kern/157728: [zfs] zfs (v28) incremental receive may leave
behind temporary clones
borjam at sarenet.es
Thu Aug 4 13:50:12 UTC 2011
The following reply was made to PR kern/157728; it has been noted by GNATS.
From: Borja Marcos <borjam at sarenet.es>
To: Martin Matuska <mm at FreeBSD.org>
Cc: bug-followup at FreeBSD.org,
Pawel Jakub Dawidek <pjd at FreeBSD.org>
Subject: Re: kern/157728: [zfs] zfs (v28) incremental receive may leave behind temporary clones
Date: Thu, 4 Aug 2011 15:40:03 +0200
On Aug 4, 2011, at 2:33 PM, Martin Matuska wrote:
> That is not a solution, we want hidden datasets :)
> A workaround patch is attached that does not prefetch hidden datasets =
> zfs (btw. why should we do that at all).
> It doesn't cure the source of the problem but the symptoms - to
> reproduce the problem you have to run zfs list or get directly on the
> invisible temporary clone now.
Well, still there might be a subtle problem.
I mean, and sorry if it's a somewhat trivial question, but it-s the =
first time I actually read some ZFS internals code ;)
Does that prefetch *imply* a temporary lock being placed? I mean, in =
such a case usually you need an atomic fetch-and-lock
operation. I'm wondering if not prefetching them could be a problem, and =
instead it would be a better solution to keep prefetching them
but avoiding to display them, so that any side effects are preserved. =
Otherwise that might have some ugly interaction.
Of course my patch isn't a solution, I wanted a quick experiment to find =
out if the special treatment of the hidden datasets was the issue. But, =
really, the decision not to show a hidden dataset shouldn't be made at a =
such low level because of these interactions. The problem is, the patch =
might work but introduce harder to reproduce issues?
Maybe Pawel can help us, I guess he's much more familiar than us with =
the guts of ZFS ;)
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