loop: remove cgo dependency

it was used only for some const definitions, just copy their value.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

pkg/loopback/attach_loopback.go

@@ -1,4 +1,4 @@
-//go:build linux && cgo
+//go:build linux
 
 package loopback
 

pkg/loopback/attach_test.go

@@ -1,4 +1,4 @@
-//go:build linux && cgo
+//go:build linux
 
 package loopback
 

pkg/loopback/ioctl.go

@@ -1,4 +1,4 @@
-//go:build linux && cgo
+//go:build linux
 
 package loopback
 

pkg/loopback/loop_wrapper.go

@@ -1,21 +1,7 @@
-//go:build linux && cgo
+//go:build linux
 
 package loopback
 
-/*
-#include <linux/loop.h> // FIXME: present only for defines, maybe we can remove it?
-
-#ifndef LOOP_CTL_GET_FREE
-  #define LOOP_CTL_GET_FREE 0x4C82
-#endif
-
-#ifndef LO_FLAGS_PARTSCAN
-  #define LO_FLAGS_PARTSCAN 8
-#endif
-
-*/
-import "C"
-
 type loopInfo64 struct {
 	loDevice         uint64 /* ioctl r/o */
 	loInode          uint64 /* ioctl r/o */
@@ -34,19 +20,19 @@ type loopInfo64 struct {
 
 // IOCTL consts
 const (
-	LoopSetFd       = C.LOOP_SET_FD
-	LoopCtlGetFree  = C.LOOP_CTL_GET_FREE
-	LoopGetStatus64 = C.LOOP_GET_STATUS64
-	LoopSetStatus64 = C.LOOP_SET_STATUS64
-	LoopClrFd       = C.LOOP_CLR_FD
-	LoopSetCapacity = C.LOOP_SET_CAPACITY
+	LoopSetFd       = 0x4C00
+	LoopCtlGetFree  = 0x4C82
+	LoopGetStatus64 = 0x4C05
+	LoopSetStatus64 = 0x4C04
+	LoopClrFd       = 0x4C01
+	LoopSetCapacity = 0x4C07
 )
 
 // LOOP consts.
 const (
-	LoFlagsAutoClear = C.LO_FLAGS_AUTOCLEAR
-	LoFlagsReadOnly  = C.LO_FLAGS_READ_ONLY
-	LoFlagsPartScan  = C.LO_FLAGS_PARTSCAN
-	LoKeySize        = C.LO_KEY_SIZE
-	LoNameSize       = C.LO_NAME_SIZE
+	LoFlagsAutoClear = 0x4C07
+	LoFlagsReadOnly  = 1
+	LoFlagsPartScan  = 8
+	LoKeySize        = 32
+	LoNameSize       = 64
 )

pkg/loopback/loopback.go

@@ -1,4 +1,4 @@
-//go:build linux && cgo
+//go:build linux
 
 package loopback