From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kara Subject: Re: [PATCH] ext3: fix trim length underflow with small trim length. Date: Wed, 19 Jan 2011 12:39:21 +0100 Message-ID: <20110119113921.GA4246@quack.suse.cz> References: <1295430550-8978-1-git-send-email-tm@tao.ma> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Tao Ma , linux-ext4@vger.kernel.org, Jan Kara To: Lukas Czerner Return-path: Received: from cantor2.suse.de ([195.135.220.15]:59963 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753636Ab1ASLjY (ORCPT ); Wed, 19 Jan 2011 06:39:24 -0500 Content-Disposition: inline In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-ID: On Wed 19-01-11 11:42:50, Lukas Czerner wrote: > On Wed, 19 Jan 2011, Tao Ma wrote: > > > From: Tao Ma > > > > We adjust 'len' with s_first_data_block - start in case of start is less > > than s_first_data_block, but it could underflow in case blocksize=1K, while > > fstrim_range.len=512 and fstrim_range.start = 0. In this case len happens > > to be underflow and in the end, although we are safe that last_group check > > will limit the trim to the whole volume, I am afraid that isn't what the user > > really want. > > > > So this patch fix it. It also adds a new variable s_first_data_block so that > > the 4 le32_to_cpu can be replaced with 1. > > Well, I just realized that what are we doing is not exactly what will > user expect. User does not really care where the first data block is. > What the user will expect is, to trim let's say first one gigabyte > of his filesystem, not gigabyte - first data block. > > So what I suggest is to always add first_data_block to > fstrim_range.start and do all the necessary checks for overflow. If no > one has any objections I'll put it to the patch. Well, since we speak about at most 1KB (s_first_data_block is non-zero only when blocksize == 1024 and in that case it is 1), I don't think it really matters and I don't mind whatever solution. What user expects is a bit hard to guess (whether he views 'start' as a start of the filesystem or a start of the device). Maybe the former makes a tad bit more sense but as I said I don't really care so since you're the author of the code I leave it up to you. Honza -- Jan Kara SUSE Labs, CR