[S390] Wire up sys_fallocate.

This patch implements support of fallocate system call on s390(x)
platform.  A wrapper is added to address the issue which s390 ABI has with
the arguments of this system call.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/sys_s390.c

@@ -265,3 +265,23 @@ s390_fadvise64_64(struct fadvise64_64_args __user *args)
 		return -EFAULT;
 	return sys_fadvise64_64(a.fd, a.offset, a.len, a.advice);
 }
+
+#ifndef CONFIG_64BIT
+/*
+ * This is a wrapper to call sys_fallocate(). For 31 bit s390 the last
+ * 64 bit argument "len" is split into the upper and lower 32 bits. The
+ * system call wrapper in the user space loads the value to %r6/%r7.
+ * The code in entry.S keeps the values in %r2 - %r6 where they are and
+ * stores %r7 to 96(%r15). But the standard C linkage requires that
+ * the whole 64 bit value for len is stored on the stack and doesn't
+ * use %r6 at all. So s390_fallocate has to convert the arguments from
+ *   %r2: fd, %r3: mode, %r4/%r5: offset, %r6/96(%r15)-99(%r15): len
+ * to
+ *   %r2: fd, %r3: mode, %r4/%r5: offset, 96(%r15)-103(%r15): len
+ */
+asmlinkage long s390_fallocate(int fd, int mode, loff_t offset,
+			       u32 len_high, u32 len_low)
+{
+	return sys_fallocate(fd, mode, offset, ((u64)len_high << 32) | len_low);
+}
+#endif