linux-ext4 - Re: Garbage returned in nanosecond component of timestamps

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Message-ID: <4CE77E74.2070006@redhat.com>
Date:	Sat, 20 Nov 2010 01:53:24 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Jordan Russell <jr-list-2010@....to>
CC:	linux-ext4@...r.kernel.org
Subject: Re: Garbage returned in nanosecond component of timestamps

On 11/20/10 12:22 AM, Jordan Russell wrote:
> [Fedora 14 with vendor kernel 2.6.35.6-48.fc14.i686.PAE]
> 
> When nanosecond timestamp resolution isn't supported on an ext4
> partition (inode size = 128), stat() appears to be returning
> uninitialized garbage in the nanosecond component of timestamps.
> 
> See the following tests.
> Expected: All timestamps should end with '.0000000000'.
> Actual: '.0026721629' popping up on a different file each time.
> 
>> # tune2fs -l /dev/md0 | fgrep 'Inode size'
>> Inode size:               128
>> # echo 3 >/proc/sys/vm/drop_caches
>> # find / -xdev -type f -printf '%t - %p\n' | fgrep -v '.0000000000'
>> Wed Nov  4 16:53:20.0026721629 2009 - /boot/oldconfigs/config-2.6.27.38-170.2.113.fc10.i686.PAE
>> # echo 3 >/proc/sys/vm/drop_caches
>> # find / -xdev -type f -printf '%t - %p\n' | fgrep -v '.0000000000'
>> Thu Nov  8 20:38:30.0026721629 2007 - /boot/oldconfigs/config-2.6.23.1-49.fc8PAE
>> # echo 3 >/proc/sys/vm/drop_caches
>> # find / -xdev -type f -printf '%t - %p\n' | fgrep -v '.0000000000'
>> Thu Aug 12 17:44:51.0026721629 2010 - /lib/firmware/emi26/bitstream.fw
>> # echo 3 >/proc/sys/vm/drop_caches
>> # find / -xdev -type f -printf '%t - %p\n' | fgrep -v '.0000000000'
>> Thu Aug 12 17:44:51.0026721629 2010 - /lib/firmware/slicoss/gbdownload.sys
>> # echo 3 >/proc/sys/vm/drop_caches
>> # find / -xdev -type f -printf '%t - %p\n' | fgrep -v '.0000000000'
>> Fri Nov  5 01:16:32.0026721629 2010 - /boot/grub/e2fs_stage1_5
> 
> 
> Shouldn't EXT4_INODE_GET_XTIME zero out tv_nsec when EXT4_FITS_IN_INODE
> evaluates to false...?

Yep I think so, good catch...

-Eric

>> #define EXT4_INODE_GET_XTIME(xtime, inode, raw_inode)                          \
>> do {                                                                           \
>>         (inode)->xtime.tv_sec = (signed)le32_to_cpu((raw_inode)->xtime);       \
>>         if (EXT4_FITS_IN_INODE(raw_inode, EXT4_I(inode), xtime ## _extra))     \
>>                 ext4_decode_extra_time(&(inode)->xtime,                        \
>>                                        raw_inode->xtime ## _extra);            \
>> } while (0)
> 

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