Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754644Ab1BMPuQ (ORCPT ); Sun, 13 Feb 2011 10:50:16 -0500 Received: from mail-vw0-f46.google.com ([209.85.212.46]:51205 "EHLO mail-vw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750932Ab1BMPuO (ORCPT ); Sun, 13 Feb 2011 10:50:14 -0500 MIME-Version: 1.0 From: Marti Raudsepp Date: Sun, 13 Feb 2011 17:49:42 +0200 Message-ID: Subject: btrfs: compression breaks cp and cross-FS mv, FS_IOC_FIEMAP bug? To: btrfs hackers , Kernel hackers Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2015 Lines: 55 Hi list! It seems I have found a serious regression in compressed btrfs in kernel 2.6.37. When creating a small file (less than the block size) and then cp/mv it to *another* file system, an appropriate number of zeroes gets written to the destination file. Case in point: % echo foobar > foobar % hexdump -C foobar 00000000 66 6f 6f 62 61 72 0a |foobar.| 00000007 % mv foobar /tmp % hexdump -C /tmp/foobar 00000000 00 00 00 00 00 00 00 |.......| 00000007 % cp foobar foobar2 % hexdump -C foobar2 00000000 00 00 00 00 00 00 00 |.......| 00000007 Via strace I found that mv doesn't even attempt to read anything: open("foobar", O_RDONLY|O_NOFOLLOW) = 3 fstat(3, {st_mode=S_IFREG|0664, st_size=7, ...}) = 0 open("/tmp/foobar", O_WRONLY|O_CREAT|O_EXCL, 0600) = 4 fstat(4, {st_mode=S_IFREG|0600, st_size=0, ...}) = 0 ioctl(3, FS_IOC_FIEMAP, 0x7fff62f6bfa0) = 0 write(4, "\0\0\0\0\0\0\0", 7) = 7 What's that, is FS_IOC_FIEMAP telling it that it's a sparse file? Compare with ext4: ioctl(3, FS_IOC_FIEMAP, 0x7fff2c576a90) = 0 lseek(3, 0, SEEK_SET) = 0 read(3, "foobar\n", 4096) = 7 write(4, "foobar\n", 7) = 7 I'm currently running on 2.6.37, x86_64 using Arch Linux -testing with coreutils 8.10. Filesystem is mounted from LVM2 to /usr/src with -o noatime,compress This only seems to occur with compressed file systems (either zlib or LZO). A person on IRC also reproduced the same problem in 2.6.28-rc. I'm pretty sure this used to work correctly around 2.6.35 or 2.6.36. This is 100% reproducible here. If anyone has trouble reproducing this, I can dig further and provide information as needed. Regards, Marti -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/