Commit 46ea89eb authored by Dominik Brodowski's avatar Dominik Brodowski
Browse files

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

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: default avatarDominik Brodowski <linux@dominikbrodowski.net>
parent 87c4e192

fs/internal.h

+2 −0
Original line number Diff line number Diff line
@@ -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

fs/namei.c

+9 −3
Original line number Diff line number Diff line
@@ -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 @@ out: 
	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);

}



/**

include/linux/syscalls.h

+9 −0
Original line number Diff line number Diff line
@@ -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

init/initramfs.c

+1 −1
Original line number Diff line number Diff line
@@ -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;

}

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