fix: add runtime.KeepAlive to keep alive descriptors

Without them, when we pass the result of Fd() into unix.Syscall, Go runtime is free to call finalizer set in os.newFile.
More info [here](golang/go#34810).

The proper fix is to either:

1. Use unix.Open/unix.Close as descriptors (ints) everywhere in the Device code. This should hide fd's from Go runtime.
2. Use os.File.SyscallConn().Control which guarantees that descriptor survives. This will also do not put fd's into the blocking mode.

Otherwise, even with os.File.Close it's not guaranteed that runtime.SetFinalizer will not come for `os.File.file`.

Signed-off-by: Dmitriy Matrenichev <[email protected]>

block/device_linux.go

@@ -10,6 +10,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"runtime"
 	"strconv"
 	"strings"
 	"unsafe"
@@ -45,6 +46,8 @@ func (d *Device) GetSize() (uint64, error) {
 		return 0, errno
 	}
 
+	runtime.KeepAlive(d)
+
 	return devsize, nil
 }
 
@@ -61,6 +64,8 @@ func (d *Device) GetIOSize() (uint, error) {
 		}
 	}
 
+	runtime.KeepAlive(d)
+
 	return DefaultBlockSize, nil
 }
 
@@ -72,6 +77,8 @@ func (d *Device) GetSectorSize() uint {
 		return DefaultBlockSize
 	}
 
+	runtime.KeepAlive(d)
+
 	return size
 }
 
@@ -83,6 +90,8 @@ func (d *Device) IsCD() bool {
 		return false
 	}
 
+	runtime.KeepAlive(d)
+
 	return true
 }
 
@@ -92,6 +101,8 @@ func (d *Device) IsCDNoMedia() bool {
 
 	arg, _, errno := unix.Syscall(unix.SYS_IOCTL, d.f.Fd(), uintptr(CDROM_DRIVE_STATUS), 0)
 
+	runtime.KeepAlive(d)
+
 	return errno == 0 && (arg == 1 || arg == 2)
 }
 
@@ -106,6 +117,8 @@ func (d *Device) GetDevNo() (uint64, error) {
 		return 0, err
 	}
 
+	runtime.KeepAlive(d)
+
 	d.devNo = st.Rdev
 
 	return d.devNo, nil
@@ -143,6 +156,8 @@ func (d *Device) IsReadOnly() (bool, error) {
 		return false, errno
 	}
 
+	runtime.KeepAlive(d)
+
 	return flags != 0, nil
 }
 
@@ -279,6 +294,8 @@ func (d *Device) lock(exclusive bool, flag int) error {
 		if err := unix.Flock(int(d.f.Fd()), flag); !errors.Is(err, unix.EINTR) {
 			return err
 		}
+
+		runtime.KeepAlive(d)
 	}
 }