[PATCH] flags parameter for linkat

I'm currently at the POSIX meeting and one thing covered was the
incompatibility of Linux's link() with the POSIX definition.  The name.
Linux does not follow symlinks, POSIX requires it does.

Even if somebody thinks this is a good default behavior we cannot change this
because it would break the ABI.  But the fact remains that some application
might want this behavior.

We have one chance to help implementing this without breaking the behavior.
 For this we could use the new linkat interface which would need a new
flags parameter.  If the new parameter is AT_SYMLINK_FOLLOW the new
behavior could be invoked.

I do not want to introduce such a patch now.  But we could add the
parameter now, just don't use it.  The patch below would do this.  Can we
get this late patch applied before the release more or less fixes the
syscall API?

Signed-off-by: Ulrich Drepper <[email protected]>
Signed-off-by: Ralf Baechle <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

arch/mips/kernel/scall32-o32.S

@@ -626,7 +626,7 @@ einval:	li	v0, -EINVAL
 	sys	sys_fstatat64		4
 	sys	sys_unlinkat		3
 	sys	sys_renameat		4	/* 4295 */
-	sys	sys_linkat		4
+	sys	sys_linkat		5
 	sys	sys_symlinkat		3
 	sys	sys_readlinkat		4
 	sys	sys_fchmodat		3

arch/s390/kernel/compat_wrapper.S

@@ -1552,6 +1552,7 @@ sys_linkat_wrapper:
 	llgtr	%r3,%r3			# const char *
 	lgfr	%r4,%r4			# int
 	llgtr	%r5,%r5			# const char *
+	lgfr	%r6,%r6			# int
 	jg	sys_linkat
 
 	.globl sys_symlinkat_wrapper

fs/namei.c

@@ -2224,13 +2224,17 @@ int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_de
  * and other special files.  --ADM
  */
 asmlinkage long sys_linkat(int olddfd, const char __user *oldname,
-			   int newdfd, const char __user *newname)
+			   int newdfd, const char __user *newname,
+			   int flags)
 {
 	struct dentry *new_dentry;
 	struct nameidata nd, old_nd;
 	int error;
 	char * to;
 
+	if (flags != 0)
+		return -EINVAL;
+
 	to = getname(newname);
 	if (IS_ERR(to))
 		return PTR_ERR(to);
@@ -2263,7 +2267,7 @@ asmlinkage long sys_linkat(int olddfd, const char __user *oldname,
 
 asmlinkage long sys_link(const char __user *oldname, const char __user *newname)
 {
-	return sys_linkat(AT_FDCWD, oldname, AT_FDCWD, newname);
+	return sys_linkat(AT_FDCWD, oldname, AT_FDCWD, newname, 0);
 }
 
 /*

include/linux/syscalls.h

@@ -543,7 +543,7 @@ asmlinkage long sys_unlinkat(int dfd, const char __user * pathname, int flag);
 asmlinkage long sys_symlinkat(const char __user * oldname,
 			      int newdfd, const char __user * newname);
 asmlinkage long sys_linkat(int olddfd, const char __user *oldname,
-			   int newdfd, const char __user *newname);
+			   int newdfd, const char __user *newname, int flags);
 asmlinkage long sys_renameat(int olddfd, const char __user * oldname,
 			     int newdfd, const char __user * newname);
 asmlinkage long sys_futimesat(int dfd, char __user *filename,