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More efficient spare volume creation. Save 1 extra commit
and properly activate this volume according to our cluster
activation rules (using lv_active_change() for this).
Since we 'layer' for cache origin which and we support dropping
cache layer - we need to restore origin name in case
the origin LV is more complex target - i.e. raid.
Drop _corig from name
Cleanup and rename parent -> parent_lv.
Revert part of commit 51a29e6056,
it's probably bad idea to continue with any recovery, when
vg_write() or vg_commit() fail - so it's better to leave it as it is.
Let's use this function for more activations in the code.
'needs_exlusive' will enforce exlusive type for any given LV.
We may want to activate LV in exlusive mode, even when we know
the LV (as is) supports non-exlusive activation as well.
lvcreate -ay -> exclusive & local
lvcreate -aay -> exclusive & local
lvcreate -aly -> exclusive & local
lvcreate -aey -> exclusive (might be on any node).
Call check_new_thin_pool() to detect in-use thin-pool.
Save extra reactivation of thin-pool when thin pool is not active.
(it's now a bit more expensive to invoke thin_check for new pools.)
For new pools:
We now active locally exclusively thin-pool as 'public' LV.
Validate transaction_id is till 0.
Deactive.
Prepare create message for thin-pool and exclusively active pool.
Active new thin LV.
And deactivate thin pool if it used to be inactive.
Replace lv_cache_block_info() and lv_cache_policy_info()
with lv_cache_status() which directly returns
dm_status_cache structure together with some calculated
values.
After use mem pool stored inside lv_status_cache structure
needs to be destroyed.
Add API call to calculate extents from percentage value.
Size is based in DM_PERCENT_1 units.
(Supporting decimal point number).
This commit is preparing functionality for more global
usage of % with i.e. --size option.
Unlike with thin-pool - with cache we support all args also
directly when create cache volume.
So the result of 'separate' cache-pool creation and setting its
options should give same result as specifying those args
during cache creation.
Cache-pool values are used as defaults if the params are
not specified with cache creation.
Move code for creation of thin volume into a single place
out of lv_extend(). This allows to drop extra pool arg
for alloc_lv_segment() && lv_extend() and makes code
more easier to read and follow.
When we create volumes with chunk size bigger then extent size
we try to round up to some nearest chunk boundary.
Until now we did this for thins - use same logic for
cache volumes.
Refactor lvcreate code.
Prefer to use arg_outside_list_is_set() so we get automatic 'white-list'
validation of supported options with different segment types.
Drop used lp->cache, lp->cache and use seg_is_cache(), seg_is_thin()
Draw clear border where is the last moment we could change create
segment type.
When segment type is given with --type - do not allow it to be changed
later.
Put together tests related to individual segment types.
Finish cache conversion at proper part of lv_manip code after
the vg_metadata are written - so we could correcly clean-up created
stripe LV for cache volume.
Move test for size of new LV names in front before
any creation of LV.
Properly check striped segtype kernel presence,
since passed 'segtype' is already tested.
Keep deactivation error path local to wiping part of the function.
Create metadata with temporary flag (it's activated, zeroed
and deactivated).
Introduce new option to specify pool data size.
This will be user to create i.e. cache & cachepool at once.
And possible for thin external origin snapshot.
This is only very basic patch to enable options, the
real working code will come later.
We want to print smarter warning message only when
the zeroing was not provided on the first zeroable segment
of newly created LV.
Put warning within _should_wipe_lv function to avoid reevaluation
of same conditions twice.
Hide creation of temporary LVs and print them only in verbose mode.
e.g. hides confusing message about creation of _pmspare
device during creation of pool.
Ask for lock the proper LV.
Use the top-most LV to query for locally exclusive lock.
The rest of operations are then using 'lv_info()'
TODO:
Check all devices are reloaded from proper level.
In general any query on lv_is_active is supposed to be running
ona lv_lock_holder() volume.
Instead of segtype->ops->name() introduce lvseg_name().
This also allows us to leave name() function 'empty' for default
return of segtype->name.
TODO: add functions for rest of ops->
When we are given an existing LV name - it needs to be allowed
to pass in even restricted name as the LV could have existed
long before we introduced some new restriction on prefix/suffix.i
Fix the regression on name limits and drop restriction to be applied
on any existing LVs - only the new created LV names have to be
complient with current name restrictions.
FIXME: we are currently using restricted names incorrectly in few
other places - device_is_usable() skips restricted names,
and udev flags are also incorrectly set for restricted names
so these LVs are not getting links properly.
find_pv_in_vg fn iterates over the list of PVs covered by the VG and
each PV's pvl->pv->dev is compared with device acquired from device
cache. However, in case pvl->pv->dev is NULL as well as device cache
returns NULL (e.g. when device is filtered), we'll get incorrect match
and the code calling find_pv_in_vg uses incorrect PV (as it thinks
it's the exact PV with the pv_name). The INTERNAL_ERROR covers this
situation and errors out immediately.
The warnings arg was used to enable logging of warnings
when reading a PV. This arg is turned into a set of flags
with the WARN_PV_READ flag matching the existing behavior.
A new flag WARN_INCONSISTENT is added that will cause
vg_read_internal() to log the "VG is not consistent"
warning so the various callers do not need to log
this warning themselves.
A new vg_read flag READ_WARN_INCONSISTENT is used from
reporting to enable the WARN_INCONSISTENT flag in
vg_read_internal.
[Committed by agk with cosmetic changes and tweaks.]
Process PVs by iterating through VGs, then iterating through
devices if the command needs to process non-PV devices.
The process_single function can always use the VG and PV args.
[Committed by agk with cosmetic changes and tweaks.]
Introduce pool function for validation of chunk size.
It's good idea to be able to reject invalid chunk size
when entered on command line before we open VG.
Move code to better locations.
Improve test and remove invalid ones
(i.e. no reason to require cache size to be >= then origin).
Correctly comment where the code is doing actual conversion
of other existing volume - we do already a similar thing with
external origins.
Lots of new command line options and combinations is now supported.
Hopefully older syntax still works as well.
lvcreate --cache --cachepool vg/pool -l1
lvcreate --type cache --cachepool vg/pool -l1
lvcreate --type cache-pool vg/pool -l1
lvcreate --type cache-pool --name pool vg -l1
... and many many more ...
Since _pmspare is internal volume move it to
lv_remove_single - so it's automatically removed with
last remove thin-pool.
lv_remove_with_dependencies() is not always used for pool removal.
The cache mode of a new cache pool is always explicitly
included in the vg metadata. If a cache mode is not
specified on the command line, the cache mode is taken
from lvm.conf allocation/cache_pool_cachemode, which
defaults to "writethrough".
The cache mode can be displayed with lvs -o+cachemode.
There are actually three filter chains if lvmetad is used:
- cmd->lvmetad_filter used when when scanning devices for lvmetad
- cmd->filter used when processing lvmetad responses
- cmd->full_fiilter (which is just cmd->lvmetad_filter + cmd->filter chained together) used
for remaining situations
This patch adds the third one - "cmd->full_filter" - currently this is
used if device processing does not fall into any of the groups before,
for example, devices which does not have the PV label yet and we're just
creating a new one or we're processing the devices where the list of the
devices (PVs) is not returned by lvmetad initially.
Currently, the cmd->full_filter is used exactly in these functions:
- lvmcache_label_scan
- _pvcreate_check
- pvcreate_vol
- lvmdiskscan
- pvscan
- _process_each_label
If lvmetad is used, then simply cmd->full_filter == cmd->filter because
cmd->lvmetad_filter is NULL in this case.
We are not using already defined segement type names where we could.
There is a lot of other places in device-mapper and LVM2 we have those
hardcoded so we should better finally have a common interface in
libdevmapper to avoid this.
Use of lv_info() internally in lv_check_not_in_use(),
so it always could use with_open_count properly.
Skip sysfs() testing in open_count == 0 case.
Accept just 'lv' pointer like other functions.
The function has 'built-in' lv_is_active_locally check,
which however is not what we need to check in many place.
For now at least remotely active snapshot merge is
detected and for this case merge on next activation is scheduled.
We use adjusted_mirror_region_size() in two different contexts.
Either on command line -
here we do want to inform user about reduction of size.
Or in pvmove activation context -
here we should only use 'verbose' info.
When requesting to reload an LV imrove this API to
automatically reload its lock holding LV as in cluster
only top-level LVs are addressable with lock.
When vg_ondisk is NULL we do not need to search
through the whole VG to find out the same LV.
NOTE: as of now - VG locking is not enabled as some code parts
are breaking memory locking rules (lvm2app).
Once we enforce VG locking for read-only commands the effect
will be much better for larger VGs.
If we want to support conversion of VG to clustered type,
we currently need to relock active LV to get proper DLM lock.
So add extra loop after change of VG clustered attribute
to exlusively activate all active top level LVs.
When doing change -cy -> -cn we should validate LVs are not
active on other cluster nodes - we could be sure about this only
when with local exclusive activation - for other types
we require user to deactivate volumes first.
As a workaround for this limitation there is always
locking_type = 0 which amongs other skip the detection
of active LVs.
FIXME:
clvmd should handle looks for cluster locking type all the time.
While we could probably reacquire some type of lock when
going from non-clustered to clustered vg, we don't have any
single road back to drop the lock and keep LV active.
For now keep it safe and prohibit conversion when LV
is active in the VG.
Try to enforce consistent macro usage along these lines:
lv_is_mirror - mirror that uses the original dm-raid1 implementation
(segment type "mirror")
lv_is_mirror_type - also includes internal mirror image and log LVs
lv_is_raid - raid volume that uses the new dm-raid implementation
(segment type "raid")
lv_is_raid_type - also includes internal raid image / log / metadata LVs
lv_is_mirrored - LV is mirrored using either kernel implementation
(excludes non-mirror modes like raid5 etc.)
lv_is_pvmove - internal pvmove volume
Use lv_is_* macros throughout the code base, introducing
lv_is_pvmove, lv_is_locked, lv_is_converting and lv_is_merging.
lv_is_mirror_type no longer includes pvmove.
Use lv_update_and_reload() and lv_update_and_reload_origin()
to handle write/suspend/commit/resume sequence.
In few places this properly handle vg_revert() after suspend failure,
and also ensures there is metadata backup after successful vg_commit().
Fix rename operation for snapshot (cow) LV.
Only the snapshot's origin has the lock and by mistake suspend
and resume has been called for the snapshot LV.
This further made volumes unusable in cluster.
So instead of suspend and resuming list of LVs,
we need to just suspend and resume origin.
As the sequence write/suspend/commit/resume
is widely used in lvm2 code base - move it to
new lv_update_and_reload function.
Fixing problem, when user sets volume_list and excludes thin pools
from activation. In this case pool return 'success' for skipped activation.
We need to really check the volume it is actually active to properly
to remove queued pool messages. Otherwise the lvm2 and kernel
metadata started to go async since lvm2 believed, messages were submitted.
Add also better check for threshold when create a new thin volume.
In this case we require local activation of thin pool so we are able
to check pool fullness.
This patch makes the keyword combinations found in "lv_layout" and
"lv_role" much more understandable - there were some ambiguities
for some of the combinations which lead to confusion before.
Now, the scheme used is:
LAYOUTS ("how the LV is laid out"):
===================================
[linear] (all segments have number of stripes = 1)
[striped] (all segments have number of stripes > 1)
[linear,striped] (mixed linear and striped)
raid (raid layout always reported together with raid level, raid layout == image + metadata LVs underneath that make up raid LV)
[raid,raid1]
[raid,raid10]
[raid,raid4]
[raid,raid5] (exact sublayout not specified during creation - default one used - raid5_ls)
[raid,raid5,raid5_ls]
[raid,raid5,raid6_rs]
[raid,raid5,raid5_la]
[raid,raid5,raid5_ra]
[raid6,raid] (exact sublayout not specified during creation - default one used - raid6_zr)
[raid,raid6,raid6_zr]
[raid,raid6,raid6_nc]
[raid,raid6,raid6_ns]
[mirror] (mirror layout == log + image LVs underneath that make up mirror LV)
thin (thin layout always reported together with sublayout)
[thin,sparse] (thin layout == allocated out of thin pool)
[thin,pool] (thin pool layout == data + metadata volumes underneath that make up thin pool LV, not supposed to be used for direct use!!!)
[cache] (cache layout == allocated out of cache pool in conjunction with cache origin)
[cache,pool] (cache pool layout == data + metadata volumes underneath that make up cache pool LV, not supposed to be used for direct use!!!)
[virtual] (virtual layout == not hitting disk underneath, currently this layout denotes only 'zero' device used for origin,thickorigin role)
[unknown] (either error state or missing recognition for such layout)
ROLES ("what's the purpose or use of the LV - what is its role"):
=================================================================
- each LV has either of these two roles at least: [public] (public LV that users may use freely to write their data to)
[public] (public LV that users may use freely to write their data to)
[private] (private LV that LVM maintains; not supposed to be directly used by user to write his data to)
- and then some special-purpose roles in addition to that:
[origin,thickorigin] (origin for thick-style snapshot; "thick" as opposed to "thin")
[origin,multithickorigin] (there are more than 2 thick-style snapshots for this origin)
[origin,thinorigin] (origin for thin snapshot)
[origin,multithinorigin] (there are more than 2 thin snapshots for this origin)
[origin,extorigin] (external origin for thin snapshot)
[origin,multiextoriginl (there are more than 2 thin snapshots using this external origin)
[origin,cacheorigin] (cache origin)
[snapshot,thicksnapshot] (thick-style snapshot; "thick" as opposed to "thin")
[snapshot,thinsnapshot] (thin-style snapshot)
[raid,metadata] (raid metadata LV)
[raid,image] (raid image LV)
[mirror,image] (mirror image LV)
[mirror,log] (mirror log LV)
[pvmove] (pvmove LV)
[thin,pool,data] (thin pool data LV)
[thin,pool,metadata] (thin pool metadata LV)
[cache,pool,data] (cache pool data LV)
[cache,pool,metadata] (cache pool metadata LV)
[pool,spare] (pool spare LV - common role of LV that makes it used for both thin and cache repairs)
The 'lv_type' field name was a bit misleading. Better one is 'lv_role'
since this fields describes what's the actual use of the LV currently -
its 'role'.
Sort out the lvresize calculation code to handle size changes
specified as physical extents as well as logical extents
and to process mirror resizing and raid extensions correctly.
The 'approx alloc' option was masking the underlying problem.
The lv_type_name function is remnant from old code that reported
only single string for the LV type. LV types are now reported
in a more extended way as keyword list that describe the type
precisely (using lv_layout_and_type fn).
The lv_type_name was used in some error messages to display the
type of the LV so just reinstate the old messages back referencing
the type directly with a string - this is enough for error messages.
They don't need to display the LV type as precisely as it's used
on lvs output (which is optimized for selection anyway).
$ lvs -a -o name,vg_name,attr,layout,type
LV VG Attr Layout Type
lvol0 vg -wI-a----- linear linear
[pvmove0] vg p-C-aom--- mirror mirror,pvmove
(added "mirror" for pvmove LV)
$ lvs -a -o name,vg_name,attr,layout,type
LV VG Attr Layout Type
lvol0 vg ori------- linear external,multiple,origin,thin
[lvol1_pmspare] vg ewi------- linear metadata,pool,spare
lvol2 vg Vwi-a-tz-- thin snapshot,thin
lvol3 vg Vwi-a-tz-- thin snapshot,thin
pool vg twi-a-tz-- pool,thin pool,thin
[pool_tdata] vg Twi-ao---- linear data,pool,thin
[pool_tmeta] vg ewi-ao---- linear metadata,pool,thin
(added "multiple" for external origin used for more than one
thin snapshot - lvol0 in the example above)
Thin snapshots having external origins missed the "snapshot" keyword for
lv_type field. Also, thin external origins which are thin devices (from
another pool) were not recognized properly.
For example, external origin itself can be either non-thin volume (lvol0
below) or it can be a thin volume from another pool (lvol3 below):
Before this patch:
$ lvs -o name,vg_name,attr,pool_lv,origin,layout,type
Internal error: Failed to properly detect layout and type for for LV vg/lvol3
Internal error: Failed to properly detect layout and type for for LV vg/lvol3
LV VG Attr Pool Origin Layout Type
lvol0 vg ori------- linear external,origin,thin
lvol2 vg Vwi-a-tz-- pool lvol0 thin thin
lvol3 vg ori---tz-- pool unknown external,origin,thin,thin
lvol4 vg Vwi-a-tz-- pool1 lvol3 thin thin
pool vg twi-a-tz-- pool,thin pool,thin
pool1 vg twi-a-tz-- pool,thin pool,thin
- lvol2 as well as lvol4 have missing "snapshot" in type field
- lvol3 has unrecognized layout (should be "thin"), but has double
"thin" in lv_type which is incorrect
- (also there's double "for" in the internal error message)
With this patch applied:
$ lvs -o name,vg_name,attr,pool_lv,origin,layout,type
LV VG Attr Pool Origin Layout Type
lvol0 vg ori------- linear external,origin,thin
lvol2 vg Vwi-a-tz-- pool lvol0 thin snapshot,thin
lvol3 vg ori---tz-- pool thin external,origin,thin
lvol4 vg Vwi-a-tz-- pool1 lvol3 thin snapshot,thin
pool vg twi-a-tz-- pool,thin pool,thin
pool1 vg twi-a-tz-- pool,thin pool,thin
The maximum stripe size is equal to the volume group PE size. If that
size falls below the STRIPE_SIZE_MIN, the creation of RAID 4/5/6 volumes
becomes impossible. (The kernel will fail to load a RAID 4/5/6 mapping
table with a stripe size less than STRIPE_SIZE_MIN.) So, we report an
error if it is attempted.
This is very rare because reducing the PE size down that far limits the
size of the PV below that of modern devices.
metadata/lv_manip.c:269: warning: declaration of "snapshot_count" shadows a global declaration
There's existing function called "snapshot_count" so rename the
variable to "snap_count".
The lv_layout and lv_type fields together help with LV identification.
We can do basic identification using the lv_attr field which provides
very condensed view. In contrast to that, the new lv_layout and lv_type
fields provide more detialed information on exact layout and type used
for LVs.
For top-level LVs which are pure types not combined with any
other LV types, the lv_layout value is equal to lv_type value.
For non-top-level LVs which may be combined with other types,
the lv_layout describes the underlying layout used, while the
lv_type describes the use/type/usage of the LV.
These two new fields are both string lists so selection (-S/--select)
criteria can be defined using the list operators easily:
[] for strict matching
{} for subset matching.
For example, let's consider this:
$ lvs -a -o name,vg_name,lv_attr,layout,type
LV VG Attr Layout Type
[lvol1_pmspare] vg ewi------- linear metadata,pool,spare
pool vg twi-a-tz-- pool,thin pool,thin
[pool_tdata] vg rwi-aor--- level10,raid data,pool,thin
[pool_tdata_rimage_0] vg iwi-aor--- linear image,raid
[pool_tdata_rimage_1] vg iwi-aor--- linear image,raid
[pool_tdata_rimage_2] vg iwi-aor--- linear image,raid
[pool_tdata_rimage_3] vg iwi-aor--- linear image,raid
[pool_tdata_rmeta_0] vg ewi-aor--- linear metadata,raid
[pool_tdata_rmeta_1] vg ewi-aor--- linear metadata,raid
[pool_tdata_rmeta_2] vg ewi-aor--- linear metadata,raid
[pool_tdata_rmeta_3] vg ewi-aor--- linear metadata,raid
[pool_tmeta] vg ewi-aor--- level1,raid metadata,pool,thin
[pool_tmeta_rimage_0] vg iwi-aor--- linear image,raid
[pool_tmeta_rimage_1] vg iwi-aor--- linear image,raid
[pool_tmeta_rmeta_0] vg ewi-aor--- linear metadata,raid
[pool_tmeta_rmeta_1] vg ewi-aor--- linear metadata,raid
thin_snap1 vg Vwi---tz-k thin snapshot,thin
thin_snap2 vg Vwi---tz-k thin snapshot,thin
thin_vol1 vg Vwi-a-tz-- thin thin
thin_vol2 vg Vwi-a-tz-- thin multiple,origin,thin
Which is a situation with thin pool, thin volumes and thin snapshots.
We can see internal 'pool_tdata' volume that makes up thin pool has
actually a level10 raid layout and the internal 'pool_tmeta' has
level1 raid layout. Also, we can see that 'thin_snap1' and 'thin_snap2'
are both thin snapshots while 'thin_vol1' is thin origin (having
multiple snapshots).
Such reporting scheme provides much better base for selection criteria
in addition to providing more detailed information, for example:
$ lvs -a -o name,vg_name,lv_attr,layout,type -S 'type=metadata'
LV VG Attr Layout Type
[lvol1_pmspare] vg ewi------- linear metadata,pool,spare
[pool_tdata_rmeta_0] vg ewi-aor--- linear metadata,raid
[pool_tdata_rmeta_1] vg ewi-aor--- linear metadata,raid
[pool_tdata_rmeta_2] vg ewi-aor--- linear metadata,raid
[pool_tdata_rmeta_3] vg ewi-aor--- linear metadata,raid
[pool_tmeta] vg ewi-aor--- level1,raid metadata,pool,thin
[pool_tmeta_rmeta_0] vg ewi-aor--- linear metadata,raid
[pool_tmeta_rmeta_1] vg ewi-aor--- linear metadata,raid
(selected all LVs which are related to metadata of any type)
lvs -a -o name,vg_name,lv_attr,layout,type -S 'type={metadata,thin}'
LV VG Attr Layout Type
[pool_tmeta] vg ewi-aor--- level1,raid metadata,pool,thin
(selected all LVs which hold metadata related to thin)
lvs -a -o name,vg_name,lv_attr,layout,type -S 'type={thin,snapshot}'
LV VG Attr Layout Type
thin_snap1 vg Vwi---tz-k thin snapshot,thin
thin_snap2 vg Vwi---tz-k thin snapshot,thin
(selected all LVs which are thin snapshots)
lvs -a -o name,vg_name,lv_attr,layout,type -S 'layout=raid'
LV VG Attr Layout Type
[pool_tdata] vg rwi-aor--- level10,raid data,pool,thin
[pool_tmeta] vg ewi-aor--- level1,raid metadata,pool,thin
(selected all LVs with raid layout, any raid layout)
lvs -a -o name,vg_name,lv_attr,layout,type -S 'layout={raid,level1}'
LV VG Attr Layout Type
[pool_tmeta] vg ewi-aor--- level1,raid metadata,pool,thin
(selected all LVs with raid level1 layout exactly)
And so on...
_pvcreate_check() has two missing requirements:
After refreshing filters there must be a rescan.
(Otherwise the persistent filter may remain empty.)
After wiping a signature, the filters must be refreshed.
(A device that was previously excluded by the filter due to
its signature might now need to be included.)
If several devices are added at once, the repeated scanning isn't
strictly needed, but we can address that later as part of the command
processing restructuring (by grouping the devices).
Replace the new pvcreate code added by commit
54685c20fc "filters: fix regression caused
by commit e80884cd080cad7e10be4588e3493b9000649426"
with this change to _pvcreate_check().
The filter refresh problem dates back to commit
acb4b5e4de "Fix pvcreate device check."
The message "Cannot deactivate remotely exclusive device locally." makes
sense only for clustered LV. If the LV is non-clustered, then it's
always exclusive by definition and if it's already deactivated, this
message pops up inappropriately as those two conditions are met.
So issue the message only if the conditions are met AND we have clustered VG.
Commit e80884cd08 tried to dump filters
for them to be reevaluated when creating a PV to avoid overwriting
any existing signature that may have been created after last
scan/filtering.
However, we need to call refresh_filters instead of
persistent_filter->dump since dump requires proper rescannig to fill
up the persistent filter again. However, this is true only for pvcreate
but not for vgcreate with PV creation where the scanning happens before
this PV creation and hence the next rescan (if not full scan), does not
fill the persistent filter.
Also, move refresh_filters so that it's called sooner and only for
pvcreate, vgcreate already calls lvmcache_label_scan(cmd, 2) which
then calls refresh_filters itself, so no need to reevaluate this again.
This caused the persistent filter (/etc/lvm/cache/.cache file) to be
wrong and contain only the PV just being processed with
vgcreate <vg_name> <pv_name_to_create>.
This regression caused other block devices to be filtered out in case
the vgcreate with PV creation was used and then the persistent filter
is used by any other LVM command afterwards.
Make lvresize -l+%FREE support approximate allocation.
Move existing "Reducing/Extending' message to verbose level
and change it to say 'up to' if approximate allocation is being used.
Replace it with a new message that gives the actual old and new size or
says 'unchanged'.
This is addendum to commit 2e82a070f3
which fixed these spurious messages that appeared after commit
651d5093ed ("avoid pv_read in
find_pv_by_name").
There was one more "not found" message issued in case the device
could not be found in device cache (commit 2e82a07 fixed this only
for PV lookup itself). But if we "allow_unformatted" for
find_pv_by_name, we should not issue this message even in case
the device can't be found in dev cache as we just need to know
whether there's a PV or not for the code to decide on next steps
and we don't want to issue any messages if either device itself
is not found or PV is not found.
For example, when we were creating a new PV (and so allow_unformatted = 1)
and the device had a signature on it which caused it to be filtered
by device filter (e.g. MD signature if md filtering is enabled),
or it was part of some other subsystem (e.g. multipath), this message
was issued on find_pv_by_name call which was misleading.
Also, remove misleading "stack" call in case find_pv_by_name
returns NULL in pvcreate_check - any error state is reported
later by pvcreate_check code so no need to "stack" here.
There's one more and proper check to issue "not found" message if
the device can't be found in device cache within pvcreate_check fn
so this situation is still covered properly later in the code.
Before this patch (/dev/sda contains MD signature and is therefore filtered):
$ pvcreate /dev/sda
Physical volume /dev/sda not found
WARNING: linux_raid_member signature detected on /dev/sda at offset 4096. Wipe it? [y/n]:
With this patch applied:
$ pvcreate /dev/sda
WARNING: linux_raid_member signature detected on /dev/sda at offset 4096. Wipe it? [y/n]:
Non-existent devices are still caught properly:
$ pvcreate /dev/sdx
Device /dev/sdx not found (or ignored by filtering).
Fix get_pool_params to only read params.
Add poolmetadataspare option to get_pool_params.
Move all profile code into update_pool_params.
Move recalculate code into pool_manip.c
Cache pools are similar as with thin pools.
Add (needs %s) - since cache has currently
a bit strange need for extra few kb over
our default 4M extent size so make it more obvious.
This is addendum for commit 6dc7b783c8.
LVM1 format stores the ALLOCATABLE flag directly in PV header, not
in VG metadata. So the code needs to be fixed further to work
properly for lvm1 format so that the correct PV header is written
(the flag is set only if the PV is in some VG, unset otherwise).
Before the patch:
$ lvs -o name,active vg/lvol1 --driverloaded n
WARNING: Activation disabled. No device-mapper interaction will beattempted.
LV Active
lvol1 active
With this patch applied:
$ lvs -o name,active vg/lvol1 --driverloaded n
WARNING: Activation disabled. No device-mapper interaction will be attempted.
LV Active
lvol1 unknown
The same for active_{locally,remotely,exclusively} fields.
Also, rename headings for these fields (ActLocal/ActRemote/ActExcl).
The get_lv_type_name helps with translating volume type
to human readable form (can be used in reports or
various messages if needed).
The lv_is_linear and lv_is_striped complete the set of
lv_is_* functions that identify exact volume types.
Mention parent LV as well as the LV triggering the warning.
Still leaves some confusing cases but its not worth fixing them
at the moment.
(Thin pool inactive but a thin volume active => deactivate thin vol.
Inactive mirror/raid with pvmove in progress => complete pvmove and
active&deactivate mirror/raid.
If new VG already exists it requires some LVs to be inactive
unnecessarily.)
Support remove of thin volumes With --force --force
when thin pools is damaged.
This way it's possible to remove thin pool with
unrepairable metadata without requiring to
manually edit lvm2 metadata.
lvremove -ff vg/pool
removes all thin volumes and pool even when
thin pool cannot be activated (to accept
removal of thin volumes in kernel metadata)
Since vg_name inside /lib function has already been ignored mostly
except for a few debug prints - make it and official internal API
feature.
vg_name is used only in /tools while the VG is not yet openned,
and when lvresize/lvcreate /lib function is called with VG pointer
already being used, then vg_name becomes irrelevant (it's not been
validated anyway).
So any internal user of lvcreate_params and lvresize_params does not
need to set vg_name pointer and may leave it NULL.
When creating pool's metadata - create initial LV for clearing with some
generic name and after the volume is create & cleared - rename it to
reserved name '_tmeta/_cmeta'.
We should not expose 'reserved' names for public LVs.
When repairing RAID LVs that have multiple PVs per image, allow
replacement images to be reallocated from the PVs that have not
failed in the image if there is sufficient space.
This allows for scenarios where a 2-way RAID1 is spread across 4 PVs,
where each image lives on two PVs but doesn't use the entire space
on any of them. If one PV fails and there is sufficient space on the
remaining PV in the image, the image can be reallocated on just the
remaining PV.
Previously, the seg_pvs used to track free and allocated space where left
in place after 'release_pv_segment' was called to free space from an LV.
Now, an attempt is made to combine any adjacent seg_pvs that also track
free space. Usually, this doesn't provide much benefit, but in a case
where one command might free some space and then do an allocation, it
can make a difference. One such case is during a repair of a RAID LV,
where one PV of a multi-PV image fails. This new behavior is used when
the replacement image can be allocated from the remaining space of the
PV that did not fail. (First the entire image with the failed PV is
removed. Then the image is reallocated from the remaining PVs.)
I've changed build_parallel_areas_from_lv to take a new parameter
that allows the caller to build parallel areas by LV vs by segment.
Previously, the function created a list of parallel areas for each
segment in the given LV. When it came time for allocation, the
parallel areas were honored on a segment basis. This was problematic
for RAID because any new RAID image must avoid being placed on any
PVs used by other images in the RAID. For example, if we have a
linear LV that has half its space on one PV and half on another, we
do not want an up-convert to use either of those PVs. It should
especially not wind up with the following, where the first portion
of one LV is paired up with the second portion of the other:
------PV1------- ------PV2-------
[ 2of2 image_1 ] [ 1of2 image_1 ]
[ 1of2 image_0 ] [ 2of2 image_0 ]
---------------- ----------------
Previously, it was possible for this to happen. The change makes
it so that the returned parallel areas list contains one "super"
segment (seg_pvs) with a list of all the PVs from every actual
segment in the given LV and covering the entire logical extent range.
This change allows RAID conversions to function properly when there
are existing images that contain multiple segments that span more
than one PV.
...to avoid using cached value (persistent filter) and therefore
not noticing any change made after last scan/filtering - the state
of the device may have changed, for example new signatures added.
$ lvm dumpconfig --type diff
allocation {
use_blkid_wiping=0
}
devices {
obtain_device_list_from_udev=0
}
$ cat /etc/lvm/cache/.cache | grep sda
$ vgscan
Reading all physical volumes. This may take a while...
Found volume group "fedora" using metadata type lvm2
$ cat /etc/lvm/cache/.cache | grep sda
"/dev/sda",
$ parted /dev/sda mklabel gpt
Information: You may need to update /etc/fstab.
$ parted /dev/sda print
Model: QEMU QEMU HARDDISK (scsi)
Disk /dev/sda: 134MB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags:
Number Start End Size File system Name Flags
$ cat /etc/lvm/cache/.cache | grep sda
"/dev/sda",
====
Before this patch:
$ pvcreate /dev/sda
Physical volume "/dev/sda" successfully created
With this patch applied:
$ pvcreate /dev/sda
Physical volume /dev/sda not found
Device /dev/sda not found (or ignored by filtering).
'lvs' would segfault if trying to display the "move pv" if the
pvmove was run with '--atomic'. The structure of an atomic pvmove
is different and requires us to descend another level in the
LV tree to retrieve the PV information.
In 'find_pvmove_lv', separate the code that searches the atomic
pvmove LVs from the code that searches the normal pvmove LVs. This
cleans up the segment iterator code a bit.
pvmove can be used to move single LVs by name or multiple LVs that
lie within the specified PV range (e.g. /dev/sdb1:0-1000). When
moving more than one LV, the portions of those LVs that are in the
range to be moved are added to a new temporary pvmove LV. The LVs
then point to the range in the pvmove LV, rather than the PV
range.
Example 1:
We have two LVs in this example. After they were
created, the first LV was grown, yeilding two segments
in LV1. So, there are two LVs with a total of three
segments.
Before pvmove:
--------- --------- ---------
| LV1s0 | | LV2s0 | | LV1s1 |
--------- --------- ---------
| | |
-------------------------------------
PV | 000 - 255 | 256 - 511 | 512 - 767 |
-------------------------------------
After pvmove inserts the temporary pvmove LV:
--------- --------- ---------
| LV1s0 | | LV2s0 | | LV1s1 |
--------- --------- ---------
| | |
-------------------------------------
pvmove0 | seg 0 | seg 1 | seg 2 |
-------------------------------------
| | |
-------------------------------------
PV | 000 - 255 | 256 - 511 | 512 - 767 |
-------------------------------------
Each of the affected LV segments now point to a
range of blocks in the pvmove LV, which purposefully
corresponds to the segments moved from the original
LVs into the temporary pvmove LV.
The current implementation goes on from here to mirror the temporary
pvmove LV by segment. Further, as the pvmove LV is activated, only
one of its segments is actually mirrored (i.e. "moving") at a time.
The rest are either complete or not addressed yet. If the pvmove
is aborted, those segments that are completed will remain on the
destination and those that are not yet addressed or in the process
of moving will stay on the source PV. Thus, it is possible to have
a partially completed move - some LVs (or certain segments of LVs)
on the source PV and some on the destination.
Example 2:
What 'example 1' might look if it was half-way
through the move.
--------- --------- ---------
| LV1s0 | | LV2s0 | | LV1s1 |
--------- --------- ---------
| | |
-------------------------------------
pvmove0 | seg 0 | seg 1 | seg 2 |
-------------------------------------
| | |
| -------------------------
source PV | | 256 - 511 | 512 - 767 |
| -------------------------
| ||
-------------------------
dest PV | 000 - 255 | 256 - 511 |
-------------------------
This update allows the user to specify that they would like the
pvmove mirror created "by LV" rather than "by segment". That is,
the pvmove LV becomes an image in an encapsulating mirror along
with the allocated copy image.
Example 3:
A pvmove that is performed "by LV" rather than "by segment".
--------- ---------
| LV1s0 | | LV2s0 |
--------- ---------
| |
-------------------------
pvmove0 | * LV-level mirror * |
-------------------------
/ \
pvmove_mimage0 / pvmove_mimage1
------------------------- -------------------------
| seg 0 | seg 1 | | seg 0 | seg 1 |
------------------------- -------------------------
| | | |
------------------------- -------------------------
| 000 - 255 | 256 - 511 | | 000 - 255 | 256 - 511 |
------------------------- -------------------------
source PV dest PV
The thing that differentiates a pvmove done in this way and a simple
"up-convert" from linear to mirror is the preservation of the
distinct segments. A normal up-convert would simply allocate the
necessary space with no regard for segment boundaries. The pvmove
operation must preserve the segments because they are the critical
boundary between the segments of the LVs being moved. So, when the
pvmove copy image is allocated, all corresponding segments must be
allocated. The code that merges ajoining segments that are part of
the same LV when the metadata is written must also be avoided in
this case. This method of mirroring is unique enough to warrant its
own definitional macro, MIRROR_BY_SEGMENTED_LV. This joins the two
existing macros: MIRROR_BY_SEG (for original pvmove) and MIRROR_BY_LV
(for user created mirrors).
The advantages of performing pvmove in this way is that all of the
LVs affected can be moved together. It is an all-or-nothing approach
that leaves all LV segments on the source PV if the move is aborted.
Additionally, a mirror log can be used (in the future) to provide tracking
of progress; allowing the copy to continue where it left off in the event
there is a deactivation.
The list of strings is used quite frequently and we'd like to reuse
this simple structure for report selection support too. Make it part
of libdevmapper for general reuse throughout the code.
This also simplifies the LVM code a bit since we don't need to
include and manage lvm-types.h anymore (the string list was the
only structure defined there).
When creating a cache LV with a RAID origin, we need to ensure that
the sub-LVs of that origin properly change their names to include
the "_corig" extention of the top-level LV. We do this by first
performing a 'lv_rename_update' before making the call to
'insert_layer_for_lv'.
- When defining configuration source, the code now uses separate
CONFIG_PROFILE_COMMAND and CONFIG_PROFILE_METADATA markers
(before, it was just CONFIG_PROFILE that did not make the
difference between the two). This helps when checking the
configuration if it contains correct set of options which
are all in either command-profilable or metadata-profilable
group without mixing these groups together - so it's a firm
distinction. The "command profile" can't contain
"metadata profile" and vice versa! This is strictly checked
and if the settings are mixed, such profile is rejected and
it's not used. So in the end, the CONFIG_PROFILE_COMMAND
set of options and CONFIG_PROFILE_METADATA are mutually exclusive
sets.
- Marking configuration with one or the other marker will also
determine the way these configuration sources are positioned
in the configuration cascade which is now:
CONFIG_STRING -> CONFIG_PROFILE_COMMAND -> CONFIG_PROFILE_METADATA -> CONFIG_FILE/CONFIG_MERGED_FILES
- Marking configuration with one or the other marker will also make
it possible to issue a command context refresh (will be probably
a part of a future patch) if needed for settings in global profile
set. For settings in metadata profile set this is impossible since
we can't refresh cmd context in the middle of reading VG/LV metadata
and for each VG/LV separately because each VG/LV can have a different
metadata profile assinged and it's not possible to change these
settings at this level.
- When command profile is incorrect, it's rejected *and also* the
command exits immediately - the profile *must* be correct for the
command that was run with a profile to be executed. Before this
patch, when the profile was found incorrect, there was just the
warning message and the command continued without profile applied.
But it's more correct to exit immediately in this case.
- When metadata profile is incorrect, we reject it during command
runtime (as we know the profile name from metadata and not early
from command line as it is in case of command profiles) and we
*do continue* with the command as we're in the middle of operation.
Also, the metadata profile is applied directly and on the fly on
find_config_tree_* fn call and even if the metadata profile is
found incorrect, we still need to return the non-profiled value
as found in the other configuration provided or default value.
To exit immediately even in this case, we'd need to refactor
existing find_config_tree_* fns so they can return error. Currently,
these fns return only config values (which end up with default
values in the end if the config is not found).
- To check the profile validity before use to be sure it's correct,
one can use :
lvm dumpconfig --commandprofile/--metadataprofile ProfileName --validate
(the --commandprofile/--metadataprofile for dumpconfig will come
as part of the subsequent patch)
- This patch also adds a reference to --commandprofile and
--metadataprofile in the cmd help string (which was missing before
for the --profile for some commands). We do not mention --profile
now as people should use --commandprofile or --metadataprofile
directly. However, the --profile is still supported for backward
compatibility and it's translated as:
--profile == --metadataprofile for lvcreate, vgcreate, lvchange and vgchange
(as these commands are able to attach profile to metadata)
--profile == --commandprofile for all the other commands
(--metadataprofile is not allowed there as it makes no sense)
- This patch also contains some cleanups to make the code handling
the profiles more readable...
When quering for dmeventd monitoring status, check first
if lvm2 is configured to monitor to avoid unwanted start
of dmeventd process for answering monitoring status.
Given a named mirror LV, vgsplit will look for the PVs that compose it
and move them to a new VG. It does this by first looking at the log
and then the legs. If the log is on the same device as one of the mirror
images, a problem occurs. This is because the PV is moved to the new VG
as the log is processed and thus cannot be found in the current VG when
the image is processed. The solution is to check and see if the PV we are
looking for has already been moved to the new VG. If so, it is not an
error.
Perform two allocation attempts with cling if maximise_cling is set,
first with then without positional fill.
Avoid segfaults from confusion between positional and sorted sequential
allocation when number of stripes varies as reported here:
https://www.redhat.com/archives/linux-lvm/2014-March/msg00001.html
Set A_POSITIONAL_FILL if the array of areas is being filled
positionally (with a slot corresponding to each 'leg') rather
than sequentially (with all suitable areas found, to be sorted
and selected from).
When pvmove0 is finished, it replaces temporarily pvmove0
with error segment, however in this case, pvmove0 remains
unremovable in case pvmove --abort is interrupted in this
moment - since it's not a pvmove anymore and normal
lvremove can't be used to remove LOCKED lv.
When down-converting a RAID1 LV, if the user specifies too few devices,
they will get a confusing message.
Ex:
[root]# lvcreate -m 2 --type raid1 -n raid -L 500M taft
Logical volume "raid" created
[root]# lvconvert -m 0 taft/raid /dev/sdd1
Unable to extract enough images to satisfy request
Failed to extract images from taft/raid
This patch makes the error message a bit clearer by telling the user
the count they are trying to remove and the number of devices they
supplied.
[root@bp-01 lvm2]# lvcreate --type raid1 -m 3 -L 200M -n lv vg
Logical volume "lv" created
[root@bp-01 lvm2]# lvconvert -m -3 vg/lv /dev/sdb1
Unable to remove 3 images: Only 1 device given.
Failed to extract images from vg/lv
[root@bp-01 lvm2]# lvconvert -m -3 vg/lv /dev/sd[bc]1
Unable to remove 3 images: Only 2 devices given.
Failed to extract images from vg/lv
[root@bp-01 lvm2]# lvconvert -m -3 vg/lv /dev/sd[bcd]1
[root@bp-01 lvm2]# lvs -a -o name,attr,devices vg
LV Attr Devices
lv -wi-a----- /dev/sde1(1)
This patch doesn't work in all cases. The user can specify the right
number of devices, but not a sufficient amount of devices from the LV.
This will produce the old error message:
[root@bp-01 lvm2]# lvconvert -m -3 vg/lv /dev/sd[bcf]1
Unable to extract enough images to satisfy request
Failed to extract images from vg/lv
However, I think this error message is sufficient for this case.
Since the usability problem were fixed, we can use this function.
Cleanup orphan LVs with TEMPORARY flags
(reduces couple blkid error reports, but couple of them
is still left...)
Since cache segment is purely virtual mapping, it has nothing for
discard. Discardable is cache origin here which is now
properly removed on 'delete' phase.
Plain lv_empty() call needs to only detach cache origin and leave
origin unchanged.
Drop unused passed cmd pointer from function.
TODO:
We have two similar functions (though not identical)
lv_manip.c: for_each_sub_lv()
metadata.c: _lv_each_dependency()
They seem to not always match - we should probably convert
to use only a single function.
Use proper vgmem memory pool for allocation of LV name in the vg
and check if new renamed LV is a valid name.
TODO: validation should really use also VG name, othewise we are not
able to tell "vgname-lvname" will be valid.
Create a separate function to validation snapshot min chunk value
and relocate code into snapshot_manip file.
This function will be shared with lvconvert then.
When we create thin-pool we have used trick to keep
volume active, but since we now support TEMPORARY flag,
we could just localy active & deactive metadata LV,
and let the thinpool through normal activation process.
When pool_has_message() is queried with NULL lv and 0 device_id
it should just return 'true' when there is any message queued.
So it needs to return negative value dm_list_empty().
Since there is no user for this code path in code currently,
this bug has not been triggered.
The same as for allocation/thin_pool_chunk_size - the default value
used is just a starting point. The calculation continues using the
properties of the devices actually used.
The allocation/thin_pool_chunk_size is a bit more complex. It's default
value is evaluated in runtime based on selected thin_pool_chunk_size_policy.
But the value is just a starting point. The calculation then continues
with dependency on the properties of the devices used. Which means for
such a default value, we know only the starting value.
Move flags for segments to segtype header where it seems more closely
related as the features are related to segtype and not activation.
Use unsigned #define - since it's more common in lvm2 source code
for bit flags.
Condition was swapped - however since it's been based on 'random'
memory content it's been missed as attribute has not been set.
So now we have quite a few possible results when testing.
We have old status without separate metadata and
we have kernels with fixed snapshot leak bug.
(in-release update)
Code uses target driver version for better estimation of
max size of COW device for snapshot.
The bug can be tested with this script:
VG=vg1
lvremove -f $VG/origin
set -e
lvcreate -L 2143289344b -n origin $VG
lvcreate -n snap -c 8k -L 2304M -s $VG/origin
dd if=/dev/zero of=/dev/$VG/snap bs=1M count=2044 oflag=direct
The bug happens when these two conditions are met
* origin size is divisible by (chunk_size/16) - so that the last
metadata area is filled completely
* the miscalculated snapshot metadata size is divisible by extent size -
so that there is no padding to extent boundary which would otherwise
save us
Signed-off-by:Mikulas Patocka <mpatocka@redhat.com>
While stripe size is twice the physical extent size,
the original code will not reduce stripe size to maximum
(physical extent size).
Signed-off-by: Zhiqing Zhang <zhangzq.fnst@cn.fujitsu.com>
Start to convert percentage size handling in lvresize to the new
standard. Note in the man pages that this code is incomplete.
Fix a regression in non-percentage allocation in my last check in.
This is what I am aiming for:
-l<extents>
-l<percent> LV/ORIGIN
sets or changes the LV size based on the specified quantity
of logical logical extents (that might be backed by
a higher number of physical extents)
-l<percent> PVS/VG/FREE
sets or changes the LV size so as to allocate or free the
desired quantity of physical extents (that might amount to a
lower number of logical extents for the LV concerned)
-l+50%FREE - Use up half the remaining free space in the VG when
carrying out this operation.
-l50%VG - After this operation, this LV should be using up half the
space in the VG.
-l200%LV - Double the logical size of this LV.
-l+100%LV - Double the logical size of this LV.
-l-50%LV - Reduce the logical size of this LV by half.
Parsing vg structure during supend/commit/resume may require a lot of
memory - so move this into vg_write.
FIXME: there are now multiple cache layers which our doing some thing
multiple times at different levels. Moreover there is now different
caching path with and without lvmetad - this should be unified
and both path should use same mechanism.
Several fixes for the recent changes that treat allocation percentages
as upper limits.
Improve messages to make it easier to see what is happening.
Fix some cases that failed with errors when they didn't need to.
Fix crashes when first_seg() returns NULL.
Remove a couple of log_errors that were actually debugging messages.
Remove 'skip' argument passed into the function.
We always used '0' - as this is the only supported
option (-K) and there is no complementary option.
Also add some testing for behaviour of skipping.
When an origin exists and the 'lvcreate' command is used to create
a cache pool + cache LV, the table is loaded into the kernel but
never instantiated (suspend/resume was never called). A user running
LVM commands would never know that the kernel did not have the
proper state unless they also ran the dmsetup 'table/status' command.
The solution is to suspend/resume the cache LV to make the loaded
tables become active.
Introduce a new parameter called "approx_alloc" that is set when the
desired size of a new LV is specified in percentage terms. If set,
the allocation code tries to get as much space as it can but does not
fail if can at least get some.
One of the practical implications is that users can now specify 100%FREE
when creating RAID LVs, like this:
~> lvcreate --type raid5 -i 2 -l 100%FREE -n lv vg
Users now have the ability to convert their existing logical volumes
into cached logical volumes. A cache pool LV must be specified using
the '--cachepool' argument. The cachepool is the small, fast LV used
to cache the large, slow LV that is being converted.
lv_active_change will enforce proper activation.
Modification of activation was wrong and lead to misuse of
autoactivation. Fix allows to use proper local exclusive activation,
while the removed code turned this into just exclusive
activation (losing required local property).
The libblkid can detect DM_snapshot_cow signature and when creating
new LVs with blkid wiping used (allocation/use_blkid_wiping=1 lvm.conf
setting and --wipe y used at the same time - which it is by default).
Do not issue any prompts about this signature when new LV is created
and just wipe it right away without asking questions. Still keep the
log in verbose mode though.
gcc reports:
metadata/merge.c:229:58: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
metadata/merge.c:232:58: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
This patch allows users to create cache LVs with 'lvcreate'. An origin
or a cache pool LV must be created first. Then, while supplying the
origin or cache pool to the lvcreate command, the cache can be created.
Ex1:
Here the cache pool is created first, followed by the origin which will
be cached.
~> lvcreate --type cache_pool -L 500M -n cachepool vg /dev/small_n_fast
~> lvcreate --type cache -L 1G -n lv vg/cachepool /dev/large_n_slow
Ex2:
Here the origin is created first, followed by the cache pool - allowing
a cache LV to be created covering the origin.
~> lvcreate -L 1G -n lv vg /dev/large_n_slow
~> lvcreate --type cache -L 500M -n cachepool vg/lv /dev/small_n_fast
The code determines which type of LV was supplied (cache pool or origin)
by checking its type. It ensures the right argument was given by ensuring
that the origin is larger than the cache pool.
If the user wants to remove just the cache for an LV. They specify
the LV's associated cache pool when removing:
~> lvremove vg/cachepool
If the user wishes to remove the origin, but leave the cachepool to be
used for another LV, they specify the cache LV.
~> lvremove vg/lv
In order to remove it all, specify both LVs.
This patch also includes tests to create and remove cache pools and
cache LVs.
This patch allows the creation and removal of cache pools. Users are not
yet able to create cache LVs. They are only able to define the space used
for the cache and its characteristics (chunk_size and cache mode ATM) by
creating the cache pool.
A cache LV - from LVM's perpective - is a user accessible device that
links the cachepool LV and the origin LV. The following functions
were added to facilitate the creation and removal of this top-level
LV:
1) 'lv_cache_create' - takes a cachepool and an origin device and links
them into a new top-level LV of 'cache' segment type. No allocation
is necessary in this function, as the sub-LVs contain all of the
necessary allocated space. Only the top-level layer needs to be
created.
2) 'lv_cache_remove' - this function removes the top-level LV of a
cache LV - promoting the cachepool and origin sub-LVs to top-level
devices and leaving them exposed to the user. That is, the
cachepool is unlinked and free to be used with another origin to
form a new cache LV; and the origin is no longer cached.
(Currently, if the cache needs to be flushed, it is done in this
function and the function waits for it to complete before proceeding.
This will be taken out in a future patch in favor of polling.)
