From: Evgeniy Ivanov Subject: Re: ext2/ext3 different block_sizes/i_size/e2fsck question Date: Fri, 26 Mar 2010 01:43:35 +0300 Message-ID: References: <20100325015503.GJ2159@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: linux-ext4@vger.kernel.org To: tytso@mit.edu Return-path: Received: from mail-fx0-f223.google.com ([209.85.220.223]:54859 "EHLO mail-fx0-f223.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752192Ab0CYWnh convert rfc822-to-8bit (ORCPT ); Thu, 25 Mar 2010 18:43:37 -0400 Received: by fxm23 with SMTP id 23so1649710fxm.21 for ; Thu, 25 Mar 2010 15:43:35 -0700 (PDT) In-Reply-To: <20100325015503.GJ2159@thunk.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Thu, Mar 25, 2010 at 4:55 AM, wrote: > On Wed, Mar 24, 2010 at 10:27:24PM +0300, Evgeniy Ivanov wrote: >> >> Sorry for bothering list with my ext2 questions. >> I got into trouble with my ext2 implementation and filesystem with >> 1024 block size. Sometimes when I write files they're written >> correctly (md5sum is the same as original, i_size is correct either)= , >> but e2fsck changes i_size to another values (which breaks files). E.= g. >> 67445000->67446784 or 67445248->67446784. I see that new sizes are >> numbers of multiples of 1024. >> Strange thing is that I can't reproduce this problem with 2048 and >> 4096 block sizes. I thought the problem was in trash in unused part = of >> last block (actually it is zeroed), but then it would be reproduceab= le >> in fs with another block size. > > E2fsck will adjust i_size if it is smaller than the number of blocks > than you have allocated. =A0So in the case of 67445000->67446784, you= r > file probably had 65866 1k blocks, and since 67445000 is less than > (655865*1024)+1, e2fsck assumed that your i_size was wrong, and so it > asked for permission to fix it. > > Put another way, if you have 2 blocks in 1k file, and i_size is 1024, > it clearly must be wrong. =A0If it's 1025, maybe we're only using 1 b= yte > in the last block; but if i_size is less than or equal to 1024, then > why was the 2nd block allocated in the file in the first place? Thank you for your explanation. My problem was in miscalculation of first triple indirect block. I used following thing "triple_ind_s =3D doub_ind_s + pow(addr_in_block, 2)" and it was a bad idea to use pow() instead of multiplication or shifting. It was ok with gcc (and libc), but caused a problem with ACK (I get value of 1 less, thus each last double indirect block became a hole instead of data). Since that was both in reading and writing md5 sums were correct (and in Linux I checked them only after e2fsck). =46unny bug :) --=20 Evgeniy Ivanov -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html