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If the tools for checking thin_pool or cache metadata are missing,
issue rather just a WARNING, but let the operation of activation
continue.
This has the advantage, the if user is missing those tools,
but he already started to use thinpool or cacheing, he can
access these volumes with a WARNING.
Also if the user is using too old tools i.e. for CacheV2 format
dmpd tool 0.7 is required - provide informative WARNING and
skip failure from older tool version which can't understand
new format V2.
In case a newly created RaidLV is blacklisted using config
\"activation { volume list = [ ... ] }\" (i.e. its SubLVs stay inactive),
the metadata SubLVs can't get wiped thus failing the creation.
As a result, the RaidLV together with its SubLVs
is left behind in an inconsistent state.
Fix by removing the RaidLV and provide a hint about volume_list reasoning.
Resolves: rhbz1161347
Introduce prioritized_section() as a closer match to previous logic
of critical_section() that has been held over longer sequence of
ioctl commands - essentially it's matching operation on a single
cookie.
While 'critical_section()' now corresponds to locked memory - we hold
this memory only between suspend/resume thus notion of 'cookie' was
lost.
This patch restores some logic unintentionaly lost with dropping
memory locking for just activation/deactivation calls.
With these read errors it's useful to know the reason.
Also avoid to log error just once so we know exactly
how many times we did failing read.
On the other hand reduce repeated log_error() on code 'backtrace'
path and change severity of message to just log_debug() so the
actual read error is printed once for one read.
Just like lvm2 has internal devices like _tdata which is using UUID with
suffix, there is similar private type of device for crypto device where
they are using CRYPT-TEMP uuid prefix.
Also ignore stratis.
Some kernel version suffer from bad state transition where a device
steps into 'frozen' mode. Any application that tries to read such
raid gets unfortunatelly bloked.
As some sort of protection try to skip such raid device from being
scanned to minimize chances to block lvm2 command on such scan.
When such device is found, warning gets printed.
RaidLVs on read_only_volume_list have their SubLVs
activated readonly thus disabling metadata updates
or image resynchronization/recovery. Bug also causes
automatic repairs to fail.
Fix by always activating the RAID SubLVs readwrite.
Resolves: rhbz1208269
When snapshot is created in read-only mode with 'lvcreate -s -pr...',
lvm2 still needs to be able to write to layered -cow volume
to store metadata and exceptions blocks.
TODO: in some case we might be able to do full tree with read-only
volume but this probably needs futher validation:
1. checking snapshot header already exist
2. origin & snapshot are both in read-only mode.
Occasionaly users may need to peek into 'component devices.
Normally lvm2 does not let users activation component.
This patch adds special mode where user can activate
component LV in a 'read-only' mode i.e.:
lvchange -ay vg/pool_tdata
All devices can be deactivated with:
lvchange -an vg | vgchange -an....
Introduce:
lv_is_component() check is LV is actually a component device.
lv_component_is_active() checking if any component device is active.
lv_holder_is_active() is any component holding device is active.
Instead of checking with existing size of external origin LV,
use correctly the new 'wanted' size of this LV whether it fits
the limitiation requirements for older thin-pool target.
Otherwise code started to the the resize, updates metadata and
just fails during 'resize' in case the LV was active. For
inactive LV operation could have actually passed.
Fix missing 'externalLV' traversing for thins with external origins.
Replace extra for_each_sub_lv_except_pools() with better
internal logic allowing selectively to cut of processed subLV tree.
Extend error code for function 'fn()' when it returns -1 it will
stop futher tree scan for given LV.
Also a bit simplify code to have only one place that
is calling 'fn()' and use level counter to know
depth of traversing.
Update renaming travering to skip trees for pools
and external origins.
While 'file-locking' code always dropped cached VG before
lock was taken - other locking types actually missed this.
So while the cache dropping has been implement for i.e. clvmd,
actually running command in cluster keept using cache even
when the lock has been i.e. dropped and taken again.
This rather 'hard-to-hit' error was noticable in some
tests running in cluster where content of PV has been
changed (metadata-balance.sh)
Fix the code by moving cache dropping directly lock_vol() function.
TODO: it's kind of strange we should ever need drop_cached_metadata()
used in several places - this all should happen automatically
this some futher thinking here is likely needed.
Avoid using same return code for reporting 2 different things
and stricly report error code by return value and add new
parameter for reporting monitoring status.
This makes easier to recognize which error we got from dm_event
and continue only with ENOENT.
Check if the generated vg name still fits the buffer.
So too long strings are rejected.
Drop -1 from size passed to snprintf - as the \0 is already included.
With pthreaded daemons like 'dmeventd' using liblvm via plugin,
lvm2 actually should not 'play' with streams at all - as there
could be parallel outputs running.
As a current quick workaround just disable change for pthreaded
program (gettid() != getpid()).
TODO: it's possible the change of buffering actually doesn't serve us
any measurable benefit and could be dropped as whole later...
Meanwhile this patch is fixing this occasional valgrind race report:
Invalid read of size 4
at 0x571892C: vfprintf (in /usr/lib64/libc-2.26.9000.so)
by 0x57216B3: fprintf (in /usr/lib64/libc-2.26.9000.so)
by 0x5042886: dm_event_log (libdevmapper-event.c:925)
by 0x10B015: _dmeventd_log (dmeventd.c:125)
by 0x10D289: _unregister_for_event (dmeventd.c:1146)
by 0x10E52E: _handle_request (dmeventd.c:1583)
by 0x10E6D7: _do_process_request (dmeventd.c:1631)
by 0x10E7C6: _process_request (dmeventd.c:1660)
by 0x1101A4: main (dmeventd.c:2285)
Address 0x6264d30 is 192 bytes inside a block of size 552 free'd
at 0x4C2ED68: free (vg_replace_malloc.c:530)
by 0x573907D: fclose@@GLIBC_2.2.5 (in /usr/lib64/libc-2.26.9000.so)
by 0x6AC5C00: reopen_standard_stream (log.c:189)
by 0x6A8E62C: destroy_toolcontext (toolcontext.c:2271)
by 0x6BA5C22: lvm_fin (lvmcmdline.c:3339)
by 0x6BD5EF3: lvm2_exit (lvmcmdlib.c:123)
by 0x6856013: dmeventd_lvm2_exit (dmeventd_lvm.c:103)
by 0x66535B8: unregister_device (dmeventd_thin.c:432)
by 0x10CBBC: _do_unregister_device (dmeventd.c:926)
by 0x10CD74: _monitor_unregister (dmeventd.c:979)
by 0x10D094: _monitor_thread (dmeventd.c:1066)
by 0x54B35E0: start_thread (in /usr/lib64/libpthread-2.26.9000.so)
by 0x57C30EE: clone (in /usr/lib64/libc-2.26.9000.so)
Block was alloc'd at
at 0x4C2DBBB: malloc (vg_replace_malloc.c:299)
by 0x573932B: fdopen@@GLIBC_2.2.5 (in /usr/lib64/libc-2.26.9000.so)
by 0x6AC5DC2: reopen_standard_stream (log.c:200)
by 0x6A8D11D: create_toolcontext (toolcontext.c:1898)
by 0x6BA5B6B: init_lvm (lvmcmdline.c:3319)
by 0x6BD5BC8: cmdlib_lvm2_init (lvmcmdlib.c:34)
by 0x6BD5F04: lvm2_init (lvm2cmd.c:20)
by 0x6855EA7: dmeventd_lvm2_init (dmeventd_lvm.c:67)
by 0x665305F: register_device (dmeventd_thin.c:352)
by 0x10CB7A: _do_register_device (dmeventd.c:916)
by 0x10CEE4: _monitor_thread (dmeventd.c:1006)
by 0x54B35E0: start_thread (in /usr/lib64/libpthread-2.26.9000.so)
by 0x57C30EE: clone (in /usr/lib64/libc-2.26.9000.so)
....
Process terminating with default action of signal 6 (SIGABRT): dumping core
at 0x570016B: raise (in /usr/lib64/libc-2.26.9000.so)
by 0x5701520: abort (in /usr/lib64/libc-2.26.9000.so)
by 0x57437D8: __libc_message (in /usr/lib64/libc-2.26.9000.so)
by 0x5743831: __libc_fatal (in /usr/lib64/libc-2.26.9000.so)
by 0x5744056: _IO_vtable_check (in /usr/lib64/libc-2.26.9000.so)
by 0x574751C: __overflow (in /usr/lib64/libc-2.26.9000.so)
by 0x574191A: fputc (in /usr/lib64/libc-2.26.9000.so)
by 0x50428E3: dm_event_log (libdevmapper-event.c:934)
by 0x10B015: _dmeventd_log (dmeventd.c:125)
by 0x10D289: _unregister_for_event (dmeventd.c:1146)
by 0x10E52E: _handle_request (dmeventd.c:1583)
by 0x10E6D7: _do_process_request (dmeventd.c:1631)
by 0x10E7C6: _process_request (dmeventd.c:1660)
by 0x1101A4: main (dmeventd.c:2285)
Some tools are typically installed into /usr/sbin (or /sbin) dir.
And some systems do not add this path to user's $PATH var.
Ensure sbin paths are looked through...
In fact pvmove does support 'clustered-core' target for clustered
pvmove of LVs activated on multiple nodes.
This patch restores support for activation of pvmove on all nodes
for LVs that are also activate on all nodes.
Add protectional internall error whenever we spot activation
of 'exclusive' only segments in 'non-exclusive' mode.
TODO: possibly the activation locking could be enhanced to handle
this fully behind the scene - as for now this works purely for
lvchange/vgchange activation.
Use properly exclusive activation when reactivating origin after
snapshot merge (since origin must have been previously also exlusively
activated).
Same applies when converting volumes to thin-pool or cache.
Previously used 'only' local activation incorrectly allowed local
activation of some targets (i.e. raid) - thus 'leaking' chance to
activate same device on another node - which can be a problem
for device types like raid.
If the data being requested is present in last_[extra_]devbuf,
return that directly instead of reading it from disk again.
Typical LVM2 access patterns request data within two adjacent 4k blocks
so we eliminate some read() system calls by always reading at least 8k.
If it obtains the data, it passes it into the supplied callback function
and returns 1. Otherwise the callback receives failed = 1.
Updated config_file_read_fd to use this and similarly return the data
via a callback fn of its own.
Rename dev_read() to dev_read_buf() - the function that reads data
into a supplied buffer.
Introduce a new dev_read() that allocates the buffer it returns and
switch the important users over to this. No caller may change the
returned data. (For now, callers are responsible for freeing it after
use, but later the device layer will take full ownership.)
dev_read_buf() should only be used for tiny buffers or unimportant code
(such as the old disk formats).
If there is sufficient space in the metadata area, align the next
metadata to a disk offset that is a multiple of 4096 bytes and
don't write it circularly. If it doesn't all fit at the end
of the metadata area, go back to the start and write it all there
contiguously.
If there is insufficient space to use the new stricter rules, revert to
the original behaviour, aligning on 512-byte boundaries wrapping around
the circular buffer as required.
Even after writing some metadata encountered problems, some commands
continue (rightly or wrongly) and attempt to make further changes.
Once an mda is marked MDA_FAILED, don't try to use it again.
This also applies when reverting, where one loop already skips
failed mdas but the other doesn't.
This fixes some device open_count warnings on relevant failure paths.
Use new ALIGN_ABSOLUTE macro when calculating the start location
of new metadata and adjust the end of buffer detection so that
there is no longer an imposed gap between old and new metadata.
lvmdbusd executable script must use python3 interpreter detected by
configure script, as site-packages directory used for library is only
used by that interpreter.
Introduce enum dev_io_reason to categorise block device I/O
in debug messages so it's obvious what it is for.
DEV_IO_SIGNATURES /* Scanning device signatures */
DEV_IO_LABEL /* LVM PV disk label */
DEV_IO_MDA_HEADER /* Text format metadata area header */
DEV_IO_MDA_CONTENT /* Text format metadata area content */
DEV_IO_FMT1 /* Original LVM1 metadata format */
DEV_IO_POOL /* Pool metadata format */
DEV_IO_LV /* Content written to an LV */
DEV_IO_LOG /* Logging messages */
When entering any critical section, lvm2 used to lock process memory
and raised task priority to avoid problem with page swapping and minimize
time of having non-resumed devices in table.
With this patch, memory locking which which is expensive is only used when
entering 'suspending' section as only in this section there is risk
lvm could be suspending a device which later can be needed for paging.
Raised priority is still kept for all section entrances as this is
low-cost operation and may accelerate table resumes - although the real
impact can be still considered later.
When pvmove is finished and metadata are updated, the code missed
to merge possible mergable segments - so add explicit merging
call after pvmoved volumes are unlocked.
This avoids weird results where i.e. lvs could have been reporting
non-matching segments as lvs upon metadata read is doing silent segment
merging while dm table left after pvmove was still preserving
non-merged segments.
When large size number (>2^31) is given on command line it could be
misdetected and in certain cases lead to wrongly casted number.
So make sure all cases always do set _MAX number in case the value would
not fit within the supported range instead of getting some random value
within the range.
In most cases this was not a problem to detect, but i.e. stripesize
parameter might have been fooled by certain large numbers.
Rewrite validation of stripes and stripe_size args into more readable
sequential code.
Extend reading of stripes & stripes_size args so it better knows
defaults for types like striped raid.
TODO: this should really be a value obtained for segtype structure and
all the weird conditions and modification of stripes and stripe_size
around lvm2 code should be dropped.
When pvmove is finished and does 'suspend/resume' on PVMOVE LV,
on resume path committed metadata are already showing 'standalone'
pvmove LV prepared just for removal.
However code should be able to 'resume' preloaded LV there were
participating in pvmove operation.
Previously this was all done in the 'tools' part of lvm2 code.
So the lvconvert upon pvmove finish had to explicitely call 'resume' on every such LV.
Now 'smarted' activation code is able to deduce and combine all information from
the active dm table and committed metadata so single call resolves
it all in one go.
Internally holders are detected by reading sysfs directory to capture
all needed UUID which are then looked in lvm2 metadata and all such
LVs are automatically collected into dmtree.
Only thin-pool with origin_only suspend is allowed to be not suspending anything.
In such case pairing resume will 'decrement' critical section counter.
Just like suspend handles preload for pvmove finish,
in similar way handle suspend of starting pvmove.
In this case the precommited metadata are checked for list of PVMOVEed
LVs and those are suspended in with committed metadata.
When activation of LVs fails prior pvmove start, try to deactivate
already activated LVs.
TODO: possibly remember which LVs where already activate and only those
take down - devices which are already in-use will stay active.
Only lv_committed() now uses vg->vg_committed and it appears redundant
if its contents match the enclosing VG so don't waste cycles creating it
when that's known to be true when no write lock is held so the struct
won't get modified.
The persistent filter should not be imported by any command that doesn't
use it so take addtional note of REQUIRES_FULL_LABEL_SCAN (for vgrename)
and introduce IGNORE_PERSISTENT_FILTER for vgscan and pvscan.
In HA cluster, we have "clvm" resource agent to manage clvmd daemon.
The agent invokes clvmd like: "clvmd -T90 -d0", which always prints
a scaring error message:
"""
local socket: connect failed: No such file or directory
"""
When specifed with "-d" option, clvmd tries to check if an instance
of the clvmd daemon is already running through a testing connection.
The connect() will fail with this ENOENT error in such case, so supress
the error message in such case.
TODO: add missing error reaction code - since ofter log_error, program
is not supposed to continue running (log_error() is for reporting
stopping problems).
Signed-off-by: Eric Ren <zren@suse.com>
Check and prevent starting another snapshot merge before
exiting merging is finished.
TODO: we can possibly implement smarter logic to drop existing
merging and start a new one.
We always preferred and recommended socket activation for our services
so remove the Install section in related .service units which are unused
in this case and keep only the Install section in associated .socket
units.
Signed-off-by: Bastian Blank <waldi@debian.org>
Since 4fa5add6b1 ("pvcreate: Wipe cached
bootloaderarea when wiping label.") label_remove is responsible
for the lvmcache_del. (toollib and liblvm need fixing to share
the code.)
Correct reported message when thin snapshot has been already merged.
So lvm2 is no longer reporting "Mergins of snapshot X will occur..."
(even with swapped names).
When an ignored metadata area gets flagged for use again, make sure the
code doesn't try to parse its old metadata. Firstly by trying to detect
this situation and skipping the read (while still remembering the
position reached in the circular buffer), and secondly by clearing the
invalid live metadata location on disk as a precaution when subsequently
writing out the precommitted metadata.
Problems showed up when a metadata area in one VG got moved to
another VG in ignored state (still holding metadata for the original
VG) and then later got brought into use in the new VG - only the header
should be read in this case, not any of the metadata content.
vgsplit shares the vg_rename code so that must only set the PV_MOVED_VG
flag introduced in commit 486ed10848
("vgmerge: Fix intermediate metadata corruption") on PVs that moved.
Last patch missed to mention, we've improved/fixed generated paths
in units and init.d shell scripts when lvm2 was plainly configured
with just i.e. --prefix.
Note: some distros might have fully specified --sbindir and
--usrsbindir - thus those very not seeing problems in generated paths.
Do not allow to take snapshot of mirror/raid leg or log or metadata LV.
This was actually never supported, but user was able to create it,
and this put device stack in hardly fixable state (needs manual work).
This prevents such creation to pass.
Also improve validation when recreating snapshot volume type
from origin and COW volume.
Correction to function for extracting vgname out of lvconvert
parameters.
Avoid repeating some checks.
Add code to handle generic options which may provide vgname in its argument
and compare them all so they match to a single vgname (otherwise it's a
error).
Extract default (envvar) vgname only when no position nor optional vgname is
found.
Fixing regression instroduce with patchset started with commit:
1e2420bca8 (2.02.169)
lvcreate supports a 'conversion' when caching LV.
This normally worked fine, however in case passed LV was
thin-pool's data LV with suffix _tdata we have failed to early.
As the easiest fix looks dropping validation of name when
caching type is select - such name check will happen later
once the VG is opened again and properly detect if the LV
with protected name already exists and can be converted,
or will be rejected as ambigiuous operation requiring user
to specify --type cache | --type cache-pool.
Replaced the confusing device error message "not found (or ignored by
filtering)" by either "not found" or "excluded by a filter".
(Later we should be able to say which filter.)
Left the the liblvm code paths alone.
Activation lock has a primary purpose to serialize locking of individual
LV in case there is no other protecting mechanism for parallel
execution.
However in the case an activated LV is composed from several other LVs,
noone should be able to manipulate with those LVs as well.
This patch add a very 'naive' global VG activation locking in this case.
In the future we may introduce smarter function detecting minimal closed
graph components if this will appear as bottleneck
Patch checks if the VG Write lock is held - in this case we do not
need any more locking - command has exclusive access to VG.
In case we have clustered VG and we are activating an LV which does not
need other LVs - we also do not need any more locks.
In all other cases take respective lock - for single LV - use lvid,
for complex LVs use vgname.
vgmerge suffers from a similar problem to the one fixed in commit
8146548d25 ("vgsplit: Fix intermediate
metadata corruption.")
When merging, splitting or renaming VGs, use a new PV status flag
PV_MOVED_VG to mark the PVs that hold metadata with the old VG name and
use this to provide PV-level granularity instead of incorrectly assuming
all PVs in the VG are the same.
Changing the VG of a PV uses the same on-disk mechanism as vgrename.
This relies on recognising both the old and new VG names. Prior to this
patch the vgsplit code incorrectly provided the new VG name twice
instead of the old and new ones. This lead the low-level mechanism not
to recognise the device as already belonging to a VG and so paying no
attention to the location of its existing metadata, sometimes partly
overwriting it and then later trying to read the corrupt metadata and
issuing a checksum error.
In a shared VG, only allow pvmove with a named LV,
so that only PE's used by the LV will be moved.
The LV is then activated exclusively, ensuring that
the PE's being moved are not used from another host.
Previously, pvmove was mistakenly allowed on a full PV.
This won't work when LVs using that PV are active on
other hosts.
Enable handling of --poolmetadataspare so if user can prevent
creation of _pmspare volume during --repair operation (just
like during actual lvcreate or lvconvert) for pool volumes.
When file-locking mode failed on locking, such description was leaked
(typically not an issue since command usually exists afterwards).
So shirt close() at the end of function and use it in all error paths.
Also make sure, when interrrupt is detected, it's really not holding
lock and returns 0.
Fix code checking that the 2nd mda which is at the end of disk really
fits the available free space and avoid any DA and MDA interleaving when
we already have DA preallocated. This mainly applies when we're restoring
a PV from VG backup using pvcreate --restorefile where we may already have
some DA preallocated - this means the PV was in a VG before with already
allocated space from it (the LVs were created). Hence we need to avoid
stepping into DA - the MDA can never ever be inside in such case!
The code responsible for this calculation was already in
_text_pv_add_metadata_area fn, but it had a bug in the calculation where
we subtracted one more sector by mistake and then the code could still
incorrectly allocate the MDA inside existing DA. The patch also renames
the variable in the code so it doesn't confuse us in future.
Also, if the 2nd mda doesn't fit, don't silently continue with just 1
MDA (at the start of the disk). If 2nd mda was requested and we can't
create that due to unavailable space, error out correctly (the patch
also adds a test to shell/pvcreate-operation.sh for this case).
If the PV was originally created with a larger-than-default
metadata area the restored one wasn't and might not even be
large enough to hold the metadata!
Previously the cache remembered an existing bootloaderarea and
reinstated it (without even checking for overlap) when asked to
write out the PV. pvcreate could write out an incorrect layout.
Avoid adding -g more then once for debug builds.
Avoid enabling DEBUG_MEM when we build multithreaded tools.
Link executables with -fPIE -pie and --export-dynamic LDFLAGS
Introduce PROGS_FLAGS to add option to pass flags for external libs.
Link lvm2 internally library only when really used.
Link DAEMON_LIBS with daemons.
Pass VALGRIND_CFLAGS internally
Set shell failure mode on couple places.
lvm2 warned about zeroing and too big chunksize (>=512KiB), but
only during lvconvert, so lvcreate was creating thin-pools
without any warning about possible slowness of thin provisioning
because of zeroing.
Since _deactivate_and_remove_lvs() is used in more then one place,
move the needed udev synchronization into this function so other
users automatically get correct fs state before next dm manipulation.
Assumption here is that this udev synchronization 'delay' may also
prevent to 'early' table reloads which might cause kernel problems
for md-core - but we may need more generic time-limited reload
frequency for raid devices.
Note: on udev-less system there will be almost no delay.
Since we are reading size as (double) we can get way bigger
number then just plain int64. So to make this check actually
more valid and usable do a maxsize compare in 'double'.
Initialize mutex upfront any debugging and fix this report:
Mutex reinitialization: mutex 0x485d20, recursion count 0, owner 1.
at 0x4C38480: pthread_mutex_init_intercept (drd_pthread_intercepts.c:821)
by 0x4C38480: pthread_mutex_init (drd_pthread_intercepts.c:830)
by 0x11F359: main (clvmd.c:562)
mutex 0x485d20 was first observed at:
at 0x4C38F63: pthread_mutex_lock_intercept (drd_pthread_intercepts.c:885)
by 0x4C38F63: pthread_mutex_lock (drd_pthread_intercepts.c:898)
by 0x11E920: debuglog (clvmd.c:254)
by 0x11F1D8: main (clvmd.c:527)
Switch from warn to log_error since this generated
failing return code for command so printing log_error()
is mandatory.
Happens with i.e. pvscan --cache meets crashing lvmetad.
Centralise editing of the client list into _add_client() and
_del_client(). Introduce _local_client_count to track the size of the
list for debugging purposes. Simplify and standardise the various ways
the list gets walked.
While processing one element of the list in main_loop(),
cleanup_zombie() may be called and remove a different element, so make
sure main_loop() refreshes its list state on return. Prior to this
patch, the list edits for clients disappearing could race against the
list edits for new clients connecting and corrupt the list and cause a
variety of segfaults.
An easy way to trigger such failures was by repeatedly running shell
commands such as:
lvs &; lvs &; lvs &;...;killall -9 lvs; lvs &; lvs &;...
Situations that occasionally lead to the failures can be spotted by
looking for 'EOF' with 'inprogress=1' in the clvmd debug logs.
lvm_run needs to place NULL as the last element into argv[].
Otherwise we get:
Conditional jump or move depends on uninitialised value(s)
_command_required_pos_matches (lvmcmdline.c:1443)
_find_command (lvmcmdline.c:1610)
lvm_run_command (lvmcmdline.c:2770)
lvm2_run (lvmcmdlib.c:91)
When raid leg rimage device is marked as 'D'ead by mdcore,
lvm2 was not able to replace such device with allocate policy,
as device has not appared as missing.
Add detection of transiently failing devices.
Basically reverting commit 58a9f88b8c.
We can use origin_only in case we are snapshot's origin,
as we do support this stack.
So when we are 'uncaching' origin+snaps - we do need to reload only
origin and we do not need to play with snaps.
'lvdisplay -m' tried to go through NULL policy settings,
when such policy was not defined for CachedLV.
Patch is fixing display of cache-pool without defined settings,
as this is now a valid pool and we mostly want users to define
these settings when actually really caching a LV.
Since cache LV can be a stacked device, there is no real reason
trying to use slight optimised tree for origin_only cache reload
(it could be even wrongly implemented in this case).
We can easily go with stardard tree load here.
When user runs command like 'lvconvert --splitcache' the operation
might be actually either slow or not making any progress in kernel,
so lets give user a chance to abort such operation.
When user press 'Ctrl+C' device table is restored to pre-flushing state.
