Detect when a file has been recreated using a stat watcher

Graham Leggett minfrin at sharp.fm
Tue Dec 23 19:21:59 CET 2008


Marc Lehmann wrote:

> Absolutely. But the ctime likely changes on file creation, or the size, or
> something else (such as the inode number).
> 
> This all depend son how your logfiles get rotated - the file might get
> trucnated, deleted or somethign else might happen.

So I should be looking at the size of the file, rather than the ctime of 
the file?

>> My question is, is libev using the stat64 structure by way of comparison?
> 
> No. And it wouldn't help your case unless you require the logifle to be on
> a specific filesystem supporting higher resolution timestamps. And even
> then, the higher resolution might sitll just be centiseconds or so.
> 
> All this doesn't help you. The documentation (that you somehow fail to
> know, for inexplicable reasons) explains this case in mroe details and
> offers ways to implement this properly in your app.

Maybe I am looking at different documentation to you.

I am looking at the following URL:

http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod#code_ev_stat_code_did_the_file_attri

The headings I see are "ABI Issues (Largefile Support)", "Inotify and 
Kqueue", "stat () is a synchronous operation" and "The special problem 
of stat time resolution". The word "rotate" doesn't appear at all in the 
docs I am reading.

Is there some other docs that I should be reading but am not aware of?

>> Is there a cross platform method to determine file rotation, by looking  
>> at the attr and prev variables returned by a stat event?
> 
> Yes, but for some reason you claim it wouldn't work.

So far I was led to believe that ctime can be used to detect file 
rotation, but the manpage for stat, and the code that I have in testing 
contradict this.

Should I be using the file length instead?

Regards,
Graham
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