um: generalize os_rcv_fd

Change os_rcv_fd() to os_rcv_fd_msg() that can more generally
receive any number of FDs in any kind of message.

Link: https://patch.msgid.link/20240702192118.40b78b2bfe4e.Ic6ec12d72630e5bcae1e597d6bd5c6f29f441563@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

arch/um/drivers/port_kern.c

@@ -45,15 +45,17 @@ struct connection {
 static irqreturn_t pipe_interrupt(int irq, void *data)
 {
 	struct connection *conn = data;
-	int fd;
+	int n_fds = 1, fd = -1;
+	ssize_t ret;
 
-	fd = os_rcv_fd(conn->socket[0], &conn->helper_pid);
-	if (fd < 0) {
-		if (fd == -EAGAIN)
+	ret = os_rcv_fd_msg(conn->socket[0], &fd, n_fds, &conn->helper_pid,
+			    sizeof(conn->helper_pid));
+	if (ret != sizeof(conn->helper_pid)) {
+		if (ret == -EAGAIN)
 			return IRQ_NONE;
 
-		printk(KERN_ERR "pipe_interrupt : os_rcv_fd returned %d\n",
-		       -fd);
+		printk(KERN_ERR "pipe_interrupt : os_rcv_fd_msg returned %zd\n",
+		       ret);
 		os_close_file(conn->fd);
 	}
 

arch/um/drivers/xterm.c

@@ -156,7 +156,7 @@ static int xterm_open(int input, int output, int primary, void *d,
 	new = xterm_fd(fd, &data->helper_pid);
 	if (new < 0) {
 		err = new;
-		printk(UM_KERN_ERR "xterm_open : os_rcv_fd failed, err = %d\n",
+		printk(UM_KERN_ERR "xterm_open : xterm_fd failed, err = %d\n",
 		       -err);
 		goto out_kill;
 	}

arch/um/drivers/xterm_kern.c

@@ -21,12 +21,19 @@ struct xterm_wait {
 static irqreturn_t xterm_interrupt(int irq, void *data)
 {
 	struct xterm_wait *xterm = data;
-	int fd;
+	int fd = -1, n_fds = 1;
+	ssize_t ret;
 
-	fd = os_rcv_fd(xterm->fd, &xterm->pid);
-	if (fd == -EAGAIN)
+	ret = os_rcv_fd_msg(xterm->fd, &fd, n_fds,
+			    &xterm->pid, sizeof(xterm->pid));
+	if (ret == -EAGAIN)
 		return IRQ_NONE;
 
+	if (ret < 0)
+		fd = ret;
+	else if (ret != sizeof(xterm->pid))
+		fd = -EMSGSIZE;
+
 	xterm->new_fd = fd;
 	complete(&xterm->ready);
 

arch/um/include/shared/os.h

@@ -165,7 +165,8 @@ extern int os_create_unix_socket(const char *file, int len, int close_on_exec);
 extern int os_shutdown_socket(int fd, int r, int w);
 extern int os_dup_file(int fd);
 extern void os_close_file(int fd);
-extern int os_rcv_fd(int fd, int *helper_pid_out);
+ssize_t os_rcv_fd_msg(int fd, int *fds, unsigned int n_fds,
+		      void *data, size_t data_len);
 extern int os_connect_socket(const char *name);
 extern int os_file_type(char *file);
 extern int os_file_mode(const char *file, struct openflags *mode_out);

arch/um/kernel/ksyms.c

@@ -33,7 +33,7 @@ EXPORT_SYMBOL(os_shutdown_socket);
 EXPORT_SYMBOL(os_create_unix_socket);
 EXPORT_SYMBOL(os_connect_socket);
 EXPORT_SYMBOL(os_accept_connection);
-EXPORT_SYMBOL(os_rcv_fd);
+EXPORT_SYMBOL(os_rcv_fd_msg);
 EXPORT_SYMBOL(run_helper);
 EXPORT_SYMBOL(os_major);
 EXPORT_SYMBOL(os_minor);

arch/um/os-Linux/file.c

@@ -512,44 +512,47 @@ int os_shutdown_socket(int fd, int r, int w)
 	return 0;
 }
 
-int os_rcv_fd(int fd, int *helper_pid_out)
+/**
+ * os_rcv_fd_msg - receive message with (optional) FDs
+ * @fd: the FD to receive from
+ * @fds: the array for FDs to write to
+ * @n_fds: number of FDs to receive (@fds array size)
+ * @data: the message buffer
+ * @data_len: the size of the message to receive
+ *
+ * Receive a message with FDs.
+ *
+ * Returns: the size of the received message, or an error code
+ */
+ssize_t os_rcv_fd_msg(int fd, int *fds, unsigned int n_fds,
+		      void *data, size_t data_len)
 {
-	int new, n;
-	char buf[CMSG_SPACE(sizeof(new))];
-	struct msghdr msg;
+	char buf[CMSG_SPACE(sizeof(*fds) * n_fds)];
 	struct cmsghdr *cmsg;
-	struct iovec iov;
-
-	msg.msg_name = NULL;
-	msg.msg_namelen = 0;
-	iov = ((struct iovec) { .iov_base  = helper_pid_out,
-				.iov_len   = sizeof(*helper_pid_out) });
-	msg.msg_iov = &iov;
-	msg.msg_iovlen = 1;
-	msg.msg_control = buf;
-	msg.msg_controllen = sizeof(buf);
-	msg.msg_flags = 0;
+	struct iovec iov = {
+		.iov_base = data,
+		.iov_len = data_len,
+	};
+	struct msghdr msg = {
+		.msg_iov = &iov,
+		.msg_iovlen = 1,
+		.msg_control = buf,
+		.msg_controllen = sizeof(buf),
+	};
+	int n;
 
 	n = recvmsg(fd, &msg, 0);
 	if (n < 0)
 		return -errno;
-	else if (n != iov.iov_len)
-		*helper_pid_out = -1;
 
 	cmsg = CMSG_FIRSTHDR(&msg);
-	if (cmsg == NULL) {
-		printk(UM_KERN_ERR "rcv_fd didn't receive anything, "
-		       "error = %d\n", errno);
-		return -1;
-	}
-	if ((cmsg->cmsg_level != SOL_SOCKET) ||
-	    (cmsg->cmsg_type != SCM_RIGHTS)) {
-		printk(UM_KERN_ERR "rcv_fd didn't receive a descriptor\n");
-		return -1;
-	}
+	if (!cmsg ||
+	    cmsg->cmsg_level != SOL_SOCKET ||
+	    cmsg->cmsg_type != SCM_RIGHTS)
+		return n;
 
-	new = ((int *) CMSG_DATA(cmsg))[0];
-	return new;
+	memcpy(fds, CMSG_DATA(cmsg), cmsg->cmsg_len);
+	return n;
 }
 
 int os_create_unix_socket(const char *file, int len, int close_on_exec)