From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alvin Abitria Subject: LBA starting address alignment from struct request Date: Sun, 7 Dec 2014 11:49:41 +0800 Message-ID: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 To: linux-fsdevel@vger.kernel.org Return-path: Received: from mail-wi0-f194.google.com ([209.85.212.194]:33803 "EHLO mail-wi0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751320AbaLGDtm (ORCPT ); Sat, 6 Dec 2014 22:49:42 -0500 Received: by mail-wi0-f194.google.com with SMTP id l15so913984wiw.9 for ; Sat, 06 Dec 2014 19:49:41 -0800 (PST) Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Hello, Currently doing block drivers. I've noticed during my tests that if my platform are RHEL6.x/CentOS6.x my struct request's starting LBA/sector is always aligned to 8 (e.g. 0, 8, 0x100, 0x2508, etc.) which is actually desirable for my designed driver. It seems the struct requests are always aligned there. On the other hand, if I test on some older systems like Oracle 5.6, the starting LBA for struct requests there seems not to be aligned to 8 - most cases the LBA is offseted (e.g. 0x2507, 300f, 0x95bd500f, etc.) My block queue settings and even looking from sysfs shows that my logical block size and physical block size are 512 and 512, respectively. So I don't think it has something to do with 4kB sectors. What could be the setting that triggered such behaviour? Is there a request queue or gendisk setting that controls this that I may not be aware of? Or is this up to the FS layer? Hopefully someone can point it out. Thanks!