Removing the ability to run different zpools on top of a zvol is
a significant reduction in functionality of the entire system, and a
huge violation of the POLA.
At the very least, can you not add a sysctl that allows the
dangerous behavior (even if it defaults to off)? Myself
and certainly others rely on having being able to use a zpool
installed into a zvol for hosting bhyve virtual machines.
I've managed to deadlock the system when experimenting with this,
but for the normal course of operations, it works just fine.
-Kurt
On 1/19/16 12:00 PM, Alan Somers wrote:
Author: asomers
Date: Tue Jan 19 17:00:25 2016
New Revision: 294329
URL: https://svnweb.freebsd.org/changeset/base/294329
Log:
Disallow zvol-backed ZFS pools
Using zvols as backing devices for ZFS pools is fraught with panics and
deadlocks. For example, attempting to online a missing device in the
presence of a zvol can cause a panic when vdev_geom tastes the zvol. Better
to completely disable vdev_geom from ever opening a zvol. The solution
relies on setting a thread-local variable during vdev_geom_open, and
returning EOPNOTSUPP during zvol_open if that thread-local variable is set.
Remove the check for MUTEX_HELD(&zfsdev_state_lock) in zvol_open. Its intent
was to prevent a recursive mutex acquisition panic. However, the new check
for the thread-local variable also fixes that problem.
Also, fix a panic in vdev_geom_taste_orphan. For an unknown reason, this
function was set to panic. But it can occur that a device disappears during
tasting, and it causes no problems to ignore this departure.
Reviewed by: delphij
MFC after: 1 week
Relnotes: yes
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D4986
Modified:
head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/vdev_impl.h
head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c
head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_ioctl.c
head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zvol.c
[diff truncated]
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