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SubjectRe: [EXT4 set 3][PATCH 1/1] ext4 nanosecond timestamp
On Jul 04, 2007  12:06 +0530, 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.

I wasn't on the most recent concall, and I've forgotten the details of
any discussion on a previous concall.

Care really needs to be taken here that negative timestamps are handled
properly. We can take the sign bit from the inode i_*time, but then we
need to change the load/save of the extra time to use a shift of 31
instead of 32. If we overflow the epoch we have to ensure that the high
bits of the seconds is handled correctly.

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.

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