If zp->z_unlinked is set, we're working with a znode that has been
marked for deletion. If that's the case, we can skip the "goto again"
loop and return ENOENT, as the znode should not be discovered.
Reviewed-by: Richard Yao <ryao@gentoo.org>
Reviewed-by: Matt Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Heitor Alves de Siqueira <halves@canonical.com>
Closes#9583
blkg_tryget() as shipped in EL8 kernels does not seem to handle NULL
@blkg as input; this is different from its mainline counterpart where
NULL is accepted. To prevent dereferencing a NULL pointer when dealing
with block devices which do not set a root_blkg on the request queue
perform the NULL check in vdev_bio_associate_blkg().
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Kjeld Schouten <kjeld@schouten-lebbing.nl>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes#9546Closes#9577
Increase the minimum supported kernel version from 2.6.32 to 3.10.
This removes support for the following Linux enterprise distributions.
Distribution | Kernel | End of Life
---------------- | ------ | -------------
Ubuntu 12.04 LTS | 3.2 | Apr 28, 2017
SLES 11 | 3.0 | Mar 32, 2019
RHEL / CentOS 6 | 2.6.32 | Nov 30, 2020
The following changes were made as part of removing support.
* Updated `configure` to enforce a minimum kernel version as
specified in the META file (Linux-Minimum: 3.10).
configure: error:
*** Cannot build against kernel version 2.6.32.
*** The minimum supported kernel version is 3.10.
* Removed all `configure` kABI checks and matching C code for
interfaces which solely predate the Linux 3.10 kernel.
* Updated all `configure` kABI checks to fail when an interface is
missing which was in the 3.10 kernel up to the latest 5.1 kernel.
Removed the HAVE_* preprocessor defines for these checks and
updated the code to unconditionally use the verified interface.
* Inverted the detection logic in several kABI checks to match
the new interface as it appears in 3.10 and newer and not the
legacy interface.
* Consolidated the following checks in to individual files. Due
the large number of changes in the checks it made sense to handle
this now. It would be desirable to group other related checks in
the same fashion, but this as left as future work.
- config/kernel-blkdev.m4 - Block device kABI checks
- config/kernel-blk-queue.m4 - Block queue kABI checks
- config/kernel-bio.m4 - Bio interface kABI checks
* Removed the kABI checks for sops->nr_cached_objects() and
sops->free_cached_objects(). These interfaces are currently unused.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#9566
This patch removes the need for zpl_revalidate altogether.
There were 3 main reasons why we used d_revalidate:
1. periodic automounted snapshots umount deferral
2. negative dentries created before snapshot rollback
3. stale inodes referenced by dentry cache after snapshot rollback
Periodic snapshots deferral solution introduces zfs_exit_fs function,
which is called as a part of ZFS_EXIT(zfsvfs_t) macro.
Negative dentries and stale inodes are solved by flushing the dcache
for the particular dataset on zfs_resume_fs call.
This patch also removes now unused HAVE_S_D_OP configure test.
Reviewed-by: Aleksa Sarai <cyphar@cyphar.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Pavel Snajdr <snajpa@snajpa.net>
Closes#8774Closes#9549
Some of the znode fields are different and functions
consuming an inode don't exist on FreeBSD.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9536
This change modifies some of the infrastructure for enabling the use of
the DTRACE_PROBE* macros, such that we can use tehm in the "spl" module.
Currently, when the DTRACE_PROBE* macros are used, they get expanded to
create new functions, and these dynamically generated functions become
part of the "zfs" module.
Since the "spl" module does not depend on the "zfs" module, the use of
DTRACE_PROBE* in the "spl" module would result in undefined symbols
being used in the "spl" module. Specifically, DTRACE_PROBE* would turn
into a function call, and the function being called would be a symbol
only contained in the "zfs" module; which results in a linker and/or
runtime error.
Thus, this change adds the necessary logic to the "spl" module, to
mirror the tracing functionality available to the "zfs" module. After
this change, we'll have a "trace_zfs.h" header file which defines the
probes available only to the "zfs" module, and a "trace_spl.h" header
file which defines the probes available only to the "spl" module.
Reviewed by: Brad Lewis <brad.lewis@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Prakash Surya <prakash.surya@delphix.com>
Closes#9525
MODULE_VERSION is already defined on FreeBSD. Wrap all of the
used MODULE_* macros for the sake of consistency and portability.
Add a user space noop version to reduce the need for _KERNEL ifdefs.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9542
A struct rangelock already exists on FreeBSD. Add a zfs_ prefix as
per our convention to prevent any conflict with existing symbols.
This change is a follow up to 2cc479d0.
Reviewed-by: Matt Ahrens <matt@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9534
The FreeBSD implementation can fail, allow this function to
fail and add the required error handling for Linux.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9541
Move these Linux module parameter get/set helpers in to
platform specific code.
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9457
This change leverage module_param_call() to run arc_tuning_update()
immediately after the ARC tunable has been updated as suggested in
cffa8372 code review.
A simple test case is added to the ZFS Test Suite to prevent future
regressions in functionality.
Reviewed-by: Matt Macy <mmacy@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes#9487Closes#9489
This logic is not platform dependent and should reside in the
common code.
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9505
It's mostly a noop on ZoL and it conflicts with platforms that
support dtrace. Remove this header to resolve the conflict.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9497
Contrary to initial testing we cannot rely on these kernels to
invalidate the per-cpu FPU state and restore the FPU registers.
Nor can we guarantee that the kernel won't modify the FPU state
which we saved in the task struck.
Therefore, the kfpu_begin() and kfpu_end() functions have been
updated to save and restore the FPU state using our own dedicated
per-cpu FPU state variables.
This has the additional advantage of allowing us to use the FPU
again in user threads. So we remove the code which was added to
use task queues to ensure some functions ran in kernel threads.
Reviewed-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #9346Closes#9403
Factor Linux specific memory pressure handling out of ARC. Each
platform will have different available interfaces for managing memory
pressure.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9472
Only pass the file descriptor to make zfsdev_get_miror() portable.
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9466
Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9465
FreeBSD has a very different implementation.
Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9442
FreeBSD has its own implementation as do other platforms.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9439
Temporary property handling at the VFS layer requires
platform specific code.
Reviewed-by: Sean Eric Fagan <sef@ixsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9401
In the FreeBSD kernel the strdup signature is:
```
char *strdup(const char *__restrict, struct malloc_type *);
```
It's unfortunate that the developers have chosen to change
the signature of libc functions - but it's what I have to
deal with.
Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9433
This patch implements a new tree structure for ZFS, and uses it to
store range trees more efficiently.
The new structure is approximately a B-tree, though there are some
small differences from the usual characterizations. The tree has core
nodes and leaf nodes; each contain data elements, which the elements
in the core nodes acting as separators between its children. The
difference between core and leaf nodes is that the core nodes have an
array of children, while leaf nodes don't. Every node in the tree may
be only partially full; in most cases, they are all at least 50% full
(in terms of element count) except for the root node, which can be
less full. Underfull nodes will steal from their neighbors or merge to
remain full enough, while overfull nodes will split in two. The data
elements are contained in tree-controlled buffers; they are copied
into these on insertion, and overwritten on deletion. This means that
the elements are not independently allocated, which reduces overhead,
but also means they can't be shared between trees (and also that
pointers to them are only valid until a side-effectful tree operation
occurs). The overhead varies based on how dense the tree is, but is
usually on the order of about 50% of the element size; the per-node
overheads are very small, and so don't make a significant difference.
The trees can accept arbitrary records; they accept a size and a
comparator to allow them to be used for a variety of purposes.
The new trees replace the AVL trees used in the range trees today.
Currently, the range_seg_t structure contains three 8 byte integers
of payload and two 24 byte avl_tree_node_ts to handle its storage in
both an offset-sorted tree and a size-sorted tree (total size: 64
bytes). In the new model, the range seg structures are usually two 4
byte integers, but a separate one needs to exist for the size-sorted
and offset-sorted tree. Between the raw size, the 50% overhead, and
the double storage, the new btrees are expected to use 8*1.5*2 = 24
bytes per record, or 33.3% as much memory as the AVL trees (this is
for the purposes of storing metaslab range trees; for other purposes,
like scrubs, they use ~50% as much memory).
We reduced the size of the payload in the range segments by teaching
range trees about starting offsets and shifts; since metaslabs have a
fixed starting offset, and they all operate in terms of disk sectors,
we can store the ranges using 4-byte integers as long as the size of
the metaslab divided by the sector size is less than 2^32. For 512-byte
sectors, this is a 2^41 (or 2TB) metaslab, which with the default
settings corresponds to a 256PB disk. 4k sector disks can handle
metaslabs up to 2^46 bytes, or 2^63 byte disks. Since we do not
anticipate disks of this size in the near future, there should be
almost no cases where metaslabs need 64-byte integers to store their
ranges. We do still have the capability to store 64-byte integer ranges
to account for cases where we are storing per-vdev (or per-dnode) trees,
which could reasonably go above the limits discussed. We also do not
store fill information in the compact version of the node, since it
is only used for sorted scrub.
We also optimized the metaslab loading process in various other ways
to offset some inefficiencies in the btree model. While individual
operations (find, insert, remove_from) are faster for the btree than
they are for the avl tree, remove usually requires a find operation,
while in the AVL tree model the element itself suffices. Some clever
changes actually caused an overall speedup in metaslab loading; we use
approximately 40% less cpu to load metaslabs in our tests on Illumos.
Another memory and performance optimization was achieved by changing
what is stored in the size-sorted trees. When a disk is heavily
fragmented, the df algorithm used by default in ZFS will almost always
find a number of small regions in its initial cursor-based search; it
will usually only fall back to the size-sorted tree to find larger
regions. If we increase the size of the cursor-based search slightly,
and don't store segments that are smaller than a tunable size floor
in the size-sorted tree, we can further cut memory usage down to
below 20% of what the AVL trees store. This also results in further
reductions in CPU time spent loading metaslabs.
The 16KiB size floor was chosen because it results in substantial memory
usage reduction while not usually resulting in situations where we can't
find an appropriate chunk with the cursor and are forced to use an
oversized chunk from the size-sorted tree. In addition, even if we do
have to use an oversized chunk from the size-sorted tree, the chunk
would be too small to use for ZIL allocations, so it isn't as big of a
loss as it might otherwise be. And often, more small allocations will
follow the initial one, and the cursor search will now find the
remainder of the chunk we didn't use all of and use it for subsequent
allocations. Practical testing has shown little or no change in
fragmentation as a result of this change.
If the size-sorted tree becomes empty while the offset sorted one still
has entries, it will load all the entries from the offset sorted tree
and disregard the size floor until it is unloaded again. This operation
occurs rarely with the default setting, only on incredibly thoroughly
fragmented pools.
There are some other small changes to zdb to teach it to handle btrees,
but nothing major.
Reviewed-by: George Wilson <gwilson@delphix.com>
Reviewed-by: Matt Ahrens <matt@delphix.com>
Reviewed by: Sebastien Roy seb@delphix.com
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Paul Dagnelie <pcd@delphix.com>
Closes#9181
Commit 093bb64 resolved an automount failures for chroot'd processes
but inadvertently broke automounting for root filesystems where the
vfs_mntpoint is NULL. Resolve the issue by checking for NULL in order
to generate the correct path.
Reviewed-by: Tom Caputi <tcaputi@datto.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#9381Closes#9384
A rangelock KPI already exists on FreeBSD. Add a zfs_ prefix as
per our convention to prevent any conflict with existing symbols.
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9402
We've seen cases where after creating a ZVOL, the ZVOL device node in
"/dev" isn't generated after 20 seconds of waiting, which is the point
at which our applications gives up on waiting and reports an error.
The workload when this occurs is to "refresh" 400+ ZVOLs roughly at the
same time, based on a policy set by the user. This refresh operation
will destroy the ZVOL, and re-create it based on a snapshot.
When this occurs, we see many hundreds of entries on the "z_zvol" taskq
(based on inspection of the /proc/spl/taskq-all file). Many of the
entries on the taskq end up in the "zvol_remove_minors_impl" function,
and I've measured the latency of that function:
Function = zvol_remove_minors_impl
msecs : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 1 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 1 | |
128 -> 255 : 45 |****************************************|
256 -> 511 : 5 |**** |
That data is from a 10 second sample, using the BCC "funclatency" tool.
As we can see, in this 10 second sample, most calls took 128ms at a
minimum. Thus, some basic math tells us that in any 20 second interval,
we could only process at most about 150 removals, which is much less
than the 400+ that'll occur based on the workload.
As a result of this, and since all ZVOL minor operations will go through
the single threaded "z_zvol" taskq, the latency for creating a single
ZVOL device can be unreasonably large due to other ZVOL activity on the
system. In our case, it's large enough to cause the application to
generate an error and fail the operation.
When profiling the "zvol_remove_minors_impl" function, I saw that most
of the time in the function was spent off-cpu, blocked in the function
"taskq_wait_outstanding". How this works, is "zvol_remove_minors_impl"
will dispatch calls to "zvol_free" using the "system_taskq", and then
the "taskq_wait_outstanding" function is used to wait for all of those
dispatched calls to occur before "zvol_remove_minors_impl" will return.
As far as I can tell, "zvol_remove_minors_impl" doesn't necessarily have
to wait for all calls to "zvol_free" to occur before it returns. Thus,
this change removes the call to "taskq_wait_oustanding", so that calls
to "zvol_free" don't affect the latency of "zvol_remove_minors_impl".
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: John Gallagher <john.gallagher@delphix.com>
Signed-off-by: Prakash Surya <prakash.surya@delphix.com>
Closes#9380
Refactor the zfs ioctls in to platform dependent and independent bits.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Sean Eric Fagan <sef@ixsystems.com>
Signed-off-by: Matthew Macy <mmacy@FreeBSD.org>
Signed-off-by: Ryan Moeller <ryan@ixsystems.com>
Closes#9301
Originally the zfs_vdev_elevator module option was added as a
convenience so the requested elevator would be automatically set
on the underlying block devices. At the time this was simple
because the kernel provided an API function which did exactly this.
This API was then removed in the Linux 4.12 kernel which prompted
us to add compatibly code to set the elevator via a usermodehelper.
While well intentioned this introduced a bug which could cause a
system hang, that issue was subsequently fixed by commit 2a0d4188.
In order to avoid future bugs in this area, and to simplify the code,
this functionality is being deprecated. A console warning has been
added to notify any existing consumers and the documentation updated
accordingly. This option will remain for the lifetime of the 0.8.x
series for compatibility but if planned to be phased out of master.
Reviewed-by: Richard Laager <rlaager@wiktel.com>
Reviewed-by: loli10K <ezomori.nozomu@gmail.com>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #8664Closes#9317
Refactor the zvol in to platform dependent and independent bits.
Reviewed-by: Allan Jude <allanjude@freebsd.org>
Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9295
Originally the zfs_vdev_elevator module option was added as a
convenience so the requested elevator would be automatically set
on the underlying block devices. At the time this was simple
because the kernel provided an API function which did exactly this.
This API was then removed in the Linux 4.12 kernel which prompted
us to add compatibly code to set the elevator via a usermodehelper.
Unfortunately changing the evelator via usermodehelper requires reading
some userland binaries, most notably modprobe(8) or sh(1), from a zfs
dataset on systems with root-on-zfs. This can deadlock the system if
used during the following call path because it may need, if the data
is not already cached in the ARC, reading directly from disk while
holding the spa config lock as a writer:
zfs_ioc_pool_scan()
-> spa_scan()
-> spa_scan()
-> vdev_reopen()
-> vdev_elevator_switch()
-> call_usermodehelper()
While the usermodehelper waits sh(1), modprobe(8) is blocked in the
ZIO pipeline trying to read from disk:
INFO: task modprobe:2650 blocked for more than 10 seconds.
Tainted: P OE 5.2.14
modprobe D 0 2650 206 0x00000000
Call Trace:
? __schedule+0x244/0x5f0
schedule+0x2f/0xa0
cv_wait_common+0x156/0x290 [spl]
? do_wait_intr_irq+0xb0/0xb0
spa_config_enter+0x13b/0x1e0 [zfs]
zio_vdev_io_start+0x51d/0x590 [zfs]
? tsd_get_by_thread+0x3b/0x80 [spl]
zio_nowait+0x142/0x2f0 [zfs]
arc_read+0xb2d/0x19d0 [zfs]
...
zpl_iter_read+0xfa/0x170 [zfs]
new_sync_read+0x124/0x1b0
vfs_read+0x91/0x140
ksys_read+0x59/0xd0
do_syscall_64+0x4f/0x130
entry_SYSCALL_64_after_hwframe+0x44/0xa9
This commit changes how we use the usermodehelper functionality from
synchronous (UMH_WAIT_PROC) to asynchronous (UMH_NO_WAIT) which prevents
scrubs, and other vdev_elevator_switch() consumers, from triggering the
aforementioned issue.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Issue #8664Closes#9321
1. Fix issue: Kernel BUG with QAT during decompression #9276.
Now it is uninterruptible for a specific given QAT request,
but Ctrl-C interrupt still works in user-space process.
2. Copy the digest result to the buffer only when doing encryption,
and vise-versa for decryption.
Reviewed-by: Tom Caputi <tcaputi@datto.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chengfei Zhu <chengfeix.zhu@intel.com>
Closes#9276Closes#9303
objnode is OS agnostic and used only by dmu_redact.c.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9315
Move Linux specific tracing headers and source to platform directories
and update the build system.
Reviewed-by: Allan Jude <allanjude@freebsd.org>
Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Reviewed by: Brad Lewis <brad.lewis@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9290
When adding the SIMD compatibility code in e5db313 the decryption of a
dataset wrapping key was left in a user thread context. This was done
intentionally since it's a relatively infrequent operation. However,
this also meant that the encryption context templates were initialized
using the generic operations. Therefore, subsequent encryption and
decryption operations would use the generic implementation even when
executed by an I/O pipeline thread.
Resolve the issue by initializing the context templates in an I/O
pipeline thread. And by updating zio_do_crypt_uio() to dispatch any
encryption operations to a pipeline thread when called from the user
context. For example, when performing a read from the ARC.
Tested-by: Attila Fülöp <attila@fueloep.org>
Reviewed-by: Tom Caputi <tcaputi@datto.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#9215Closes#9296
Move platform specific Linux source under module/os/linux/
and update the build system accordingly. Additional code
restructuring will follow to make the common code fully
portable.
Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matthew Macy <mmacy@FreeBSD.org>
Closes#9206
