fs: add do_mkdirat() helper and ksys_mkdir() wrapper; remove in-kernel calls to syscall

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

Introducing the ksys_mkdir() wrapper allows us to avoid the in-kernel calls
to the sys_mkdir() syscall. The ksys_ prefix denotes that this function is
meant as a drop-in replacement for the syscall. In particular, it uses the
same calling convention as sys_mkdir().

This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.net

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>

1 files changed, 7 insertions, 2 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 8545151f74e9..dcf506227509 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3803,7 +3803,7 @@ int vfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
 }
 EXPORT_SYMBOL(vfs_mkdir);
 
-SYSCALL_DEFINE3(mkdirat, int, dfd, const char __user *, pathname, umode_t, mode)
+long do_mkdirat(int dfd, const char __user *pathname, umode_t mode)
 {
 	struct dentry *dentry;
 	struct path path;
@@ -3828,9 +3828,14 @@ retry:
 	return error;
 }
 
+SYSCALL_DEFINE3(mkdirat, int, dfd, const char __user *, pathname, umode_t, mode)
+{
+	return do_mkdirat(dfd, pathname, mode);
+}
+
 SYSCALL_DEFINE2(mkdir, const char __user *, pathname, umode_t, mode)
 {
-	return sys_mkdirat(AT_FDCWD, pathname, mode);
+	return do_mkdirat(AT_FDCWD, pathname, mode);
 }
 
 int vfs_rmdir(struct inode *dir, struct dentry *dentry)