[PATCH v2 29/36] fs: add do_mknodat() helper and ksys_mknod() wrapper; remove in-kernel calls to syscall

[Dominik Brodowski]

Using the fs-internal do_mknodat() helper allows us to get rid of
fs-internal calls to the sys_mknodat() syscall.

Introducing the ksys_mknod() wrapper allows us to avoid the in-kernel
calls to sys_mknod() syscall.

Cc: Al Viro <v...@zeniv.linux.org.uk>
Cc: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Dominik Brodowski <li...@dominikbrodowski.net>
---
 fs/internal.h            |  2 ++
 fs/namei.c               | 12 +++++++++---
 include/linux/syscalls.h |  9 +++++++++
 init/do_mounts.h         |  2 +-
 init/initramfs.c         |  2 +-
 init/noinitramfs.c       |  2 +-
 6 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/fs/internal.h b/fs/internal.h
index a3f04ca2a08b..4f0b67054c54 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -55,6 +55,8 @@ extern void __init chrdev_init(void);
 extern int user_path_mountpoint_at(int, const char __user *, unsigned int, 
struct path *);
 extern int vfs_path_lookup(struct dentry *, struct vfsmount *,
                           const char *, unsigned int, struct path *);
+long do_mknodat(int dfd, const char __user *filename, umode_t mode,
+               unsigned int dev);
 long do_mkdirat(int dfd, const char __user *pathname, umode_t mode);
 long do_rmdir(int dfd, const char __user *pathname);
 long do_unlinkat(int dfd, struct filename *name);
diff --git a/fs/namei.c b/fs/namei.c
index e15da92209d5..8459a18cdd18 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3728,8 +3728,8 @@ static int may_mknod(umode_t mode)
        }
 }
 
-SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, 
mode,
-               unsigned, dev)
+long do_mknodat(int dfd, const char __user *filename, umode_t mode,
+               unsigned int dev)
 {
        struct dentry *dentry;
        struct path path;
@@ -3772,9 +3772,15 @@ SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, 
filename, umode_t, mode,
        return error;
 }
 
+SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, 
mode,
+               unsigned int, dev)
+{
+       return do_mknodat(dfd, filename, mode, dev);
+}
+
 SYSCALL_DEFINE3(mknod, const char __user *, filename, umode_t, mode, unsigned, 
dev)
 {
-       return sys_mknodat(AT_FDCWD, filename, mode, dev);
+       return do_mknodat(AT_FDCWD, filename, mode, dev);
 }
 
 int vfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 882c7fad2b68..a003ffedff52 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -1005,4 +1005,13 @@ static inline long ksys_symlink(const char __user 
*oldname,
        return do_symlinkat(oldname, AT_FDCWD, newname);
 }
 
+extern long do_mknodat(int dfd, const char __user *filename, umode_t mode,
+                      unsigned int dev);
+
+static inline long ksys_mknod(const char __user *filename, umode_t mode,
+                             unsigned int dev)
+{
+       return do_mknodat(AT_FDCWD, filename, mode, dev);
+}
+
 #endif
diff --git a/init/do_mounts.h b/init/do_mounts.h
index 401f90ee1eeb..0bb0806de4ce 100644
--- a/init/do_mounts.h
+++ b/init/do_mounts.h
@@ -17,7 +17,7 @@ extern int root_mountflags;
 static inline int create_dev(char *name, dev_t dev)
 {
        ksys_unlink(name);
-       return sys_mknod(name, S_IFBLK|0600, new_encode_dev(dev));
+       return ksys_mknod(name, S_IFBLK|0600, new_encode_dev(dev));
 }
 
 static inline u32 bstat(char *name)
diff --git a/init/initramfs.c b/init/initramfs.c
index cd9571a113b6..2972ed0ab399 100644
--- a/init/initramfs.c
+++ b/init/initramfs.c
@@ -359,7 +359,7 @@ static int __init do_name(void)
        } else if (S_ISBLK(mode) || S_ISCHR(mode) ||
                   S_ISFIFO(mode) || S_ISSOCK(mode)) {
                if (maybe_link() == 0) {
-                       sys_mknod(collected, mode, rdev);
+                       ksys_mknod(collected, mode, rdev);
                        sys_chown(collected, uid, gid);
                        sys_chmod(collected, mode);
                        do_utime(collected, mtime);
diff --git a/init/noinitramfs.c b/init/noinitramfs.c
index a08a9d937e60..f4bad8436c93 100644
--- a/init/noinitramfs.c
+++ b/init/noinitramfs.c
@@ -33,7 +33,7 @@ static int __init default_rootfs(void)
        if (err < 0)
                goto out;
 
-       err = sys_mknod((const char __user __force *) "/dev/console",
+       err = ksys_mknod((const char __user __force *) "/dev/console",
                        S_IFCHR | S_IRUSR | S_IWUSR,
                        new_encode_dev(MKDEV(5, 1)));
        if (err < 0)
-- 
2.16.2