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Commit 9b32105e authored by Dominik Brodowski's avatar Dominik Brodowski
Browse files

kernel: add ksys_unshare() helper; remove in-kernel calls to sys_unshare() 

Using this helper allows us to avoid the in-kernel calls to the
sys_unshare() 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_unshare().

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>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: default avatarDominik Brodowski <linux@dominikbrodowski.net>
parent 70f68ee8

drivers/base/devtmpfs.c

+1 −1
Original line number Diff line number Diff line
@@ -380,7 +380,7 @@ static int devtmpfsd(void *p) 
{

	char options[] = "mode=0755";

	int *err = p;

	*err = sys_unshare(CLONE_NEWNS);

	*err = ksys_unshare(CLONE_NEWNS);

	if (*err)

		goto out;

	*err = ksys_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, options);

include/linux/syscalls.h

+1 −0
Original line number Diff line number Diff line
@@ -961,6 +961,7 @@ int ksys_ioctl(unsigned int fd, unsigned int cmd, unsigned long arg); 
off_t ksys_lseek(unsigned int fd, off_t offset, unsigned int whence);

ssize_t ksys_read(unsigned int fd, char __user *buf, size_t count);

void ksys_sync(void);

int ksys_unshare(unsigned long unshare_flags);



/*

 * The following kernel syscall equivalents are just wrappers to fs-internal

init/do_mounts_initrd.c

+1 −1
Original line number Diff line number Diff line
@@ -36,7 +36,7 @@ __setup("noinitrd", no_initrd); 


static int init_linuxrc(struct subprocess_info *info, struct cred *new)

{

	sys_unshare(CLONE_FS | CLONE_FILES);

	ksys_unshare(CLONE_FS | CLONE_FILES);

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

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

	ksys_dup(0);

kernel/fork.c

+6 −1
Original line number Diff line number Diff line
@@ -2354,7 +2354,7 @@ static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp 
 * constructed. Here we are modifying the current, active,

 * task_struct.

 */

SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)

int ksys_unshare(unsigned long unshare_flags)

{

	struct fs_struct *fs, *new_fs = NULL;

	struct files_struct *fd, *new_fd = NULL;
@@ -2470,6 +2470,11 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags) 
	return err;

}



SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)

{

	return ksys_unshare(unshare_flags);

}



/*

 *	Helper to unshare the files of the current task.

 *	We don't want to expose copy_files internals to