Hi All, I hope this is the correct place for ext4 / e2fsprogs bug reports. I think this is a bug. As per the title, I've discovered sparse files appear corrupt after running "e2fsck -E bmap2extent" on a filesystem I'm migrating. Tested with kernel.org 4.10.15 and 4.11.1, using e2fsprogs-1.43.4 on an x86_64 system. In short, I'm carrying out a data migration from a snapshot of an ext3 filesystem to new storage, then expanding the filesystem, converting (in place) to ext4 (as per https://ext4.wiki.kernel.org/index.php/UpgradeToExt4), before de-fragmenting the new filesystem with e4defrag. As part of the testing, I created md5sums of all the source files. After a "dry run" of the migration, a minority of files (approx 30 out of 1095578 inodes) were found to be corrupt (ie the md5sum had changed). I repeated the process a second time, checking the md5sums after each step of the migration. It appears the corruption occurs after running "e2fsck -E bmap2extent -fy" on the newly converted ext4 filesystem. The one thing I can find in common is all the affected files are sparse files. Here's a few example files: linux-2.6.30/arch/x86/kernel/acpi/realmode/wakeup.bin: FAILED linux-2.6.30/arch/x86/boot/compressed/vmlinux.bin: FAILED marc.old/.mozilla/firefox/ecyfs7l9.default/Cache/_CACHE_003_: FAILED Linux4.x/linux-4.10.12/arch/x86/realmode/rm/realmode.bin: FAILED Linux4.x/linux-4.10.1/arch/x86/realmode/rm/realmode.bin: FAILED They are all definitely sparse files, eg: $ ls -l Linux4.x/linux-4.10.1/arch/x86/realmode/rm/realmode.bin -rwxr-xr-x 1 marc users 21080 Mar 8 12:03 Linux4.x/linux-4.10.1/arch/x86/realmode/rm/realmode.bin $ du -k Linux4.x/linux-4.10.1/arch/x86/realmode/rm/realmode.bin 16 Linux4.x/linux-4.10.1/arch/x86/realmode/rm/realmode.bin $ du --apparent -k Linux4.x/linux-4.10.1/arch/x86/realmode/rm/realmode.bin 21 Linux4.x/linux-4.10.1/arch/x86/realmode/rm/realmode.bin Would you agree this is a bug? As I understand it, reading from an "unpopulated" region of a sparse file should return all zeros - so the md5sum should be the same before and after migration. I'm happy to provide more details and do testing if required. I have an offline copy of the source filesystem so can run the migration again. Let me know if there's anything you need. Thanks & Kind Regards, Marc
