[PATCH] fstatat64 support

The *at patches introduced fstatat and, due to inusfficient research, I
used the newfstat functions generally as the guideline. The result is that
on 32-bit platforms we don't have all the information needed to implement
fstatat64.

This patch modifies the code to pass up 64-bit information if
__ARCH_WANT_STAT64 is defined. I renamed the syscall entry point to make
this clear. Other archs will continue to use the existing code. On x86-64
the compat code is implemented using a new sys32_ function. this is what
is done for the other stat syscalls as well.

This patch might break some other archs (those which define
__ARCH_WANT_STAT64 and which already wired up the syscall). Yet others
might need changes to accomodate the compatibility mode. I really don't
want to do that work because all this stat handling is a mess (more so in
glibc, but the kernel is also affected). It should be done by the arch
maintainers. I'll provide some stand-alone test shortly. Those who are
eager could compile glibc and run 'make check' (no installation needed).

The patch below has been tested on x86 and x86-64.

Signed-off-by: Ulrich Drepper <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/i386/kernel/syscall_table.S

···
 	.long sys_mknodat
 	.long sys_fchownat
 	.long sys_futimesat
-	.long sys_newfstatat		/* 300 */
+	.long sys_fstatat64		/* 300 */
 	.long sys_unlinkat
 	.long sys_renameat
 	.long sys_linkat

arch/x86_64/ia32/ia32entry.S

···
 	.quad sys_mknodat
 	.quad sys_fchownat
 	.quad compat_sys_futimesat
-	.quad compat_sys_newfstatat	/* 300 */
+	.quad sys32_fstatat		/* 300 */
 	.quad sys_unlinkat
 	.quad sys_renameat
 	.quad sys_linkat

arch/x86_64/ia32/sys_ia32.c

···
 	return ret;
 }
 
+asmlinkage long
+sys32_fstatat(unsigned int dfd, char __user *filename,
+	      struct stat64 __user* statbuf, int flag)
+{
+	struct kstat stat;
+	int error = -EINVAL;
+
+	if ((flag & ~AT_SYMLINK_NOFOLLOW) != 0)
+		goto out;
+
+	if (flag & AT_SYMLINK_NOFOLLOW)
+		error = vfs_lstat_fd(dfd, filename, &stat);
+	else
+		error = vfs_stat_fd(dfd, filename, &stat);
+
+	if (!error)
+		error = cp_stat64(statbuf, &stat);
+
+out:
+	return error;
+}
+
 /*
  * Linux/i386 didn't use to be able to handle more than
  * 4 system call parameters, so these system calls used a memory

fs/stat.c

···
 	return error;
 }
 
+#ifndef __ARCH_WANT_STAT64
 asmlinkage long sys_newfstatat(int dfd, char __user *filename,
 				struct stat __user *statbuf, int flag)
 {
···
 out:
 	return error;
 }
+#endif
 
 asmlinkage long sys_newfstat(unsigned int fd, struct stat __user *statbuf)
 {
···
 	return error;
 }
 
+asmlinkage long sys_fstatat64(int dfd, char __user *filename,
+			       struct stat64 __user *statbuf, int flag)
+{
+	struct kstat stat;
+	int error = -EINVAL;
+
+	if ((flag & ~AT_SYMLINK_NOFOLLOW) != 0)
+		goto out;
+
+	if (flag & AT_SYMLINK_NOFOLLOW)
+		error = vfs_lstat_fd(dfd, filename, &stat);
+	else
+		error = vfs_stat_fd(dfd, filename, &stat);
+
+	if (!error)
+		error = cp_new_stat64(&stat, statbuf);
+
+out:
+	return error;
+}
 #endif /* __ARCH_WANT_STAT64 */
 
 void inode_add_bytes(struct inode *inode, loff_t bytes)

include/asm-i386/unistd.h

···
 #define __NR_mknodat		297
 #define __NR_fchownat		298
 #define __NR_futimesat		299
-#define __NR_newfstatat		300
+#define __NR_fstatat64		300
 #define __NR_unlinkat		301
 #define __NR_renameat		302
 #define __NR_linkat		303

include/asm-x86_64/ia32_unistd.h

···
 #define __NR_ia32_mknodat		297
 #define __NR_ia32_fchownat		298
 #define __NR_ia32_futimesat		299
-#define __NR_ia32_newfstatat		300
+#define __NR_ia32_fstatat64		300
 #define __NR_ia32_unlinkat		301
 #define __NR_ia32_renameat		302
 #define __NR_ia32_linkat		303

include/linux/syscalls.h

···
 			   int mode);
 asmlinkage long sys_newfstatat(int dfd, char __user *filename,
 			       struct stat __user *statbuf, int flag);
+asmlinkage long sys_fstatat64(int dfd, char __user *filename,
+			       struct stat64 __user *statbuf, int flag);
 asmlinkage long sys_readlinkat(int dfd, const char __user *path, char __user *buf,
 			       int bufsiz);
 asmlinkage long compat_sys_futimesat(unsigned int dfd, char __user *filename,