ext4 - getting at birth time (file create time) and getting/setting nanosecond time stamps and utime
adilger at sun.com
Tue Oct 20 18:44:08 MDT 2009
On 20-Oct-09, at 14:49, Steve French wrote:
> On Tue, Oct 20, 2009 at 3:33 PM, Andreas Dilger <adilger at sun.com>
>> For those users/admins that want to be able to change this (due to
>> Samba, or whatever), great, we can give them this ability, but for
>> users who do NOT want regular users to be able to change the file
>> creation timestamp, that should be possible as well.
> So, are we ready for Mingming or one of the ext4 developers to propose
> a patch for this via xattrs (I can do a similar one for cifs).
> Sounds like various have said:
> 1) xattrs instead of ioctl
> 2) get of create time allowed by default, but set of create time
A wildly untested/uncompiled patch is attached for purposes of
One issue that I've already come across is if we are storing a raw
we will get different xattrs on disk in the fallback case where the on-
inodes are not large enough to store the crtime inside the inode.
This version of the patch will fall back to storing the timespec on disk
in the supplied size/endianness as an xattr, but it definitely needs
handled more appropriately (endian/word size). It _would_ be nice to
a full 64-bit timespec on disk, but given that the in-inode format
handle 34 bits of seconds + 30 bits of nanoseconds, it isn't clear
the "fallback" should do better than that.
The main question is whether storing a "user.crtime" as an on-disk xattr
is a desirable fallback, or if this should just fail? Similarly, should
the lack of on-disk crtime return "0.0" as the creation time, or should
it return -ENODATA or similar?
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.
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