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Date: Tue, 01 May 2012 21:29:48 -0500
From: Bryan Drewery <bryan@shatow.net>
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Cc: vermaden <vermaden@interia.pl>
Subject: ZFS canmount=on (from noauto) on mounted datasets
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What am I missing here? On 9-RELEASE. I am unable to change 'canmount'
from 'noauto' to 'on', on an already-auto-mounted dataset.
# mount|grep "/var/log"
zroot/ROOT/freebsd90/var/log on /var/log (zfs, local, noatime, noexec,
nosuid, nfsv4acls)
# zfs get -H -o value mounted zroot/ROOT/freebsd90/var/log
yes
# zfs get -H -o value canmount zroot/ROOT/freebsd90/var/log
noauto
# zfs set canmount=on zroot/ROOT/freebsd90/var/log
cannot unmount '/var/log': Device busy
^^^^
I don't see any reference in zfs(1M) to 'canmount' causing automatically
causing a [re]mount. This is understandable for 'mountpoint' of course.
It seems zfs_prop_set() in libzfs_changelist is doing this by calling
changelist_prefix(), as long as not using 'noauto', which does a remount.
The comments for changelist_prop() indicate it's for changing
'mountpoint', which makes sense. Is this being incorrectly called in
zfs_prop_set() for 'canmount=on/off'?
The HEAD code looks to be prone to this as well in zfs_prop_set().
Code in question:
/*
* If the dataset's canmount property is being set to noauto,
* then we want to prevent unmounting & remounting it.
*/
do_prefix = !((prop == ZFS_PROP_CANMOUNT) &&
(zprop_string_to_index(prop, propval, &idx,
ZFS_TYPE_DATASET) == 0) && (idx == ZFS_CANMOUNT_NOAUTO));
if (do_prefix && (ret = changelist_prefix(cl)) != 0)
goto error;
Regards,
Bryan Drewery
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