From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f68.google.com ([74.125.82.68]:34051 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725898AbeICMXY (ORCPT ); Mon, 3 Sep 2018 08:23:24 -0400 Date: Mon, 3 Sep 2018 10:04:22 +0200 From: Pali =?utf-8?B?Um9ow6Fy?= To: OGAWA Hirofumi Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH] fat: Relax checks for sector size and media type Message-ID: <20180903080422.ta3clnhr5bobv6il@pali> References: <20180902131932.11558-1-pali.rohar@gmail.com> <87bm9ft5h5.fsf@mail.parknet.co.jp> <20180903074005.7e3guj24ksq2l44c@pali> <874lf7t3gg.fsf@mail.parknet.co.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <874lf7t3gg.fsf@mail.parknet.co.jp> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Monday 03 September 2018 17:01:03 OGAWA Hirofumi wrote: > Pali Rohár writes: > > >> Just relaxing validation doesn't work. The block layer doesn't support > >> smaller than 512, and lager than PAGE_SIZE. (And in specification, fat > >> doesn't support lager than 4096.) > > > > Hi! I just sent this patch for discussion, with links to (now open > > source) Windows implementation. I guess that Windows driver > > implementation is more "authoritative" then Microsoft's own > > specification. It is known that Windows implementation does not match > > Microsoft specification. > > > > I know at least 3 FAT specifications (MS EFI FAT, MS/SD card FAT, > > ECMA-107) and you are right that Microsoft's one does not allow sector > > sizes larger then 4096. > > > > If there is limitation by block layer, then: > > > > 1) Why we do not check for PAGE_SIZE? > > That source seems to check power_of_2(size) and 128 <= size <= > 4096. Rather why do you want to support larger than 4096? Or I'm missing > something? I looked into (Linux) mkfs.fat and it supports formatting disk also with sector size > 4096. Therefore I thought it may be good idea for ability to mount and use it (on Linux). I could check what other operating system would do with FAT sector size larger then 4096. > > 2) Is check in fat driver really needed (if block layer checks it)? > > Yes, isolating block layer error and fat format error to be better error > report. Ok. -- Pali Rohár pali.rohar@gmail.com