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SubjectRe: [EXT4 set 3][PATCH 1/1] ext4 nanosecond timestamp


Aneesh Kumar K.V wrote:
>
>
> Mingming Cao wrote:
>> On Tue, 2007-07-03 at 15:58 +0530, Kalpak Shah wrote:
>>> On Sun, 2007-07-01 at 03:36 -0400, Mingming Cao wrote:
>>>> +
>>>> +#define EXT4_INODE_GET_XTIME(xtime, inode,
>>>> raw_inode) \
>>>> +do { \
>>>> + (inode)->xtime.tv_sec =
>>>> 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)
>>>> +
>>>> +#define EXT4_EINODE_GET_XTIME(xtime, einode,
>>>> raw_inode) \
>>>> +do { \
>>>> + if (EXT4_FITS_IN_INODE(raw_inode, einode, xtime)) \
>>>> + (einode)->xtime.tv_sec =
>>>> le32_to_cpu((raw_inode)->xtime); \
>>>> + if (EXT4_FITS_IN_INODE(raw_inode, einode, xtime ##
>>>> _extra)) \
>>>> + ext4_decode_extra_time(&(einode)->xtime, \
>>>> + raw_inode->xtime ## _extra); \
>>>> +} while (0)
>>>> +
>>> This nanosecond patch seems to be missing the fix below which is
>>> required for http://bugzilla.kernel.org/show_bug.cgi?id=5079
>>>
>>> If the timestamp is set to before epoch i.e. a negative timestamp
>>> then the file may have its date set into the future on 64-bit
>>> systems. So when the timestamp is read it must be cast as signed.
>>
>> Missed this one.
>> Thanks. Will update ext4 patch queue tonight with this fix.
>>
>>
>
>
> IIRC in the conference call it was decided to not to apply this patch.
> Andreas may be able to update better.
>


Looking at the git log i understand the core patch got applied to ext4 tree with the comment
from Andreas. So may be we can apply this patch also.


commit 4d7bf11d649c72621ca31b8ea12b9c94af380e63

Andreas says:

This patch is now treating timestamps with the high bit set as negative
times (before Jan 1, 1970). This means we lose 1/2 of the possible range
of timestamps (lopping off 68 years before unix timestamp overflow -
now only 30 years away :-) to handle the extremely rare case of setting
timestamps into the distant past.

If we are only interested in fixing the underflow case, we could just
limit the values to 0 instead of storing negative values. At worst this
will skew the timestamp by a few hours for timezones in the far east
(files would still show Jan 1, 1970 in "ls -l" output).

That said, it seems 32-bit systems (mine at least) allow files to be set
into the past (01/01/1907 works fine) so it seems this patch is bringing
the x86_64 behaviour into sync with other kernels.

On the plus side, we have a patch that is ready to add nanosecond timestamps
to ext3 and as an added bonus adds 2 high bits to the on-disk timestamp so
this extends the maximum date to 2242.

NOTE: The conference call i mentioned above is http://ext4.wiki.kernel.org/index.php/Ext4_Developer%27s_Conference_Call


-aneesh
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