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

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

Introducing the ksys_link() wrapper allows us to avoid the in-kernel
calls to sys_link() 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_link().

In the near future, the only fs-external user of ksys_link() should be
converted to use vfs_link() instead.

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 11:34:53 +01:00
parent 87c4e19262
commit 46ea89eb65
4 changed files with 21 additions and 4 deletions
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2
fs/internal.h
View File

@ -62,6 +62,8 @@ long do_rmdir(int dfd, const char __user *pathname);
long do_unlinkat(int dfd, struct filename *name);
long do_symlinkat(const char __user *oldname, int newdfd,
const char __user *newname);
int do_linkat(int olddfd, const char __user *oldname, int newdfd,
const char __user *newname, int flags);
/*
* namespace.c

12
fs/namei.c
View File

@ -4250,8 +4250,8 @@ EXPORT_SYMBOL(vfs_link);
* with linux 2.0, and to avoid hard-linking to directories
* and other special files. --ADM
*/
SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
int, newdfd, const char __user *, newname, int, flags)
int do_linkat(int olddfd, const char __user *oldname, int newdfd,
const char __user *newname, int flags)
{
struct dentry *new_dentry;
struct path old_path, new_path;
@ -4315,9 +4315,15 @@ SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
return error;
}
SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
int, newdfd, const char __user *, newname, int, flags)
{
return do_linkat(olddfd, oldname, newdfd, newname, flags);
}
SYSCALL_DEFINE2(link, const char __user *, oldname, const char __user *, newname)
{
return sys_linkat(AT_FDCWD, oldname, AT_FDCWD, newname, 0);
return do_linkat(AT_FDCWD, oldname, AT_FDCWD, newname, 0);
}
/**

9
include/linux/syscalls.h
View File

@ -997,4 +997,13 @@ static inline long ksys_mknod(const char __user *filename, umode_t mode,
return do_mknodat(AT_FDCWD, filename, mode, dev);
}
extern int do_linkat(int olddfd, const char __user *oldname, int newdfd,
const char __user *newname, int flags);
static inline long ksys_link(const char __user *oldname,
const char __user *newname)
{
return do_linkat(AT_FDCWD, oldname, AT_FDCWD, newname, 0);
}
#endif

2
init/initramfs.c
View File

@ -306,7 +306,7 @@ static int __init maybe_link(void)
if (nlink >= 2) {
char *old = find_link(major, minor, ino, mode, collected);
if (old)
return (sys_link(old, collected) < 0) ? -1 : 1;
return (ksys_link(old, collected) < 0) ? -1 : 1;
}
return 0;
}