[TUHS] When/how did ctime change from inode "creation" to "change" time?

[Kenneth Goodwin]

I would take that IF clause to mean
If ICHG SET then exhibit new behavior and create now means change for ctime
field
otherwise follow original logic of ctime as being original epoch  creation
date.

Ie both behaviors are supported and depend on a flag bit being set or
cleared

On Tue, Mar 11, 2025, 11:57 PM Warner Losh <imp at bsdimp.com> wrote:

> So I think  I have to disagree about what it means in v7, comments
> notwithstanding.
>
> iupdat() has:
>                 if(ip->i_flag&ICHG)
>                         dp->di_ctime = time;
>
> ICHG is set in unlink(), chmod(), chown() and utime() (maybe a few others,
> this was a quick peek).
>
> So even in v7, ctime means any changes to metadata / inode data. At least
> for some definition of "any".
>
> Btw, it looks like this was named IUPD in v6 and did similar things. In v6
> it is updated in iput when IUPD is set. But it looks like ctime and mtime
> are folded together. So v7 is the first edition that has ctime and the code
> implements any change to metadata from my reading.
>
> Warner
>
> On Tue, Mar 11, 2025 at 8:19 PM Theodore Ts'o <tytso at mit.edu> wrote:
>
>> As part of a discusion on the Linux kernel mailing list, there was an
>> assertion that ctime was orginally "creation time".
>>
>> From the v7 sources in TUHS, we can see:
>>
>> struct dinode
>> {
>>         unsigned short  di_mode;        /* mode and type of file */
>>         short   di_nlink;       /* number of links to file */
>>         short   di_uid;         /* owner's user id */
>>         short   di_gid;         /* owner's group id */
>>         off_t   di_size;        /* number of bytes in file */
>>         char    di_addr[40];    /* disk block addresses */
>>         time_t  di_atime;       /* time last accessed */
>>         time_t  di_mtime;       /* time last modified */
>>         time_t  di_ctime;       /* time created */
>> };
>>
>> ... although the v7 kernel sources does seem to update ctime when the
>> inode metadata changes, regardless of what the coment in
>> /usr/src/sys/h/ino.h might say.
>>
>> More interestingly, this comment seems to continue in newer versions
>> up to 3BSD, and then the comments becomes "change time" in BSD 4.2,
>> probably coincident with the File System Implementation?
>>
>> The best we can guess is that the change from "creation time" to
>> "inode change time" happened sometime between 1979 and 1982.  Does
>> anyone who was around can give the story about how and when this
>> happened?
>>
>>                                         - Ted
>>
>
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