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

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

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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