lib: Address https://v.io/i/1220

- reverts https://v.io/c/20483
- changes v23test to not share a bin dir across test main's
(bin dir is still shared across tests within a given test
main, but that's safe since "go test" will not run such
tests concurrently by default)
- changes v23test.StartRootMountTable and
v23test.StartSyncbase to use gosh.Shell.FuncCmd
(refactoring syncbased and mounttabled as needed to make
this possible)

A side effect of this change is that tests should run much
faster, because for the common case of tests that previously
used StartRootMountTable and/or StartSyncbase, but didn't
directly call BuildGoPkg, we'll no longer build Go packages
during test execution.

MultiPart: 2/5

Change-Id: Iba81f1db56ca21f2d887e26496d7a87ad288b076

Author: asadovsky

gosh/shell.go

@@ -150,7 +150,11 @@ func (sh *Shell) Wait() {
 	sh.handleError(sh.wait())
 }
 
-// Move moves a file.
+// Move moves a file from 'oldpath' to 'newpath'. It first attempts os.Rename;
+// if that fails, it copies 'oldpath' to 'newpath', then deletes 'oldpath'.
+// Requires that 'newpath' does not exist, and that the parent directory of
+// 'newpath' does exist. Currently only supports moving an individual file;
+// moving a directory is not yet supported.
 func (sh *Shell) Move(oldpath, newpath string) {
 	sh.Ok()
 	sh.handleError(sh.move(oldpath, newpath))
@@ -340,7 +344,7 @@ func (sh *Shell) wait() error {
 	return res
 }
 
-func copyFile(from, to string) error {
+func copyFile(to, from string) error {
 	fi, err := os.Stat(from)
 	if err != nil {
 		return err
@@ -363,18 +367,33 @@ func copyFile(from, to string) error {
 }
 
 func (sh *Shell) move(oldpath, newpath string) error {
-	var err error
-	if err = os.Rename(oldpath, newpath); err != nil {
-		// Concurrent, same-directory rename operations sometimes fail on certain
-		// filesystems, so we retry once after a random backoff.
-		time.Sleep(time.Duration(rand.Int63n(1000)) * time.Millisecond)
-		err = os.Rename(oldpath, newpath)
-	}
-	// If the error was a LinkError, try copying the file over.
-	if _, ok := err.(*os.LinkError); !ok {
+	fi, err := os.Stat(oldpath)
+	if err != nil {
 		return err
 	}
-	if err := copyFile(oldpath, newpath); err != nil {
+	if fi.Mode().IsDir() {
+		return errors.New("gosh: moving a directory is not yet supported")
+	}
+	if _, err := os.Stat(newpath); !os.IsNotExist(err) {
+		return errors.New("gosh: destination file must not exist")
+	}
+	if _, err := os.Stat(filepath.Dir(newpath)); err != nil {
+		if os.IsNotExist(err) {
+			return errors.New("gosh: destination file's parent directory must exist")
+		}
+		return err
+	}
+	if err := os.Rename(oldpath, newpath); err == nil {
+		return nil
+	}
+	// Concurrent, same-directory rename operations sometimes fail on certain
+	// systems, so we retry once after a random backoff.
+	time.Sleep(time.Duration(rand.Int63n(1000)) * time.Millisecond)
+	if err := os.Rename(oldpath, newpath); err == nil {
+		return nil
+	}
+	// Try copying the file over.
+	if err := copyFile(newpath, oldpath); err != nil {
 		return err
 	}
 	return os.Remove(oldpath)
@@ -540,6 +559,9 @@ var calledInitMain = false
 // parent process, it returns immediately with no effect. In a child process for
 // a Shell.FuncCmd command, it runs the specified function, then exits.
 func InitMain() {
+	if calledInitMain {
+		panic("gosh: already called gosh.InitMain")
+	}
 	calledInitMain = true
 	s := os.Getenv(envInvocation)
 	if s == "" {
@@ -629,5 +651,6 @@ func buildGoPkg(sh *Shell, binDir, pkg string, flags ...string) (string, error)
 	if err := sh.move(tempBinPath, binPath); err != nil {
 		return "", err
 	}
+	sh.tb.Logf("Built executable: %s\n", binPath)
 	return binPath, nil
 }