diff --git a/mount_linux.go b/mount_linux.go new file mode 100644 index 0000000..dfe70b5 --- /dev/null +++ b/mount_linux.go @@ -0,0 +1,116 @@ +package fuseshim + +import ( + "bufio" + "fmt" + "io" + "log" + "net" + "os" + "os/exec" + "sync" + "syscall" +) + +// Maximum file write size we are prepared to receive from the kernel. Linux +// appears to limit writes to 128 KiB. +const maxWrite = 128 * 1024 + +func lineLogger(wg *sync.WaitGroup, prefix string, r io.ReadCloser) { + defer wg.Done() + + scanner := bufio.NewScanner(r) + for scanner.Scan() { + switch line := scanner.Text(); line { + case `fusermount: failed to open /etc/fuse.conf: Permission denied`: + // Silence this particular message, it occurs way too + // commonly and isn't very relevant to whether the mount + // succeeds or not. + continue + default: + log.Printf("%s: %s", prefix, line) + } + } + if err := scanner.Err(); err != nil { + log.Printf("%s, error reading: %v", prefix, err) + } +} + +func mount(dir string, conf *mountConfig, ready chan<- struct{}, errp *error) (fusefd *os.File, err error) { + // linux mount is never delayed + close(ready) + + fds, err := syscall.Socketpair(syscall.AF_FILE, syscall.SOCK_STREAM, 0) + if err != nil { + return nil, fmt.Errorf("socketpair error: %v", err) + } + + writeFile := os.NewFile(uintptr(fds[0]), "fusermount-child-writes") + defer writeFile.Close() + + readFile := os.NewFile(uintptr(fds[1]), "fusermount-parent-reads") + defer readFile.Close() + + cmd := exec.Command( + "fusermount", + "-o", conf.getOptions(), + "--", + dir, + ) + cmd.Env = append(os.Environ(), "_FUSE_COMMFD=3") + + cmd.ExtraFiles = []*os.File{writeFile} + + var wg sync.WaitGroup + stdout, err := cmd.StdoutPipe() + if err != nil { + return nil, fmt.Errorf("setting up fusermount stderr: %v", err) + } + stderr, err := cmd.StderrPipe() + if err != nil { + return nil, fmt.Errorf("setting up fusermount stderr: %v", err) + } + + if err := cmd.Start(); err != nil { + return nil, fmt.Errorf("fusermount: %v", err) + } + wg.Add(2) + go lineLogger(&wg, "mount helper output", stdout) + go lineLogger(&wg, "mount helper error", stderr) + wg.Wait() + if err := cmd.Wait(); err != nil { + return nil, fmt.Errorf("fusermount: %v", err) + } + + c, err := net.FileConn(readFile) + if err != nil { + return nil, fmt.Errorf("FileConn from fusermount socket: %v", err) + } + defer c.Close() + + uc, ok := c.(*net.UnixConn) + if !ok { + return nil, fmt.Errorf("unexpected FileConn type; expected UnixConn, got %T", c) + } + + buf := make([]byte, 32) // expect 1 byte + oob := make([]byte, 32) // expect 24 bytes + _, oobn, _, _, err := uc.ReadMsgUnix(buf, oob) + scms, err := syscall.ParseSocketControlMessage(oob[:oobn]) + if err != nil { + return nil, fmt.Errorf("ParseSocketControlMessage: %v", err) + } + if len(scms) != 1 { + return nil, fmt.Errorf("expected 1 SocketControlMessage; got scms = %#v", scms) + } + scm := scms[0] + gotFds, err := syscall.ParseUnixRights(&scm) + if err != nil { + return nil, fmt.Errorf("syscall.ParseUnixRights: %v", err) + } + if len(gotFds) != 1 { + return nil, fmt.Errorf("wanted 1 fd; got %#v", gotFds) + } + f := os.NewFile(uintptr(gotFds[0]), "/dev/fuse") + return f, nil +}