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fs: add ksys_chdir() helper; remove in-kernel calls to sys_chdir()

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Using this helper allows us to avoid the in-kernel calls to the sys_chdir()
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_chdir().

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>
This commit is contained in:
Dominik Brodowski 2018-03-11 11:34:46 +01:00
parent e7a3e8b2ed
commit 447016e968
5 changed files with 13 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/base/devtmpfs.c
View File

@ -386,7 +386,7 @@ static int devtmpfsd(void *p)
*err = ksys_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, options);
if (*err)
goto out;
sys_chdir("/.."); /* will traverse into overmounted root */
ksys_chdir("/.."); /* will traverse into overmounted root */
ksys_chroot(".");
complete(&setup_done);
while (1) {

7
fs/open.c
View File

@ -431,7 +431,7 @@ SYSCALL_DEFINE2(access, const char __user *, filename, int, mode)
return sys_faccessat(AT_FDCWD, filename, mode);
}
SYSCALL_DEFINE1(chdir, const char __user *, filename)
int ksys_chdir(const char __user *filename)
{
struct path path;
int error;
@ -457,6 +457,11 @@ out:
return error;
}
SYSCALL_DEFINE1(chdir, const char __user *, filename)
{
return ksys_chdir(filename);
}
SYSCALL_DEFINE1(fchdir, unsigned int, fd)
{
struct fd f = fdget_raw(fd);

1
include/linux/syscalls.h
View File

@ -952,5 +952,6 @@ int ksys_umount(char __user *name, int flags);
int ksys_dup(unsigned int fildes);
int ksys_chroot(const char __user *filename);
ssize_t ksys_write(unsigned int fd, const char __user *buf, size_t count);
int ksys_chdir(const char __user *filename);
#endif

2
init/do_mounts.c
View File

@ -367,7 +367,7 @@ static int __init do_mount_root(char *name, char *fs, int flags, void *data)
if (err)
return err;
sys_chdir("/root");
ksys_chdir("/root");
s = current->fs->pwd.dentry->d_sb;
ROOT_DEV = s->s_dev;
printk(KERN_INFO

8
init/do_mounts_initrd.c
View File

@ -42,7 +42,7 @@ static int init_linuxrc(struct subprocess_info *info, struct cred *new)
ksys_dup(0);
ksys_dup(0);
/* move initrd over / and chdir/chroot in initrd root */
sys_chdir("/root");
ksys_chdir("/root");
ksys_mount(".", "/", NULL, MS_MOVE, NULL);
ksys_chroot(".");
sys_setsid();
@ -61,7 +61,7 @@ static void __init handle_initrd(void)
/* mount initrd on rootfs' /root */
mount_block_root("/dev/root.old", root_mountflags & ~MS_RDONLY);
sys_mkdir("/old", 0700);
sys_chdir("/old");
ksys_chdir("/old");
/* try loading default modules from initrd */
load_default_modules();
@ -86,11 +86,11 @@ static void __init handle_initrd(void)
ksys_chroot("..");
if (new_decode_dev(real_root_dev) == Root_RAM0) {
sys_chdir("/old");
ksys_chdir("/old");
return;
}
sys_chdir("/");
ksys_chdir("/");
ROOT_DEV = new_decode_dev(real_root_dev);
mount_root();