os: handle EINTR from open(2).

The man page for sigaction(2) on OS X doesn't guarantee that SA_RESTART
will work for open(2) on regular files:

    The affected system calls include open(2), read(2), write(2),
    sendto(2), recvfrom(2), sendmsg(2) and recvmsg(2) on a
    communications channel or a slow device (such as a terminal, but not
    a regular file) and during a wait(2) or ioctl(2).

I've never observed EINTR from open(2) for a traditional file system
such as HFS+, but it's easy to observe with a fuse file system that is
slightly slow (cf. https://goo.gl/UxsVgB). After this change, the
problem can no longer be reproduced when calling os.OpenFile.

Fixes #11180.

Change-Id: I967247430e20a7d29a285b3d76bf3498dc4773db
Reviewed-on: https://go-review.googlesource.com/14484
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/os/file_unix.go

@@ -90,8 +90,16 @@ func OpenFile(name string, flag int, perm FileMode) (*File, error) {
 		}
 	}
 
+retry:
 	r, e := syscall.Open(name, flag|syscall.O_CLOEXEC, syscallMode(perm))
 	if e != nil {
+		// On OS X, sigaction(2) doesn't guarantee that SA_RESTART will cause
+		// open(2) to be restarted for regular files. This is easy to reproduce on
+		// fuse file systems (see http://golang.org/issue/11180).
+		if e == syscall.EINTR {
+			goto retry
+		}
+
 		return nil, &PathError{"open", name, e}
 	}