From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964896AbWAWTQW (ORCPT ); Mon, 23 Jan 2006 14:16:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964897AbWAWTQW (ORCPT ); Mon, 23 Jan 2006 14:16:22 -0500 Received: from mx1.redhat.com ([66.187.233.31]:64955 "EHLO mx1.redhat.com") by vger.kernel.org with ESMTP id S964896AbWAWTQW (ORCPT ); Mon, 23 Jan 2006 14:16:22 -0500 From: Jeff Moyer MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <17365.11127.860256.702246@segfault.boston.redhat.com> Date: Mon, 23 Jan 2006 14:16:07 -0500 To: linux-kernel@vger.kernel.org CC: akpm@osdl.org Subject: [patch] fix O_DIRECT read of last block in a sparse file X-Mailer: VM 7.17 under 21.4 (patch 15) "Security Through Obscurity" XEmacs Lucid Reply-To: jmoyer@redhat.com X-PGP-KeyID: 1F78E1B4 X-PGP-CertKey: F6FE 280D 8293 F72C 65FD 5A58 1FF8 A7CA 1F78 E1B4 X-PCLoadLetter: What the f**k does that mean? Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi, Currently, if you open a file O_DIRECT, truncate it to a size that is not a multiple of the disk block size, and then try to read the last block in the file, the read will return 0. The problem is in do_direct_IO, here: /* Handle holes */ if (!buffer_mapped(map_bh)) { char *kaddr; ... if (dio->block_in_file >= i_size_read(dio->inode)>>blkbits) { /* We hit eof */ page_cache_release(page); goto out; } We shift off any remaining bytes in the final block of the I/O, resulting in a 0-sized read. I've attached a patch that fixes this. I'm not happy about how ugly the math is getting, so suggestions are more than welcome. I've tested this with a simple program that performs the steps outlined for reproducing the problem above. Without the patch, we get a 0-sized result from read. With the patch, we get the correct return value from the short read. Thanks, Jeff Signed-off-by: Jeff Moyer --- linux-2.6.16-rc1-mm1/fs/direct-io.c.orig 2006-01-19 15:45:50.000000000 -0500 +++ linux-2.6.16-rc1-mm1/fs/direct-io.c 2006-01-19 16:09:33.000000000 -0500 @@ -857,6 +857,7 @@ do_holes: /* Handle holes */ if (!buffer_mapped(map_bh)) { char *kaddr; + loff_t i_size = i_size_read(dio->inode); /* AKPM: eargh, -ENOTBLK is a hack */ if (dio->rw == WRITE) { @@ -864,8 +865,10 @@ do_holes: return -ENOTBLK; } - if (dio->block_in_file >= - i_size_read(dio->inode)>>blkbits) { + /* Be sure to account for a partial block as + * the last block in the file */ + if (dio->block_in_file >= i_size >> blkbits && + !(i_size & ~((1<