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fs: add ksys_umount() helper; remove in-kernel call to sys_umount()

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Using this helper allows us to avoid the in-kernel call to the sys_umount()
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 ksys_umount().

In the near future, the only fs-external caller of ksys_umount() should be
converted to call do_umount() directly. Then, ksys_umount() can be moved
within sys_umount() 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: Dominik Brodowski <linux@dominikbrodowski.net>
This commit is contained in:
Dominik Brodowski 2018-03-11 11:34:40 +01:00
parent 312db1aa1d
commit 3a18ef5c1b
3 changed files with 9 additions and 3 deletions
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9
fs/namespace.c
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@ -1680,7 +1680,7 @@ static inline bool may_mandlock(void)
* unixes. Our API is identical to OSF/1 to avoid making a mess of AMD
*/
SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
int ksys_umount(char __user *name, int flags)
{
struct path path;
struct mount *mnt;
@ -1720,6 +1720,11 @@ SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
return retval;
}
SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
{
return ksys_umount(name, flags);
}
#ifdef __ARCH_WANT_SYS_OLDUMOUNT
/*
@ -1727,7 +1732,7 @@ SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
*/
SYSCALL_DEFINE1(oldumount, char __user *, name)
{
return sys_umount(name, 0);
return ksys_umount(name, 0);
}
#endif

1
include/linux/syscalls.h
View File

@ -948,5 +948,6 @@ 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);
#endif

2
init/do_mounts_initrd.c
View File

@ -105,7 +105,7 @@ static void __init handle_initrd(void)
else
printk("failed\n");
printk(KERN_NOTICE "Unmounting old root\n");
sys_umount("/old", MNT_DETACH);
ksys_umount("/old", MNT_DETACH);
printk(KERN_NOTICE "Trying to free ramdisk memory ... ");
if (fd < 0) {
error = fd;