link(2) EMLINK error behavior with --link-dest and --hard-links

[Karl O. Pinc]

Should I submit a bug?  Will you take a patch?

On 03/24/2012 11:11:47 PM, Karl O. Pinc wrote:
> Hi,
> 
> I'm having a problem using --link-dest and --hard-links when
> the fs hits the hard link limit (link(2) returns EMLINK).
> 
> Using rsync 3.0.7 an error is thrown and the target file is
> not created.  Glancing at git head it _looks_ like things
> could now be a little nicer.  Perhaps the target file is copied
> instead of hard linked when hardlinking fails -- I've not
> tested it.
> 
> Anyway, the behavior I desire when using both --link-dest and
> --hard-links and when running out of links is to get an error,
> but to "have the --link-dest fail".  In other words, the
> end result, for that particular target file, would be
> as if --link-dest was not specified.  This leaves the hard links
> in the source preserved in the target.  (At least an
> "exact copy" happens, which is more desirable than
> creating a copy at whatever point the hard link limit
> is reached and then hardlinking from that point forward --
> if that's what the git head code really does.)
> 
> Glancing over the code, it seems to me the way to do this 
> is to have the hard_link_one() return value indicate
> when failure is EMLINK.  This can then be tested for
> during the execution of finish_hard_link().  When
> link exhaustion is detected in finish_hard_link(),
> && link_dest, then report an error but also
> copy the source file and re-run
> finish_hard_link() to undo/fix-up the hard links
> already created.  This assumes that the
> hard links created so far can be overwritten and
> won't break things.  (And there needs to be some
> sort of flag to avoid an infinite loop
> should link exhaustion happen again.)
> 
> If this works there shouldn't be any performance
> impact unless hard links are exhausted.
> 
> I really don't understand how the code works,
> my suggestion could be completely wrong.
> I still wanted to supply a brain-dump here
> in case my suggestion is useful and to learn
> something from the feedback.
> 
> Regards,
> 
> Karl <kop at meme.com>
> Free Software:  "You don't pay back, you pay forward."
>                  -- Robert A. Heinlein
> 
> -- 
> Please use reply-all for most replies to avoid omitting the mailing
> list.
> To unsubscribe or change options: https://lists.samba.org/mailman/
> listinfo/rsync
> Before posting, read: http://www.catb.org/~esr/faqs/smart-
> questions.html
> 
> 
> 
> 




Karl <kop at meme.com>
Free Software:  "You don't pay back, you pay forward."
                 -- Robert A. Heinlein