comparison mercurial/cext/osutil.c @ 49275:c6a3243567b6

chg: replace mercurial.util.recvfds() by simpler pure Python implementation

On Python 3, we have socket.socket.recvmsg(). This makes it possible to receive
FDs in pure Python code. The new code behaves like the previous
implementations, except that it’s more strict about the format of the ancillary
data. This works because we know in which format the FDs are passed.

Because the code is (and always has been) specific to chg (payload is 1 byte,
number of passed FDs is limited) and we now have only one implementation and
the code is very short, I decided to stop exposing a function in
mercurial.util.

Note on terminology: The SCM_RIGHTS mechanism is used to share open file
descriptions to another process over a socket. The sending side passes an array
of file descriptors and the receiving side receives an array of file
descriptors. The file descriptors are different in general on both sides but
refer to the same open file descriptions. The two terms are often conflated,
even in the official documentation. That’s why I used “FD” above, which could
mean both “file descriptor” and “file description”.

49273:34020d1f1635

bail:
	Py_DECREF(stats);
	return NULL;
}

/*
 * recvfds() simply does not release GIL during blocking io operation because
 * command server is known to be single-threaded.
 *
 * Old systems such as Solaris don't provide CMSG_LEN, msg_control, etc.
 * Currently, recvfds() is not supported on these platforms.
 */
#ifdef CMSG_LEN

static ssize_t recvfdstobuf(int sockfd, int **rfds, void *cbuf, size_t cbufsize)
{
	char dummy[1];
	struct iovec iov = {dummy, sizeof(dummy)};
	struct msghdr msgh = {0};
	struct cmsghdr *cmsg;

	msgh.msg_iov = &iov;
	msgh.msg_iovlen = 1;
	msgh.msg_control = cbuf;
	msgh.msg_controllen = (socklen_t)cbufsize;
	if (recvmsg(sockfd, &msgh, 0) < 0)
		return -1;

	for (cmsg = CMSG_FIRSTHDR(&msgh); cmsg;
	     cmsg = CMSG_NXTHDR(&msgh, cmsg)) {
		if (cmsg->cmsg_level != SOL_SOCKET ||
		    cmsg->cmsg_type != SCM_RIGHTS)
			continue;
		*rfds = (int *)CMSG_DATA(cmsg);
		return (cmsg->cmsg_len - CMSG_LEN(0)) / sizeof(int);
	}

	*rfds = cbuf;
	return 0;
}

static PyObject *recvfds(PyObject *self, PyObject *args)
{
	int sockfd;
	int *rfds = NULL;
	ssize_t rfdscount, i;
	char cbuf[256];
	PyObject *rfdslist = NULL;

	if (!PyArg_ParseTuple(args, "i", &sockfd))
		return NULL;

	rfdscount = recvfdstobuf(sockfd, &rfds, cbuf, sizeof(cbuf));
	if (rfdscount < 0)
		return PyErr_SetFromErrno(PyExc_OSError);

	rfdslist = PyList_New(rfdscount);
	if (!rfdslist)
		goto bail;
	for (i = 0; i < rfdscount; i++) {
		PyObject *obj = PyLong_FromLong(rfds[i]);
		if (!obj)
			goto bail;
		PyList_SET_ITEM(rfdslist, i, obj);
	}
	return rfdslist;

bail:
	Py_XDECREF(rfdslist);
	return NULL;
}

#endif /* CMSG_LEN */

/* allow disabling setprocname via compiler flags */
#ifndef SETPROCNAME_USE_NONE
#if defined(HAVE_SETPROCTITLE)
/* setproctitle is the first choice - available in FreeBSD */
#define SETPROCNAME_USE_SETPROCTITLE

"On error, this function may raise either a WindowsError or an IOError."},
#else
	{"statfiles", (PyCFunction)statfiles, METH_VARARGS | METH_KEYWORDS,
	 "stat a series of files or symlinks\n"
"Returns None for non-existent entries and entries of other types.\n"},
#ifdef CMSG_LEN
	{"recvfds", (PyCFunction)recvfds, METH_VARARGS,
	 "receive list of file descriptors via socket\n"},
#endif
#ifndef SETPROCNAME_USE_NONE
	{"setprocname", (PyCFunction)setprocname, METH_VARARGS,
	 "set process title (best-effort)\n"},
#endif
#if defined(HAVE_BSD_STATFS) || defined(HAVE_LINUX_STATFS)

49275:c6a3243567b6

bail:
	Py_DECREF(stats);
	return NULL;
}

/* allow disabling setprocname via compiler flags */
#ifndef SETPROCNAME_USE_NONE
#if defined(HAVE_SETPROCTITLE)
/* setproctitle is the first choice - available in FreeBSD */
#define SETPROCNAME_USE_SETPROCTITLE

"On error, this function may raise either a WindowsError or an IOError."},
#else
	{"statfiles", (PyCFunction)statfiles, METH_VARARGS | METH_KEYWORDS,
	 "stat a series of files or symlinks\n"
"Returns None for non-existent entries and entries of other types.\n"},
#ifndef SETPROCNAME_USE_NONE
	{"setprocname", (PyCFunction)setprocname, METH_VARARGS,
	 "set process title (best-effort)\n"},
#endif
#if defined(HAVE_BSD_STATFS) || defined(HAVE_LINUX_STATFS)