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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.)
Cache pools require a data and metadata area (like thin pools). Unlike
thin pool, if 'cache_pool_metadata_require_separate_pvs' is not set to
'1', the metadata and data area will be allocated from the same device.
It is also done in a manner similar to RAID, where a single chunk of
space is allocated and then split to form the metadata and data device -
ensuring that they are together.
Building on the new DM function that parses DM cache status, we
introduce the following LVM level functions to aquire information
about cache devices:
- lv_cache_block_info: retrieves information on the cache's block/chunk usage
- lv_cache_policy_info: retrieves information on the cache's policy
Avoid use of external origin with size unaligned/incompatible with
thin pool chunk size, since the last chunk is not correctly provisioned
when it is overwritten.
Since we are currently incapable of providing zeroes for
reextended thin volume area, let's disable extension of
such already reduce thin volumes.
(in-release change)
This patch adds the new cachepool segment type - the first of two
necessary to eventually create 'cache' logical volumes. In addition
to the new segment type, updates to makefiles, configure files, the
lv_segment struct, and some necessary libdevmapper flags.
The cachepool is the LV and corresponding segment type that will hold
all information pertinent to the cache itself - it's size, cachemode,
cache policy, core arguments (like migration_threshold), etc.
When thin volume is using external origin, current thin target
is not able to supply 'extended' size with empty pages.
lvm2 detects version and disables extension of LV past the external
origin size in this case.
Thin LV could be however still reduced and extended freely bellow
this size.
In preparation for other segment types that create and use "pools", we
s/create_thin_pool/create_pool/. This way it is not awkward when creating
a cachepool, for example, to use "create_thin_pool".
Functions that handle set-up, tear-down and creation of thin pool
volumes will be more generally applicable when more targets exist
that make use of device-mapper's persistent data format. One of
these targets is the dm-cache target. I've selected some functions
that will be useful for the cache segment type to be moved, since
they will no longer be thin pool specific but are more broadly
useful to any segment type that makes use of a 'pool' LV.
Only flag thin LV for no scanning in udev if this LV is about
to be wiped. This happens only in case the thin LV's pool was not
created with zeroing of the new blocks enabled.
Several fields used to display 0 if undefined. Recent changes
to the way the fields are reported threw away some tests for
valid pointers, leading to segfaults with 'pvs -o all'.
Reinstate the original behaviour.
Introduce FMT_OBSOLETE to identify pool metadata and use it and FMT_MDAS
instead of hard-coded format names.
Explain device accesses on pvscan --cache man page.
When LV is scanned for its dependencies - scan also origin's snapshots,
and thin external origins.
So if any PV from snapshot or external origin device is missing - lvm2 will
avoid trying to activate such device.
Replacement of pv_read by find_pv_by_name in commit
651d5093ed caused spurious
error messages when running pvcreate or vgextend against an
unformatted device.
Physical volume /dev/loop4 not found
Physical volume "/dev/loop4" successfully created
Physical volume /dev/loop4 not found
Physical volume /dev/loop4 not found
Physical volume "/dev/loop4" successfully created
Volume group "vg1" successfully extended
If we're calling pvcreate on a device that already has a PV label,
the blkid detects the existing PV and then we consider it for wiping
before we continue creating the new PV label and we issue a warning
with a prompt whether such old PV label should be removed. We don't
do this with native signature detection code. Let's make it consistent
with old behaviour.
But still keep this "PV" (identified as "LVM1_member" or "LVM2_member"
by blkid) detection when creating new LVs to avoid unexpected PV label
appeareance inside LV.
Optimize and cleanup recently introduced new function wipe_lv.
Use compound literals to get nicely initialized wipe_params struct.
Pass in lv as explicit argument for wipe_lv.
Use cmd from lv structure.
Initialize only non-null members so it's easy to see what
is the special arg.
Drop find_merging_snapshot() function. Use find_snapshot()
called after check for lv_is_merging_origin() which
is the commonly used code path - so we avoid duplicated
tests and potential risk of derefering NULL point
in unhandled error path.
This is actually the wipefs functionailty as a matter of fact
(wipefs uses the same libblkid calls).
libblkid is more rich when it comes to detecting various
signatures, including filesystems and users can better
decide what to erase and what should be kept.
The code is shared for both pvcreate (where wiping is necessary
to complete the pvcreate operation) and lvcreate where it's up
to the user to decide.
The verbose output contains a bit more information about the
signature like LABEL and UUID.
For example:
raw/~ # lvcreate -L16m vg
WARNING: linux_raid_member signature detected on /dev/vg/lvol0 at offset 4096. Wipe it? [y/n]
or more verbose one:
raw/~ # lvcreate -L16m vg -v
...
Found existing signature on /dev/vg/lvol0 at offset 4096: LABEL="raw.virt:0" UUID="da6af139-8403-5d06-b8c4-13f6f24b73b1" TYPE="linux_raid_member" USAGE="raid"
WARNING: linux_raid_member signature detected on /dev/vg/lvol0 at offset 4096. Wipe it? [y/n]
The verbose output is the same output as found in blkid.
Use common wipe_lv (former set_lv) fn to do zeroing as well as signature
wiping if needed. Provide new struct wipe_lv_params to define the
functionality.
Bind "lvcreate -W/--wipesignatures y" with proper wipe_lv call.
Also, add "yes" and "force" to lvcreate_params so it's possible
to apply them for the prompt: "WARNING: %s detected on %s. Wipe it? [y/n]".
