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Race when attaching zfs datasets to jail?



Hi All,

Is it just me, or is there a race window between ezjail.sh invoking "zfs jail" from outside a jail and the jail running its /etc/rc.d/ zfs? In my case it manifests itself as follows: No ZFS file systems get mounted when the jail starts up but running "/etc/rc.d/zfs start" later on by hand gets all of them mounted. Of course, "zfs_enable=YES" is set in jail and the required sysctls are set, too, for otherwise it wouldn't have worked at all.

If my reading of the code is right, "zfs jail" isn't synchronised with the jail and a race can take place so "zfs jail" runs later than rc.d/ zfs. Unfortunately, this doesn't look like a mere bug in ezjail.sh fixable by tweaking some shell code. What is missing is a natural way to synchronise the execution of rc.d/zfs in a jail with the respective "zfs jail" in the host system. So the real issue can be in the FreeBSD kernel API and the most robust, if complicated, solution would be to attach ZFS datasets right in the jail(2) syscall so that there is no race window.

However, a possible workaround in ezjail for the time being can be to check the zfs_enable setting in the jail and run "zfs mount -a" on the jail's behalf after its datasets were attached.

Comments?

Thanks,
Yar