Commit c7248321 authored by Dominik Brodowski's avatar Dominik Brodowski
Browse files

fs: add ksys_dup{,3}() helper; remove in-kernel calls to sys_dup{,3}() 

Using ksys_dup() and ksys_dup3() as helper functions allows us to
avoid the in-kernel calls to the sys_dup() and sys_dup3() syscalls.
The ksys_ prefix denotes that these functions are meant as a drop-in
replacement for the syscalls. In particular, they use the same
calling convention as sys_dup{,3}().

In the near future, the fs-external callers of ksys_dup{,3}() should be
converted to call do_dup2() directly. Then, ksys_dup{,3}() can be moved
within sys_dup{,3}() again.

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: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarDominik Brodowski <linux@dominikbrodowski.net>
parent 3a18ef5c

fs/file.c

+13 −3
Original line number Diff line number Diff line
@@ -870,7 +870,7 @@ out_unlock: 
	return err;

}



SYSCALL_DEFINE3(dup3, unsigned int, oldfd, unsigned int, newfd, int, flags)

static int ksys_dup3(unsigned int oldfd, unsigned int newfd, int flags)

{

	int err = -EBADF;

	struct file *file;
@@ -904,6 +904,11 @@ out_unlock: 
	return err;

}



SYSCALL_DEFINE3(dup3, unsigned int, oldfd, unsigned int, newfd, int, flags)

{

	return ksys_dup3(oldfd, newfd, flags);

}



SYSCALL_DEFINE2(dup2, unsigned int, oldfd, unsigned int, newfd)

{

	if (unlikely(newfd == oldfd)) { /* corner case */
@@ -916,10 +921,10 @@ SYSCALL_DEFINE2(dup2, unsigned int, oldfd, unsigned int, newfd) 
		rcu_read_unlock();

		return retval;

	}

	return sys_dup3(oldfd, newfd, 0);

	return ksys_dup3(oldfd, newfd, 0);

}



SYSCALL_DEFINE1(dup, unsigned int, fildes)

int ksys_dup(unsigned int fildes)

{

	int ret = -EBADF;

	struct file *file = fget_raw(fildes);
@@ -934,6 +939,11 @@ SYSCALL_DEFINE1(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

+1 −0
Original line number Diff line number Diff line
@@ -949,5 +949,6 @@ asmlinkage long sys_statx(int dfd, const char __user *path, unsigned flags, 
int ksys_mount(char __user *dev_name, char __user *dir_name, char __user *type,

	       unsigned long flags, void __user *data);

int ksys_umount(char __user *name, int flags);

int ksys_dup(unsigned int fildes);



#endif

init/do_mounts_initrd.c

+2 −2
Original line number Diff line number Diff line
@@ -39,8 +39,8 @@ static int init_linuxrc(struct subprocess_info *info, struct cred *new) 
	sys_unshare(CLONE_FS | CLONE_FILES);

	/* stdin/stdout/stderr for /linuxrc */

	sys_open("/dev/console", O_RDWR, 0);

	sys_dup(0);

	sys_dup(0);

	ksys_dup(0);

	ksys_dup(0);

	/* move initrd over / and chdir/chroot in initrd root */

	sys_chdir("/root");

	ksys_mount(".", "/", NULL, MS_MOVE, NULL);

init/main.c

+2 −2
Original line number Diff line number Diff line
@@ -1077,8 +1077,8 @@ static noinline void __init kernel_init_freeable(void) 
	if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)

		pr_err("Warning: unable to open an initial console.\n");



	(void) sys_dup(0);

	(void) sys_dup(0);

	(void) ksys_dup(0);

	(void) ksys_dup(0);

	/*

	 * check if there is an early userspace init.  If yes, let it do all

	 * the work

CRA Git | Maintained and supported by SUSTech CRA and CCSE