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-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html