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The raw blocking fd had three lifecycle bugs: close() does not wake a thread blocked in recvfrom, the watchdog and the error path both closed the fd without coordination, and a closed fd number could be recycled to an unrelated connection that the lingering reader would then consume from and the second close would tear down. Wrapping the nonblocking fd in os.File gives poller-based reads that Close wakes, idempotent close, and no reuse while a read is in flight.
92 lines
2.0 KiB
Go
92 lines
2.0 KiB
Go
//go:build linux
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package usbip
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import (
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"bytes"
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"os"
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"golang.org/x/sys/unix"
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)
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const ueventReceiveBufferSize = 1 << 20
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// ueventListener wraps the netlink socket in an *os.File so the fd is
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// owned by the Go runtime poller: Close wakes a goroutine blocked in
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// WaitUSBEvent, is idempotent, and the fd number cannot be recycled to
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// another connection while a read is still in flight — all of which a
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// raw fd with blocking Recvfrom gets wrong.
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type ueventListener struct {
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file *os.File
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}
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func newUEventListener() (*ueventListener, error) {
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fd, err := unix.Socket(unix.AF_NETLINK, unix.SOCK_DGRAM|unix.SOCK_NONBLOCK|unix.SOCK_CLOEXEC, unix.NETLINK_KOBJECT_UEVENT)
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if err != nil {
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return nil, err
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}
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_ = unix.SetsockoptInt(fd, unix.SOL_SOCKET, unix.SO_RCVBUF, ueventReceiveBufferSize)
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addr := &unix.SockaddrNetlink{
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Family: unix.AF_NETLINK,
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Groups: 1,
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}
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err = unix.Bind(fd, addr)
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if err != nil {
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_ = unix.Close(fd)
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return nil, err
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}
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return &ueventListener{file: os.NewFile(uintptr(fd), "netlink-uevent")}, nil
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}
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func (l *ueventListener) Close() error {
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return l.file.Close()
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}
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func (l *ueventListener) WaitUSBEvent() error {
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rawConn, err := l.file.SyscallConn()
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if err != nil {
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return err
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}
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var buf [16384]byte
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for {
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var (
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n int
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from unix.Sockaddr
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recvErr error
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)
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err = rawConn.Read(func(fd uintptr) bool {
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for {
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n, from, recvErr = unix.Recvfrom(int(fd), buf[:], 0)
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if recvErr == unix.EINTR {
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continue
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}
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return recvErr != unix.EAGAIN
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}
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})
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if err != nil {
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return err
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}
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if recvErr == unix.ENOBUFS {
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return nil
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}
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if recvErr != nil {
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return recvErr
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}
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if source, ok := from.(*unix.SockaddrNetlink); ok && source.Pid != 0 {
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continue
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}
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if isUSBDeviceUEvent(buf[:n]) {
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return nil
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}
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}
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}
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var (
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usbSubsystemMarker = []byte("\x00SUBSYSTEM=usb\x00")
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usbDeviceTypeMarker = []byte("\x00DEVTYPE=usb_device\x00")
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)
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func isUSBDeviceUEvent(raw []byte) bool {
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return bytes.Contains(raw, usbSubsystemMarker) && bytes.Contains(raw, usbDeviceTypeMarker)
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}
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