init: add an init_dup helper

Add a simple helper to grab a reference to a file and install it at
the next available fd, and switch the early init code over to it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 12 insertions, 0 deletions

diff --git a/fs/init.c b/fs/init.c
index db5c48a85644..e9c320a48cf1 100644
--- a/fs/init.c
+++ b/fs/init.c
@@ -8,6 +8,7 @@
 #include <linux/namei.h>
 #include <linux/fs.h>
 #include <linux/fs_struct.h>
+#include <linux/file.h>
 #include <linux/init_syscalls.h>
 #include <linux/security.h>
 #include "internal.h"
@@ -251,3 +252,14 @@ int __init init_utimes(char *filename, struct timespec64 *ts)
 	path_put(&path);
 	return error;
 }
+
+int __init init_dup(struct file *file)
+{
+	int fd;
+
+	fd = get_unused_fd_flags(0);
+	if (fd < 0)
+		return fd;
+	fd_install(fd, get_file(file));
+	return 0;
+}