um: harddog: fix modular build

Since we no longer (want to) export any libc symbols the
_user portions of any drivers need to be built into image
rather than the module. I missed this for the watchdog.
Fix the watchdog accordingly.

Reported-by: kernel test robot <[e-mail]>
Signed-off-by: Johannes Berg <[e-mail]>
Signed-off-by: Richard Weinberger <[e-mail]>

arch/um/drivers/Makefile

···
 hostaudio-objs := hostaudio_kern.o
 ubd-objs := ubd_kern.o ubd_user.o
 port-objs := port_kern.o port_user.o
-harddog-objs := harddog_kern.o harddog_user.o
+harddog-objs := harddog_kern.o
+harddog-builtin-$(CONFIG_UML_WATCHDOG) := harddog_user.o harddog_user_exp.o
 rtc-objs := rtc_kern.o rtc_user.o
 
 LDFLAGS_pcap.o = $(shell $(CC) $(KBUILD_CFLAGS) -print-file-name=libpcap.a)
···
 obj-$(CONFIG_TTY_CHAN) += tty.o 
 obj-$(CONFIG_XTERM_CHAN) += xterm.o xterm_kern.o
 obj-$(CONFIG_UML_WATCHDOG) += harddog.o
+obj-y += $(harddog-builtin-y) $(harddog-builtin-m)
 obj-$(CONFIG_BLK_DEV_COW_COMMON) += cow_user.o
 obj-$(CONFIG_UML_RANDOM) += random.o
 obj-$(CONFIG_VIRTIO_UML) += virtio_uml.o

arch/um/drivers/harddog.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef UM_WATCHDOG_H
+#define UM_WATCHDOG_H
+
+int start_watchdog(int *in_fd_ret, int *out_fd_ret, char *sock);
+void stop_watchdog(int in_fd, int out_fd);
+int ping_watchdog(int fd);
+
+#endif /* UM_WATCHDOG_H */

arch/um/drivers/harddog_kern.c

···
 #include <linux/spinlock.h>
 #include <linux/uaccess.h>
 #include "mconsole.h"
+#include "harddog.h"
 
 MODULE_LICENSE("GPL");
 
···
 /*
  *	Allow only one person to hold it open
  */
-
-extern int start_watchdog(int *in_fd_ret, int *out_fd_ret, char *sock);
 
 static int harddog_open(struct inode *inode, struct file *file)
 {
···
 	return err;
 }
 
-extern void stop_watchdog(int in_fd, int out_fd);
-
 static int harddog_release(struct inode *inode, struct file *file)
 {
 	/*
···
 
 	return 0;
 }
-
-extern int ping_watchdog(int fd);
 
 static ssize_t harddog_write(struct file *file, const char __user *data, size_t len,
 			     loff_t *ppos)

arch/um/drivers/harddog_user.c

···
 #include <unistd.h>
 #include <errno.h>
 #include <os.h>
+#include "harddog.h"
 
 struct dog_data {
 	int stdin_fd;

arch/um/drivers/harddog_user_exp.c

···
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/export.h>
+#include "harddog.h"
+
+#if IS_MODULE(CONFIG_UML_WATCHDOG)
+EXPORT_SYMBOL(start_watchdog);
+EXPORT_SYMBOL(stop_watchdog);
+EXPORT_SYMBOL(ping_watchdog);
+#endif