fs/compat: optional preadv64/pwrite64 compat system calls

The preadv64/pwrite64 have been implemented for the x32 ABI, in order
to allow passing 64 bit arguments from user space without splitting
them into two 32 bit parameters, like it would be necessary for usual
compat tasks.
Howevert these two system calls are only being used for the x32 ABI,
so add __ARCH_WANT_COMPAT defines for these two compat syscalls and
make these two only visible for x86.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

fs/read_write.c

@@ -982,9 +982,9 @@ COMPAT_SYSCALL_DEFINE3(readv, compat_ulong_t, fd,
 	return ret;
 }
 
-COMPAT_SYSCALL_DEFINE4(preadv64, unsigned long, fd,
-		const struct compat_iovec __user *,vec,
-		unsigned long, vlen, loff_t, pos)
+static long __compat_sys_preadv64(unsigned long fd,
+				  const struct compat_iovec __user *vec,
+				  unsigned long vlen, loff_t pos)
 {
 	struct fd f;
 	ssize_t ret;
@@ -1001,12 +1001,22 @@ COMPAT_SYSCALL_DEFINE4(preadv64, unsigned long, fd,
 	return ret;
 }
 
+#ifdef __ARCH_WANT_COMPAT_SYS_PREADV64
+COMPAT_SYSCALL_DEFINE4(preadv64, unsigned long, fd,
+		const struct compat_iovec __user *,vec,
+		unsigned long, vlen, loff_t, pos)
+{
+	return __compat_sys_preadv64(fd, vec, vlen, pos);
+}
+#endif
+
 COMPAT_SYSCALL_DEFINE5(preadv, compat_ulong_t, fd,
 		const struct compat_iovec __user *,vec,
 		compat_ulong_t, vlen, u32, pos_low, u32, pos_high)
 {
 	loff_t pos = ((loff_t)pos_high << 32) | pos_low;
-	return compat_sys_preadv64(fd, vec, vlen, pos);
+
+	return __compat_sys_preadv64(fd, vec, vlen, pos);
 }
 
 static size_t compat_writev(struct file *file,
@@ -1049,9 +1059,9 @@ COMPAT_SYSCALL_DEFINE3(writev, compat_ulong_t, fd,
 	return ret;
 }
 
-COMPAT_SYSCALL_DEFINE4(pwritev64, unsigned long, fd,
-		const struct compat_iovec __user *,vec,
-		unsigned long, vlen, loff_t, pos)
+static long __compat_sys_pwritev64(unsigned long fd,
+				   const struct compat_iovec __user *vec,
+				   unsigned long vlen, loff_t pos)
 {
 	struct fd f;
 	ssize_t ret;
@@ -1068,12 +1078,22 @@ COMPAT_SYSCALL_DEFINE4(pwritev64, unsigned long, fd,
 	return ret;
 }
 
+#ifdef __ARCH_WANT_COMPAT_SYS_PWRITEV64
+COMPAT_SYSCALL_DEFINE4(pwritev64, unsigned long, fd,
+		const struct compat_iovec __user *,vec,
+		unsigned long, vlen, loff_t, pos)
+{
+	return __compat_sys_pwritev64(fd, vec, vlen, pos);
+}
+#endif
+
 COMPAT_SYSCALL_DEFINE5(pwritev, compat_ulong_t, fd,
 		const struct compat_iovec __user *,vec,
 		compat_ulong_t, vlen, u32, pos_low, u32, pos_high)
 {
 	loff_t pos = ((loff_t)pos_high << 32) | pos_low;
-	return compat_sys_pwritev64(fd, vec, vlen, pos);
+
+	return __compat_sys_pwritev64(fd, vec, vlen, pos);
 }
 #endif