Date: Thu, 21 Apr 2011 14:49:47 +0900 From: Daichi GOTO <daichi@freebsd.org> To: freebsd-current@freebsd.org, freebsd-fs@freebsd.org Subject: RFC: unionfs multiple mounts, cross mounts and recursive mounts limits and manegement feature Message-ID: <20110421144947.b887081e.daichi@freebsd.org>
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Hi unionfs lovers, It is possible to mount unionfs multiple times more than once at a mount point. However, exceeding multiple mounts could consume kernel stack over its limits and lead a system panic easily. Some users reported that they got a system panic by multiple unionfs mounts. So I make a preproduction prototype to check multiple mounts, cross mounts, recursive mounts and the combination of those of unionfs and prevent that situation. http://people.freebsd.org/~daichi/unionfs/experiments/unionfs-cross-mount3.diff It is adjustable with sysctl value 'vfs.unionfs.recursive_limit' as multiple mounts limits. The default value is 1 and it means two-layered ok. Max value of 'vfs.unionfs.recursive_limit' is 8, it is heuristic value. I couldn't get a system panic unless 'vfs.unionfs.recursive_limit' is over 8. Test reports, suggestions and new patches are always welcome. I'm considering to get merged into current if there are no issues and problems. -- Daichi GOTO
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