RFC: unionfs multiple mounts, cross mounts and recursive mounts
limits and manegement feature
daichi at freebsd.org
Thu Apr 21 06:06:07 UTC 2011
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.
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.
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