From: Alex Tomas Subject: Re: [PATCH 1/1 version2] Extent overlap bugfix in ext4 Date: Thu, 04 Jan 2007 14:37:40 +0300 Message-ID: References: <20070102090909.GA20503@amitarora.in.ibm.com> <1167788128.4197.17.camel@dyn9047017103.beaverton.ibm.com> <20070103060601.GB5343@amitarora.in.ibm.com> <20070104085407.GC5345@amitarora.in.ibm.com> <20070104112707.GB15920@amitarora.in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Alex Tomas , Mingming Cao , linux-ext4@vger.kernel.org, suparna@in.ibm.com Return-path: Received: from fe02.tochka.ru ([62.5.255.22]:39668 "EHLO umail.ru" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S964795AbXADLhz (ORCPT ); Thu, 4 Jan 2007 06:37:55 -0500 To: "Amit K. Arora" In-Reply-To: <20070104112707.GB15920@amitarora.in.ibm.com> (Amit K. Arora's message of "Thu\, 4 Jan 2007 16\:57\:07 +0530") Sender: linux-ext4-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org >>>>> Amit K Arora (AKA) writes: AT> I'm also not sure we need ext4_ext_find_extent() here. AKA> Do you mean ext4_ext_next_allocated_block() above ? We anyhow have to AKA> call find_extent() to get the possible neighbouring extent. no, I exactly meant ext4_ext_find_extent(). it's expensive compared to ext4_ext_next_allocated_block(). and if I understand right, you don't need whole extent, you just need to know next allocated block, which can be retrieved from index even. this is what ext4_ext_next_allocated_block() does. AT> there are two possibilities: >> AT> 1) extent in found path covers block(s) before requested ones AT> then ext4_ext_next_allocated_block(path) can be used >> AT> 2) extent in found path covers block(s) after request ones AT> then ee_block from that extent can be used. AKA> You are right. In the case the requested block(s) lie within a hole, when AKA> this hole starts from the begining of the file, this will be true. i.e., AKA> find_blocks() will return the extent after the requested block(s). In all AKA> other cases, it will return the extent before the requested block(s) AKA> (assuming there is no existing extent which covers the start of the AKA> requested blocks). existing blocks are to be handled properly in get_blocks(): /* if found extent covers block, simply return it */ if (iblock >= ee_block && iblock < ee_block + ee_len) { newblock = iblock - ee_block + ee_start; /* number of remaining blocks in the extent */ allocated = ee_len - (iblock - ee_block); ext_debug("%d fit into %lu:%d -> %llu\n", (int) iblock, ee_block, ee_len, newblock); ext4_ext_put_in_cache(inode, ee_block, ee_len, ee_start, EXT4_EXT_CACHE_EXTENT); AKA> Will change the code accordingly to handle this corner case. Thanks for AKA> pointing this out ! my pleasure. thanks, Alex