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fix(instances): a snapshot needs free space in the VM's storage pools

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A disk-only snapshot was taken without any space check, though its
overlays grow as the guest writes and a later delete merges them down;
a full pool pauses the guest and can leave the snapshot undeletable.
Only a memory snapshot was checked, for the memory alone.

Before a snapshot, each storage pool with a disk of the VM must have
free a share of those disks' virtual size (10%, at least 1 GiB), and
the pool of the memory file the VM's memory on top. Both values are on
the Settings page (Snapshot Free Percent, Snapshot Free Min GiB; 0
turns a rule off, an invalid value keeps the default). The pools are
refreshed first, and a failed refresh or an unreadable volume refuses
the snapshot instead of skipping the check; a disk in no pool is not
checked. Nothing is reserved: later writes can still fill a pool.
This commit is contained in:
catborise 2026-10-13 11:47:40 +03:00
parent f766890825
commit 5f8f7a8643
8 changed files with 227 additions and 30 deletions
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62
vrtManager/instance.py
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@ -1576,12 +1576,14 @@ class wvmInstance(wvmConnect):
</domainsnapshot>"""
self._snapshotCreateXML(xml, 0)
def create_external_snapshot(self, name, desc="", memory=False, quiesce=False):
def create_external_snapshot(self, name, desc="", memory=False, quiesce=False, free_percent=10, free_min_gib=1):
"""A disk-only snapshot, or with memory too (running VMs only). Every
disk gets a libvirt-named overlay next to it; the memory file goes
next to the first disk. quiesce: the guest agent freezes the guest's
file systems for a disk-only snapshot of a running VM (libvirt
accepts it only without memory, which keeps the whole state anyway)."""
accepts it only without memory, which keeps the whole state anyway).
free_percent, free_min_gib: the free space each pool keeps (see
_check_snapshot_space)."""
if not SNAPSHOT_NAME.fullmatch(name):
raise util.OperationError(
"Snapshot names are 1-64 letters, digits, '.', '_' or '-' and do not start with '.'"
@ -1612,7 +1614,17 @@ class wvmInstance(wvmConnect):
raise util.OperationError(f"Eject the media from {dev} first")
elif disk.get("type") != "file":
raise util.OperationError(f"Disk {dev} is not a file; external snapshots need file disks")
memory_xml = self._snapshot_memory_xml(name, tree) if memory else ""
disks = list(self._disk_sources(tree).values())
# free space, and the top overlays, are known to the pools only after
# a refresh; nothing has changed yet when it fails
try:
self.refresh_instance_pools()
except libvirtError as err:
raise util.OperationError(
f"The storage pools could not be refreshed, so their free space is unknown: {err}"
) from None
memory_xml, memory_pool = self._snapshot_memory(name, disks) if memory else ("", None)
self._check_snapshot_space(disks, memory_pool, free_percent, free_min_gib)
xml = (
f"<domainsnapshot><name>{name}</name>"
f"<description>{util.xml_escape(desc)}</description>{memory_xml}</domainsnapshot>"
@ -1625,24 +1637,50 @@ class wvmInstance(wvmConnect):
self._snapshotCreateXML(xml, flags)
self._refresh_pools_after_snapshot()
def _snapshot_memory_xml(self, name, tree):
"""The <memory> element of a snapshot that saves memory: a file in the
storage pool of the first disk, which must have room for it."""
def _snapshot_memory(self, name, disks):
"""The <memory> element of a snapshot that saves memory, and the
storage pool its file goes into: the pool of the first disk."""
if self.get_status() != 1:
raise util.OperationError("Memory is saved only from a running VM")
disks = list(self._disk_sources(tree).values())
if not disks:
raise util.OperationError("The VM has no disk to keep its memory next to")
# the top overlay is known to its pool only after a refresh
self.refresh_instance_pools()
try:
pool = self.get_volume_by_path(disks[0]).storagePoolLookupByVolume()
except libvirtError:
raise util.OperationError(f"{disks[0]} is not in a storage pool; memory is saved only into one") from None
if pool.info()[3] < self.get_cur_memory() * 1024 * 1024:
raise util.OperationError(f"Storage pool {pool.name()} has less free space than the VM's memory")
path = os.path.join(os.path.dirname(disks[0]), f"{self.get_uuid()}.{name}.mem")
return f"<memory snapshot='external' file='{util.xml_escape(path)}'/>"
return f"<memory snapshot='external' file='{util.xml_escape(path)}'/>", pool.name()
def _check_snapshot_space(self, disks, memory_pool, free_percent, free_min_gib):
"""Each storage pool with a disk of the VM keeps free_percent of the
virtual size of those disks free, at least free_min_gib GiB, and the
pool of the memory file the VM's memory on top. The
overlays grow as the guest writes, and a delete merges them down.
This is checked before the snapshot only; nothing is reserved. A
disk in no pool is not checked."""
needed, pools = {}, {}
for path in disks:
try:
vol = self.get_volume_by_path(path)
except libvirtError as err:
if err.get_error_code() != VIR_ERR_NO_STORAGE_VOL:
raise
continue
pool = vol.storagePoolLookupByVolume()
pools[pool.name()] = pool
needed[pool.name()] = needed.get(pool.name(), 0) + vol.info()[1] * free_percent / 100
for name in needed:
needed[name] = max(needed[name], free_min_gib * 1024**3)
if memory_pool:
needed[memory_pool] += self.get_cur_memory() * 1024 * 1024
for name, size in needed.items():
free = pools[name].info()[3]
if free < size:
raise util.OperationError(
f"Storage pool {name} has {free / 1024**3:.1f} GiB free; the snapshot needs {size / 1024**3:.1f} GiB "
f"({free_percent:g}% of the VM's disks in it, at least {free_min_gib:g} GiB, "
"and the memory if it is saved)"
)
def revert_external_snapshot(self, name):
"""libvirt returns the disks and the definition to the snapshot's. A