fs: remove ksys_dup()

ksys_dup() is used only at one place in the kernel, namely to duplicate
fd 0 of /dev/console to stdout and stderr. The same functionality can be
achieved by using functions already available within the kernel namespace.
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>

fs/file.c

@@ -960,7 +960,7 @@ SYSCALL_DEFINE2(dup2, unsigned int, oldfd, unsigned int, newfd)
 	return ksys_dup3(oldfd, newfd, 0);
 }
 
-int ksys_dup(unsigned int fildes)
+SYSCALL_DEFINE1(dup, unsigned int, fildes)
 {
 	int ret = -EBADF;
 	struct file *file = fget_raw(fildes);
@@ -975,11 +975,6 @@ int ksys_dup(unsigned int fildes)
 	return ret;
 }
 
-SYSCALL_DEFINE1(dup, unsigned int, fildes)
-{
-	return ksys_dup(fildes);
-}
-
 int f_dupfd(unsigned int from, struct file *file, unsigned flags)
 {
 	int err;

include/linux/syscalls.h

@@ -1232,7 +1232,6 @@ asmlinkage long sys_ni_syscall(void);
  */
 
 int ksys_umount(char __user *name, int flags);
-int ksys_dup(unsigned int fildes);
 int ksys_chroot(const char __user *filename);
 ssize_t ksys_write(unsigned int fd, const char __user *buf, size_t count);
 int ksys_chdir(const char __user *filename);

init/main.c

@@ -93,6 +93,7 @@
 #include <linux/rodata_test.h>
 #include <linux/jump_label.h>
 #include <linux/mem_encrypt.h>
+#include <linux/file.h>
 
 #include <asm/io.h>
 #include <asm/bugs.h>
@@ -1157,13 +1158,26 @@ static int __ref kernel_init(void *unused)
 
 void console_on_rootfs(void)
 {
-	/* Open the /dev/console as stdin, this should never fail */
-	if (ksys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
-		pr_err("Warning: unable to open an initial console.\n");
+	struct file *file;
+	unsigned int i;
+
+	/* Open /dev/console in kernelspace, this should never fail */
+	file = filp_open("/dev/console", O_RDWR, 0);
+	if (!file)
+		goto err_out;
+
+	/* create stdin/stdout/stderr, this should never fail */
+	for (i = 0; i < 3; i++) {
+		if (f_dupfd(i, file, 0) != i)
+			goto err_out;
+	}
 
-	/* create stdout/stderr */
-	(void) ksys_dup(0);
-	(void) ksys_dup(0);
+	return;
+
+err_out:
+	/* no panic -- this might not be fatal */
+	pr_err("Warning: unable to open an initial console.\n");
+	return;
 }
 
 static noinline void __init kernel_init_freeable(void)