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Move commod code to destroy orphan VG into free_orphan_vg() function.
Use orphan vgmem for creation of PV lists.
Remove some free_pv_fid() calls (FIXME: check all of them)
FIXME: Check whether we could merge release_vg back again for all VGs.
label_exit() is called destroy_toolcontext() and we are now
using standard dm_list function for destroy, we have to make sure
dm_list gets initialized properly.
As atoi may return negative value - test for both limits.
Test log_args for limits before calling alloca().
Code from dmeventd mirror plugin should probably share same code as
we have in mirrored.c.
Since the function dev_close() has code path, which really could close
file (for unlocked vg) and destroy dev handler, stay on safe side and move
the close few lines later, even our current use case shouldn't trigger
such scenario.
Count number of error and existing areas and if there is no existing area
for the LV avoid its activation.
Always disable partial activatio for thin volumes.
For mirrors currently put in hack to let it pass with a special name
since current mirror code needs to activate such LV during some operations.
For reading % of mapped size of thin volume use as origin for
old style snapshot '-real' device needs to be queried.
Fix log_error report given for lvs -a in this case.
Before removing thin pool LV always make sure, stacked message
for previous run are cleared - but allow to remove any
device that should have been created
(i.e. creation of snapshot failed - so the message for snapshot creation
may be replaced with delete message within unfinished transaction).
Also commit messages after lv remove - so free space is released in pool.
Extend the usage of origin_only flag to allow resume of thin pool LV
(when it's active) to pass only the messages.
origin_only flag will skip detection of already resumed tree for thin_pool,
so we do not need to suspend the tree and we just send messages.
Pass in the origin_only flag also for thin volumes - but curently the flag
is not used to its best.
FIXME: achieve the state where only thin volume snapshot origin is
suspended without its childrens - let's explore whether this may
happen automatically inside libdm (might be generic for other targets).
So the code would not need to annotate the node for this.
Extend lv_activate_opts with bool flag to know for which purpose
dtree is created - and add message only for activation tree
(since that's the only place that may send them).
Extend validation check for thin snapshot creation and test whether
active snapshot origin is suspended before its snapshot is created
(useful in recover scenarios) - in this case also detect, whether
transaction has been already completed and avoid such suspend check
failure in that case.
Add pool_has_message and use it in attach_pool_message.
Also update header to make more obvious which segment type is
expected as parameter.
Rename 'read_only' to 'no_update' (no auto update transaction_id)
to better fit how it's used.
Fix problem when there was only one stacked message replaced with delete
message that caused unwanted transaction_id increase.
Failure to do so results in "Performing unsafe table load while X device(s) are
known to be suspended" errors. While fixing the problem in this way works and
is consistent with the way the mirror segment type does it, it would be nice
to find a solution that uses the generic suspend/resume calls.
Also included in this check-in are additions to the test suite that perform
conversions on RAID LVs under a snapshot. These tests are disabled for the
time being due to a kernel bug that is yet to be tracked down.
Similar to the "mirror" segment type's log device, _add_dev_to_dtree should
be called and not _add_lv_to_dtree when adding metadata sub-LVs to the deptree.
Since _add_lv_to_dtree was being called, 'origin_only' could be set if a
snapshot sits on top of the RAID device. This would cause the actual device
that needed to be added to be skipped in favor of the non-existant device,
"<foo>-real".
Reformat name and path how the LV is represented with lvm1 compatible option,
to switch to the old way - which had number of problem - i.e. many links
do not exist - since for private devices we are not creating them.
Add more info about thin pools and volumes.
Since striped name function knows when to report 'linear' instead of
'stripe' type name - drop it from this place.
This fixes problem when reporting segtype e.g. for thin-pool which
is also using area_count=1 to store thin data device reference.
It also returns properly strduped memory instead of badly casted const char*.
This patch to the suspend code - like the similar change for resume -
queries the lock mode of a cluster volume and records whether it is active
exclusively. This is necessary for suspend due to the possibility of
preloading targets. Failure to check to exclusivity causes the cluster target
of an exclusively activated mirror to be used when converting - rather than
the single machine target.
Since snapshot needs to suspend origin - it might lead to pool userspace
deadlock (as the pool will wait for new space in case it would be overfilled,
but dmeventd would not be able to resize it, as the lvcreate operation would
have kept the VG lock.)
To minimize the risk of such scenario - we prevent to create new snapshot
in case we are over the threshold - but beware, there is still small timewindow,
so keep threshold at some reasonable level!
New field Data% is able to display info about
thin_pool, thin, snapshot and has generic meaning here.
Simple Time/Host field are here to display host and time creation.
Basic support to keep info when the LV was created.
Host and time is stored into LV mda section.
FIXME: Current version doesn't support configurable string via lvm.conf
and used fixed version strftime "%Y-%m-%d %T %z".
This value returns percentage of 'mapped' size compared with total LV size.
(Without passed seg pointer it return highest mapped size - but it's
not used yet.)
LVM- prefix.
Try harder not to leave stray empty devices around (locally or remotely) when
reverting changes after failures while there are inactive tables.
Since the !(dev->flags & DEV_REGULAR) code path just called
dev_name_confirmed() which has just called 'stat()' inside,
remove duplicate second stat() call here.
When both path have identical prefix i.e. /dev/disk/by-id
skip 2 x lstat() for /dev /dev/disk /dev/disk/by-id
and directly lstat() only different part of the path.
Reduces amount of lstat calls on system with lots of devices.
The RAID plug-in for dmeventd now calls 'lvconvert --repair' to address failures
of devices in a RAID logical volume. The action taken can be either to "warn"
or "allocate" a new device from any spares that may be available in the
volume group. The action is designated by setting 'raid_fault_policy' in
lvm.conf - the default being "warn".
Also, don't allow a splitmirror operation on a RAID LV that is already tracking
a split, unless the operation is to stop the tracking and complete the split.
Example:
~> lvconvert --splitmirrors 1 --trackchanges vg/lv /dev/sdc1
# Now tracking changes - image can be merged back or split-off for good
~> lvconvert --splitmirrors 1 -n new_name vg/lv /dev/sdc1
# ^ Completes split ^
If a split is performed on a RAID that is tracking an already split image and
PVs are provided, we must ensure that
1) the already split LV is represented in the PVs
2) we are careful to split only the tracked image
RAID is not like traditional LVM mirroring. LVM mirroring required failed
devices to be removed or the logical volume would simply hang. RAID arrays can
keep on running with failed devices. In fact, for RAID types other than RAID1,
removing a device would mean substituting an error target or converting to a
lower level RAID (e.g. RAID6 -> RAID5, or RAID4/5 to RAID0). Therefore, rather
than removing a failed device unconditionally and potentially allocating a
replacement, RAID allows the user to "replace" a device with a new one. This
approach is a 1-step solution vs the current 2-step solution.
example> lvconvert --replace <dev_to_remove> vg/lv [possible_replacement_PVs]
'--replace' can be specified more than once.
example> lvconvert --replace /dev/sdb1 --replace /dev/sdc1 vg/lv
LVM metadata knows only of striped segments - not linear ones.
The activation code detects segments with a single stripe and switches
them to use the linear target.
If the new lvm.conf setting is set to 0 (e.g. in a test script), this
'optimisation' is turned off.
Remove FIXMES - there should not be any pool free call since
the memory pool is from device manager, and pool is detroyed
after the operation, so doing extra free here would not help here.
However lv_has_target_type() is using cmd mempool so here the extra
call for dm_pool_free makes sence.
"result_independent_of_operands: ((dev->dev & 0xfff00UL) >> 8) ==
18446744073709551615UL /* -1 */ is always false regardless of the values
of its operands (logical operand of if)."
'dev->dev' is set in dev-cache.c _insert() and it's not expectable
st_rdev would have '-1'
This code has been introduced with drbd support commit and code never
worked - so eliminated.
Use static buffer instead of stack allocated buffer.
This reduces stack size usage of lvm tool and the
change is very simple.
Since the whole library is not thread safe - it should not
add any new problems - and if there will be some conversion
it's easy to convert this to use some preallocated buffer.
For write we do not need to hold memory locked.
This relaxes many conditions and avoid problems when allocating
a lot of memory for writting metadata buffers.
(In case of huge MDA size this would lead to mismatch between
locked and unlocked memory region size).
Add also internal check we are not writing in critical section.
Removal of an inactive origin removes also all related snapshots.
When we now support 'old' external snapshots with thin volumes,
removal of pool will not only drop all thin volumes, but as
a consequence also all snapshots - which might be seen a bit
unexpected for the user - so add a query to confirm such action.
lvremove -f will skip the prompt.
Update region_size only for mirror and raid targets.
This fixes warning messages when vg is using small
extent size like 1KiB and no mirror/raid is created,
but the user still got the message:
$> vgcreate -s 1K vg <pvs>
$> lvcreate -L10K vg
Using reduced mirror region size of 4 sectors
Since we support snapshots of thin volumes, we could have more layers,
so we have to check whether tpool layer is going to be inserted.
As the _add_segment_to_dtree() is the only place that adds tpool
segment, we may just check pointer (no strcmp for layer).
Switch to use seg_is_ function instead of lv_is_.
When a PV label write is deferred to a vg_write call (as introduced by a patch
in 2.02.86), the PV is flagged with the internal UNLABELLED_PV flag. However,
when calling vg_archive before vg_write, we still have the PV labelled with the
UNLABELLED_PV flag which was not recognised as a proper flag while exporting
VG metadata:
# vgcreate vg /dev/sda
No physical volume label read from /dev/sda
Metadata inconsistency: Not all flags successfully exported.
Metadata inconsistency: Not all flags successfully exported.
Writing physical volume data to disk "/dev/sda"
Physical volume "/dev/sda" successfully created
Volume group "vg" successfully created
Remove DM_THIN_ERROR_DEVICE_ID from API.
Remove API warning.
Drop code that was using DM_THIN_ERROR_DEVICE_ID (already commented)
Remove debug message which slipped in through some previous commit.
Add filter which tries to check if scanned device is part
of active multipath.
Firstly, only SCSI major number devices are handled in filter.
Then it checks if device has exactly one holder (in sysfs) and
if it is device-mapper device and DM-UUID is prefixed by "MPATH-".
If so, this device is filtered out.
The whole filter can be switched off by setting
mpath_component_detection in lvm.conf.
https://bugzilla.redhat.com/show_bug.cgi?id=597010
Signed-off-by: Milan Broz <mbroz@redhat.com>
If the extent_size is smaller then the chunk_size we may try
to find better aligment (wasting less space).
i.e. using 4KB extent_size and 64KB chunk size will
lead to creation of 64KB aligned thin volume.
Support allocation of metadata from the same PV, if the VG
is build only from one PV.
As thinp is not mirror - we do not require 2 PVs
for basic thin usage as user is losing only perfomance.
Replace detach_pool_messages with update_pool_lv.
Move creation code from to 'if' condition into 1.
Ensure creation has finished all previous message operations.
Let's put the overlay device over real thin pool device.
So we can get the proper locking on cluster.
Overwise the pool LV would be activate once implicitely
and in other case explicitely, confusing locking mechanism.
This patch make the activation of pool LV independent on
activation of thin LV since they will both implicitely use
real -thin pool device.
All thins are created with the next activation and VG is updated
without messages. Only some basic commands works.
(i.e. lvcreate -an -V10 -T mvg/pool)
There can be some combination to confuse this system.
This functionality for snapshots is going to be interesting.
If something fails during creation of thin LV remove such LV
and deactivate in case it's been already tried to activate
(i.e. thin kernel driver fails for some reason.)
To ensure we properly handle LV cluster locking - explicitely do
not allow to change the availability of the thin pool that is in use
for some thin LV.
As soon as the thin volume is created the only way to activate pool
is via implicit dependency.
Ignore thinpool open count for lv/vgchange operations.
Before adding a new virtual segment to LV, check first whether
the last segment isn't already of the same type. In this case
extend last segment instead of creating the new one.
Thin volumes should have always only 1 virtual segment, but it
helps also to virtual snapshot or error segtype..
Git commit ID 0864378250 was meant to disallow
'mirrored' logs for cluster mirrors. However, when add_mirror_log is used
to create the log (as is now the case when using 'lvcreate' or converting only
the log) the check is bypassed.
This patch adds the check to add_mirror_log.
pvck prints 'extra' character from the label since there is no '\0'
after the struct label entry and just uint64_t follows directly.
So avoid it by limiting 8 chars to be printed.
https://www.redhat.com/archives/lvm-devel/2011-January/msg00109.html
Signed-off-by: Paul Bolle <pebolle tiscali nl>
Since thin is not able to use _lv_insert_empty_sublvs,
remove its appearence from this function.
Start to use extend_pool() function for desired functionality
and modify lv_extend() for this.
Code in _lv_insert_empty_sublvs was not able to provide proper
initialization order for thin pool LV.
New function extend_pool() first adds metadata segment to pool LV which
is still visible. Such LV is activate and cleared.
Then new meta LV is created and metadata segments are moved there.
Now the preallocated pool data segment is attached to the pool LV
and layer _tpool is created. Finaly segment is marked as thin_pool.
This function could be useful for other _manip source files.
Use dm_list manipulation function for provided functionality,
which make the code more readable and avoid touching list
internal details here.
This was the intended behaviour, as described in the lvchange man page, so you
have complete control through volume_list in lvm.conf, but the code seems to
have been treating -ae as local-only for a very long time.
Couple FIXMEs put into the code for parts of the code which may be
improved later, since we might be able to add 'lazy' device creation later.
For now require exclusive activation.
lvm part of messaging.
Each message is now stored it's own thin pool section:
message1 {
create = lv
}
Messages are queued to thin pool dm target when this target
is going to be resumed or used through some dependency.
Currently 'delete' message are purely queued and processed
with next thin pool resume operation (i.e. create_thin).
WARNING - thin provisioning support is developmental code.
When verify_udev_operations was disable, code for stacking fs operation for
lvm links was completely disable - but this code was also used for collecting
information, that a new node is being created.
Add a new flag which is set when a creation of lv symlinks is requested which
should restore old behaviour of lv_info function, that has called fs_sync()
before quere for open count on device.
Go with just 64KiB for stack.
Closer inspection should be made, whether we actually need to play with
settings at all.
Since default stack size is 8MB and gets mapped via page locking thus,
it seems there is no big help with preallocation of stack to some value.
Properly detect if the filters were refreshed properly.
(May needs few more fixes ??)
Filter refresh may fail because it may be out of free file descriptors
when clvmd gets overloaded.
Using log_warn to report missing symlinks as warning, since the command
itself returns as successful, we should not produce log_error().
log_warn is better fit here.
Cosmetic, since r is already 0 for the error path, no need to assign it there,
and r is assigned to 1 after switch command.
Also makes the code more readable.
Example:
~> lvconvert --type raid1 vg/mirror_lv
Steps to convert "mirror" to "raid1"
1) Allocate a RAID metadata LV for each mirror image from the same PVs
on which they are located.
2) Clear the metadata LVs. This involves writing LVM metadata, so we don't
change any aspects of the mirror LV before this so that the user can easily
remove LVs from the failed convert attempt while retaining the original
mirror.
3) Remove the mirror log, if it exists.
4) Add metadata LVs to mirror LV
5) Rename mirror sub-lvs (s/mimage/rimage/)
6) Change flags and segtype from mirror to raid1
Example:
~> lvconvert --type raid1 -m 1 vg/lv
The following steps are performed to convert linear to RAID1:
1) Allocate a metadata device from the same PV as the linear device
to provide the metadata/data LV pair required for all RAID components.
2) Allocate the required number of metadata/data LV pairs for the
remaining additional images.
3) Clear the metadata LVs. This performs a LVM metadata update.
4) Create the top-level RAID LV and add the component devices.
We want to make any failure easy to unwind. This is why we don't create the
top-level LV and add the components until the last step. Should anything
happen before that, the user could simply remove the unnecessary images. Also,
we want to ensure that the metadata LVs are cleared before forming the array to
prevent stale information from polluting the new array.
A new macro 'seg_is_linear' was added to allow us to distinguish linear LVs
from striped LVs.
This patch allows a mirror to be extended without an initial resync of the
extended portion. It compliments the existing '--nosync' option to lvcreate.
This action can be done implicitly if the mirror was created with the '--nosync'
option, or explicitly if the '--nosync' option is used when extending the device.
Here are the operational criteria:
1) A mirror created with '--nosync' should extend with 'nosync' implicitly
[EXAMPLE]# lvs vg; lvextend -L +5G vg/lv ; lvs vg
LV VG Attr LSize Pool Origin Snap% Move Log Copy% Convert
lv vg Mwi-a-m- 5.00g lv_mlog 100.00
Extending 2 mirror images.
Extending logical volume lv to 10.00 GiB
Logical volume lv successfully resized
LV VG Attr LSize Pool Origin Snap% Move Log Copy% Convert
lv vg Mwi-a-m- 10.00g lv_mlog 100.00
2) The 'M' attribute ('M' signifies a mirror created with '--nosync', while 'm'
signifies a mirror created w/o '--nosync') must be preserved when extending a
mirror created with '--nosync'. See #1 for example of 'M' attribute.
3) A mirror created without '--nosync' should extend with 'nosync' only when
'--nosync' is explicitly used when extending.
[EXAMPLE]# lvs vg; lvextend -L +5G vg/lv; lvs vg
LV VG Attr LSize Pool Origin Snap% Move Log Copy% Convert
lv vg mwi-a-m- 20.00m lv_mlog 100.00
Extending 2 mirror images.
Extending logical volume lv to 5.02 GiB
Logical volume lv successfully resized
LV VG Attr LSize Pool Origin Snap% Move Log Copy% Convert
lv vg mwi-a-m- 5.02g lv_mlog 0.39
vs.
[EXAMPLE]# lvs vg; lvextend -L +5G vg/lv --nosync; lvs vg
LV VG Attr LSize Pool Origin Snap% Move Log Copy% Convert
lv vg mwi-a-m- 20.00m lv_mlog 100.00
Extending 2 mirror images.
Extending logical volume lv to 5.02 GiB
Logical volume lv successfully resized
LV VG Attr LSize Pool Origin Snap% Move Log Copy% Convert
lv vg Mwi-a-m- 5.02g lv_mlog 100.00
4) The 'm' attribute must change to 'M' when extending a mirror created without
'--nosync' is extended with the '--nosync' option. (See #3 examples above.)
5) An inactive mirror's sync percent cannot be determined definitively, so it
must not be allowed to skip resync. Instead, the extend should ask the user if
they want to extend while performing a resync.
[EXAMPLE]# lvchange -an vg/lv
[EXAMPLE]# lvextend -L +5G vg/lv
Extending 2 mirror images.
Extending logical volume lv to 10.00 GiB
vg/lv is not active. Unable to get sync percent.
Do full resync of extended portion of vg/lv? [y/n]: y
Logical volume lv successfully resized
6) A mirror that is performing recovery (as opposed to an initial sync) - like
after a failure - is not allowed to extend with either an implicit or
explicit nosync option. [You can simulate this with a 'corelog' mirror because
when it is reactivated, it must be recovered every time.]
[EXAMPLE]# lvcreate -m1 -L 5G -n lv vg --nosync --corelog
WARNING: New mirror won't be synchronised. Don't read what you didn't write!
Logical volume "lv" created
[EXAMPLE]# lvs vg
LV VG Attr LSize Pool Origin Snap% Move Log Copy% Convert
lv vg Mwi-a-m- 5.00g 100.00
[EXAMPLE]# lvchange -an vg/lv; lvchange -ay vg/lv; lvs vg
LV VG Attr LSize Pool Origin Snap% Move Log Copy% Convert
lv vg Mwi-a-m- 5.00g 0.08
[EXAMPLE]# lvextend -L +5G vg/lv
Extending 2 mirror images.
Extending logical volume lv to 10.00 GiB
vg/lv cannot be extended while it is recovering.
7) If 'no' is selected in #5 or if the condition in #6 is hit, it should not
result in the mirror being resized or the 'm/M' attribute being changed.
NOTE: A mirror created with '--nosync' behaves differently than one created
without it when performing an extension. The former cannot be extended when
the mirror is recovering (unless in-active), while the latter can. This is
a reasonable thing to do since recovery of a mirror doesn't take long (at
least in the case of an on-disk log) and it would cause far more time in
degraded mode if the extension w/o '--nosync' was allowed. It might be
reasonable to add the ability to force the operation in the future. This
should /not/ force a nosync extension, but rather force a sync'ed extension.
IOW, the user would be saying, "Yes, yes... I know recovery won't take long
and that I'll be adding significantly to the time spent in degraded mode, but
I need the extra space right now!".
This patch also does some clean-up of the splitmirrors code.
I've attempted to clean-up the splitmirrors code to make it easier to
understand with fewer operations. I've tried to reduce the number of
metadata operations without compromising the intermediate stages which
are necessary for easy clean-up in the even of failure.
These changes now correctly handle cluster situations - including exclusive
cluster mirrors. Whereas before, a splitmirror operation would result in
remote nodes having LVM commands report the newly split LV with a proper
name while DM commands would report the old (pre-split) names of the device.
IOW, there was a kernel/userspace mismatch.
The original commit comments can be located via this git commit ID:
7d8e615c0b
There were three possible solutions to the original problem proposed in the
initial check-in. The one chosen was as follows:
2) Do like _remove_mirror_images does and suspend the original, then suspend
the sub-lv (the error target), then resume the sub-lv, and finally resume the
original LV. This seems like extra pointless operations to me, but it doesn't
produce the error message (although, I'm not sure why) and it allows us to
leave the visible flag in place.
Turns out, the cluster also views the extra suspend/resume operations as
pointless too and ignores them. So, this solution doesn't work in a cluster.
Further, I've noticed that in addition to the remote cluster nodes still getting
I/O errors from scanning the error target, they also have a different LVM and
DM views of the same LV. IOW, while the LVM level (gotten from the LVM metadata)
sees the correct name for the newly split LV, device-mapper still maintains the
old names.
Because the original fix failed to completely fix the problem (or work-around it)
and because a better solution must be found to address the additional cluster
issue of device renaming, I am reverting the above mentioned commit.
The current code does not always assign proper udev flags to sub-LVs (e.g.
mirror images and log LVs). This shows up especially during a splitmirror
operation in which an image is split off from a mirror to form a new LV.
A mirror with a disk log is actually composed of 4 different LVs: the 2
mirror images, the log, and the top-level LV that "glues" them all together.
When a 2-way mirror is split into two linear LVs, two of those LVs must be
removed. The segments of the image which is not split off to form the new
LV are transferred to the top-level LV. This is done so that the original
LV can maintain its major/minor, UUID, and name. The sub-lv from which the
segments were transferred gets an error segment as a transitory process
before it is eventually removed. (Note that if the error target was not put
in place, a resume_lv would result in two LVs pointing to the same segment!
If the machine crashes before the eventual removal of the sub-LV, the result
would be a residual LV with the same mapping as the original (now linear) LV.)
So, the two LVs that need to be removed are now the log device and the sub-LV
with the error segment. If udev_flags are not properly set, a resume will
cause the error LV to come up and be scanned by udev. This causes I/O errors.
Additionally, when udev scans sub-LVs (or former sub-LVs), it can cause races
when we are trying to remove those LVs. This is especially bad during failure
conditions.
When the mirror is suspended, the top-level along with its sub-LVs are
suspended. The changes (now 2 linear devices and the yet-to-be-removed log
and error LV) are committed. When the resume takes place on the original
LV, there are no longer links to the other sub-lvs through the LVM metadata.
The links are implicitly handled by querying the kernel for a list of
dependencies. This is done in the '_add_dev' function (which is recursively
called for each dependency found) - called through the following chain:
_add_dev
dm_tree_add_dev_with_udev_flags
<*** DM / LVM divide ***>
_add_dev_to_dtree
_add_lv_to_dtree
_create_partial_dtree
_tree_action
dev_manager_activate
_lv_activate_lv
_lv_resume
lv_resume_if_active
When udev flags are calculated by '_get_udev_flags', it is done by referencing
the 'logical_volume' structure. Those flags are then passed down into
'dm_tree_add_dev_with_udev_flags', which in turn passes them to '_add_dev'.
Unfortunately, when '_add_dev' is finding the dependencies, it has no way to
calculate their proper udev_flags. This is because it is below the DM/LVM
divide - it doesn't have access to the logical_volume structure. In fact,
'_add_dev' simply reuses the udev_flags given for the initial device! This
virtually guarentees the udev_flags are wrong for all the dependencies unless
they are reset by some other mechanism. The current code provides no such
mechanism. Even if '_add_new_lv_to_dtree' were called on the sub-devices -
which it isn't - entries already in the tree are simply passed over, failing
to reset any udev_flags. The solution must retain its implicit nature of
discovering dependencies and be able to go back over the dependencies found
to properly set the udev_flags.
My solution simply calls a new function before leaving '_add_new_lv_to_dtree'
that iterates over the dtree nodes to properly reset the udev_flags of any
children. It is important that this function occur after the '_add_dev' has
done its job of querying the kernel for a list of dependencies. It is this
list of children that we use to look up their respective LVs and properly
calculate the udev_flags.
This solution has worked for single machine, cluster, and cluster w/ exclusive
activation.
