Date: Thu, 4 Aug 2011 13:50:12 GMT From: Borja Marcos <borjam@sarenet.es> To: freebsd-fs@FreeBSD.org Subject: Re: kern/157728: [zfs] zfs (v28) incremental receive may leave behind temporary clones Message-ID: <201108041350.p74DoCTf071905@freefall.freebsd.org>
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The following reply was made to PR kern/157728; it has been noted by GNATS. From: Borja Marcos <borjam@sarenet.es> To: Martin Matuska <mm@FreeBSD.org> Cc: bug-followup@FreeBSD.org, Pawel Jakub Dawidek <pjd@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 :) >=20 > A workaround patch is attached that does not prefetch hidden datasets = in > 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 ;) Borja.
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