Why debugfs doesn't show crtime in nanoseconds?

Question

I am using:

debugfs -R 'stat <7473635>' /dev/sda7

to get the file creation time (crtime).

Inode: 7473635   Type: regular    Mode:  0664   Flags: 0x80000
Generation: 1874934325    Version: 0x00000000:00000001
User:  1000   Group:  1000   Size: 34
File ACL: 0    Directory ACL: 0
Links: 1   Blockcount: 8
Fragment:  Address: 0    Number: 0    Size: 0
 ctime: 0x55b65ebc:98040bc4 -- Mon Jul 27 22:09:24 2015
 atime: 0x55da0168:60b33f74 -- Sun Aug 23 22:52:48 2015
 mtime: 0x55b65ebc:98040bc4 -- Mon Jul 27 22:09:24 2015
crtime: 0x55b65ebc:970fe7cc -- Mon Jul 27 22:09:24 2015
Size of extra inode fields: 28
EXTENTS:
(0):29919781

Why am I not getting crtime in nanoseconds even though ext4 supports nanosecond resolution?

score 3 · Answer 1 · answered Aug 24 '15 at 16:58

It looks like debugfs does not yet support printing out the sub-second portion (the upper 30 bits of i_xtime_extra) of timestamps in its asctime-based format. From http://git.kernel.org/cgit/fs/ext2/e2fsprogs.git/tree/debugfs/debugfs.c :

if (is_large_inode && large_inode->i_extra_isize >= 24) {
        fprintf(out, "%s ctime: 0x%08x:%08x -- %s", prefix,
            inode->i_ctime, large_inode->i_ctime_extra,
            time_to_string(inode->i_ctime));
        fprintf(out, "%s atime: 0x%08x:%08x -- %s", prefix,
            inode->i_atime, large_inode->i_atime_extra,
            time_to_string(inode->i_atime));
        fprintf(out, "%s mtime: 0x%08x:%08x -- %s", prefix,
            inode->i_mtime, large_inode->i_mtime_extra,
            time_to_string(inode->i_mtime));
        fprintf(out, "%scrtime: 0x%08x:%08x -- %s", prefix,
            large_inode->i_crtime, large_inode->i_crtime_extra,
            time_to_string(large_inode->i_crtime));

Thanks for the link, but I've to accept @don_crissti's post as the answer because it provided the solution. — Ron, Aug 24 '15 at 17:28
Fair enough. At some point, I'll write a patch that takes the `i_*time_extra` field into account. The field provides not only nanosecond precision but also gives extended range for the date, by adding bits to `i_*time` to make it a 34-bit number. — Mark Plotnick, Aug 24 '15 at 18:45

score 3 · Accepted Answer · answered Aug 24 '15 at 17:11

It does show the timestamp (with nanoseconds precision) but in hex; it's the field after crtime:, e.g. in your output 0x55b65ebc:970fe7cc. The part after the colon is the nanoseconds.
This article gives more details and explains how to calculate the timestamp/nanoseconds. So, e.g. to convert the hex values to a timestamp a la stat you could run:

date -d @$(printf %d 0x55b65ebc).$(( $(printf %d 0x970fe7cc) / 4 )) +'%F %T.%N %z'

2015-07-27 19:39:24.633600499 +0300

Wow, thanks! After reading @Mark Plotnick's answer I was just about to ask what those hex meant! — Ron, Aug 24 '15 at 17:26

Why debugfs doesn't show crtime in nanoseconds?

2 Answers2