, err := memutil.MapFile(0 /* addr */, uintptr(s.Size), unix.PROT_READ|unix.PROT_WRITE, unix.MAP_SHARED|unix.MAP_FILE, uintptr(fd), 0 /*offset*/)
+	if err != nil {
+		return nil, fmt.Errorf("failed to map memory for buffer fd: %d, error: %s", fd, err)
+	}
+
+	// Use unsafe to conver addr into a []byte.
+	var b []byte
+	hdr := (*reflect.SliceHeader)(unsafe.Pointer(&b))
+	hdr.Data = addr
+	hdr.Len = int(s.Size)
+	hdr.Cap = int(s.Size)
+
+	return b, nil
+}