mirror of
https://github.com/opencontainers/runc.git
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85 lines
2.4 KiB
Go
85 lines
2.4 KiB
Go
package libcontainer
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import (
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"fmt"
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"io"
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"os"
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"sync/atomic"
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"golang.org/x/sys/unix"
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)
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// syncSocket is a wrapper around a SOCK_SEQPACKET socket, providing
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// packet-oriented methods. This is needed because SOCK_SEQPACKET does not
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// allow for partial reads, but the Go stdlib treats it as a streamable source,
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// which ends up making things like json.Decoder hang forever if the packet is
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// bigger than the internal read buffer.
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type syncSocket struct {
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f *os.File
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closed atomic.Bool
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}
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func newSyncSocket(f *os.File) *syncSocket {
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return &syncSocket{f: f}
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}
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func (s *syncSocket) File() *os.File {
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return s.f
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}
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func (s *syncSocket) Close() error {
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// Even with errors from Close(), we have to assume the pipe was closed.
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s.closed.Store(true)
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return s.f.Close()
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}
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func (s *syncSocket) isClosed() bool {
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return s.closed.Load()
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}
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func (s *syncSocket) WritePacket(b []byte) (int, error) {
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return s.f.Write(b)
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}
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func (s *syncSocket) ReadPacket() ([]byte, error) {
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size, _, err := unix.Recvfrom(int(s.f.Fd()), nil, unix.MSG_TRUNC|unix.MSG_PEEK)
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if err != nil {
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return nil, fmt.Errorf("fetch packet length from socket: %w", err)
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}
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// We will only get a zero size if the socket has been closed from the
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// other end (otherwise recvfrom(2) will block until a packet is ready). In
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// addition, SOCK_SEQPACKET is treated as a stream source by Go stdlib so
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// returning io.EOF here is correct from that perspective too.
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if size == 0 {
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return nil, io.EOF
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}
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buf := make([]byte, size)
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n, err := s.f.Read(buf)
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if err != nil {
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return nil, err
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}
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if n != size {
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return nil, fmt.Errorf("packet read too short: expected %d byte packet but only %d bytes read", size, n)
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}
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return buf, nil
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}
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func (s *syncSocket) Shutdown(how int) error {
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if err := unix.Shutdown(int(s.f.Fd()), how); err != nil {
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return &os.PathError{Op: "shutdown", Path: s.f.Name() + " (sync pipe)", Err: err}
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}
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return nil
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}
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// newSyncSockpair returns a new SOCK_SEQPACKET unix socket pair to be used for
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// runc-init synchronisation.
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func newSyncSockpair(name string) (parent, child *syncSocket, err error) {
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fds, err := unix.Socketpair(unix.AF_LOCAL, unix.SOCK_SEQPACKET|unix.SOCK_CLOEXEC, 0)
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if err != nil {
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return nil, nil, err
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}
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parentFile := os.NewFile(uintptr(fds[1]), name+"-p")
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childFile := os.NewFile(uintptr(fds[0]), name+"-c")
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return newSyncSocket(parentFile), newSyncSocket(childFile), nil
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}
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