During regular VM shutdown, the VM should sync() anyway. (And
admin.vm.volume.Import does fdatasync(), which is also fine.) But let's
be extra careful.
There were (at least) five ways for the volume's nominal size and the
volume image file's actual size to desynchronize:
- loading a stale qubes.xml if a crash happened right after resizing the
image but before saving the updated qubes.xml (-> previously fixed)
- restarting a snap_on_start volume after resizing the volume or its
source volume (-> previously fixed)
- reverting to a differently sized revision
- importing a volume
- user tinkering with image files
Rather than trying to fix these one by one and hoping that there aren't
any others, override the volume size getter itself to always update from
the image file size. (If the getter is called though the storage API, it
takes the volume lock to avoid clobbering the nominal size when resize()
is running concurrently.)
And change the volume lock from an asyncio.Lock to a threading.Lock -
locking is now handled before coroutinization.
This will allow the coroutinized resize() and a new *not* coroutinized
size() getter from one of the next commits ("storage/reflink: preferably
get volume size from image size") to both run under the volume lock.
Successfully resize volumes without any currently existing image file,
e.g. cleanly stopped volatile volumes: Just update the nominal size in
this case.
Convert create(), verify(), remove(), start(), stop(), revert(),
resize(), and import_volume() into coroutine methods, via a decorator
that runs them in the event loop's thread-based default executor.
This reduces UI hangs by unblocking the event loop, and can e.g. speed
up VM starts by starting multiple volumes in parallel.
Instead of raising a NotImplementedError, just return self like 'file'
and lvm_thin. This is needed when Storage.clone() is modified in another
commit* to no longer swallow exceptions.
* "storage: factor out _wait_and_reraise(); fix clone/create"
Import volume data to a new _path_import (instead of _path_dirty) before
committing to _path_clean. In case the computer crashes while an import
operation is running, the partially written file should not be attached
to Xen on the next volume startup.
Use <name>-import.img as the filename like 'file' does, to be compatible
with qubes.tests.api_admin/TC_00_VMs/test_510_vm_volume_import.
When the AT_REPLACE flag for linkat() finally lands in the Linux kernel,
_replace_file() can be modified to use unnamed (O_TMPFILE) tempfiles.
Until then, make sure stale tempfiles from previous crashes can't hang
around for too long.
It's sort of useful to be able to revert a volume that has only ever
been started once to its empty state. And the lvm_thin driver allows it
too, so why not.
Don't rely on timestamps to sort revisions - the clock can go backwards
due to time sync. Instead, use a monotonically increasing natural number
as the revision ID.
Old revision example: private.img@2018-01-02-03T04:05:06Z (ignored now)
New revision example: private.img.123@2018-01-02-03T04:05:06Z
* storage-properties:
storage: use None for size/usage properties if unknown
tests: call search_pool_containing_dir with various dirs and pools
storage: make DirectoryThinPool helper less verbose, add sudo
api/admin: add 'included_in' to admin.pool.Info call
storage: add Pool.included_in() method for checking nested pools
storage: move and generalize RootThinPool helper class
storage/kernels: refuse changes to 'rw' and 'revisions_to_keep'
api/admin: implement admin.vm.volume.Set.rw method
api/admin: include 'revisions_to_keep' and 'is_outdated' in volume info
It may happen that one pool is inside a volume of other pool. This is
the case for example for varlibqubes pool (file driver,
dir_path=/var/lib/qubes) and default lvm pool (lvm_thin driver). The
latter include whole root filesystem, so /var/lib/qubes too.
This is relevant for proper disk space calculation - to not count some
space twice.
QubesOS/qubes-issues#3240QubesOS/qubes-issues#3241
This adds the file-reflink storage driver. It is never selected
automatically for pool creation, especially not the creation of
'varlibqubes' (though it can be used if set up manually).
The code is quite small:
reflink.py lvm.py file.py + block-snapshot
sloccount 334 lines 447 (134%) 570 (171%)
Background: btrfs and XFS (but not yet ZFS) support instant copies of
individual files through the 'FICLONE' ioctl behind 'cp --reflink'.
Which file-reflink uses to snapshot VM image files without an extra
device-mapper layer. All the snapshots are essentially freestanding;
there's no functional origin vs. snapshot distinction.
In contrast to 'file'-on-btrfs, file-reflink inherently avoids
CoW-on-CoW. Which is a bigger issue now on R4.0, where even AppVMs'
private volumes are CoW. (And turning off the lower, filesystem-level
CoW for 'file'-on-btrfs images would turn off data checksums too, i.e.
protection against bit rot.)
Also in contrast to 'file', all storage features are supported,
including
- any number of revisions_to_keep
- volume.revert()
- volume.is_outdated
- online fstrim/discard
Example tree of a file-reflink pool - *-dirty.img are connected to Xen:
- /var/lib/testpool/appvms/foo/volatile-dirty.img
- /var/lib/testpool/appvms/foo/root-dirty.img
- /var/lib/testpool/appvms/foo/root.img
- /var/lib/testpool/appvms/foo/private-dirty.img
- /var/lib/testpool/appvms/foo/private.img
- /var/lib/testpool/appvms/foo/private.img@2018-01-02T03:04:05Z
- /var/lib/testpool/appvms/foo/private.img@2018-01-02T04:05:06Z
- /var/lib/testpool/appvms/foo/private.img@2018-01-02T05:06:07Z
- /var/lib/testpool/appvms/bar/...
- /var/lib/testpool/appvms/...
- /var/lib/testpool/template-vms/fedora-26/...
- /var/lib/testpool/template-vms/...
It looks similar to a 'file' pool tree, and in fact file-reflink is
drop-in compatible:
$ qvm-shutdown --all --wait
$ systemctl stop qubesd
$ sed 's/ driver="file"/ driver="file-reflink"/g' -i.bak /var/lib/qubes/qubes.xml
$ systemctl start qubesd
$ sudo rm -f /path/to/pool/*/*/*-cow.img*
If the user tries to create a fresh file-reflink pool on a filesystem
that doesn't support reflinks, qvm-pool will abort and mention the
'setup_check=no' option. Which can be passed to force a fallback on
regular sparse copies, with of course lots of time/space overhead. The
same fallback code is also used when initially cloning a VM from a
foreign pool, or from another file-reflink pool on a different
mountpoint.
'journalctl -fu qubesd' will show all file-reflink copy/rename/remove
operations on VM creation/startup/shutdown/etc.
