openstack/nova
Code Issues Proposed changes

libvirt: Report the allocated size of preallocated file based disks

Browse Source 
At present the Libvirt driver can preallocate file based disks using the
fallocate command and importantly the `-n` option. This option allocates
blocks on the filesystem past the initial EOF of a given file:

```
$ touch test.img ; fallocate -n -l $(( 1024 * 1024 )) test.img
$ ll -lah test.img
-rw-rw-r--. 1 stack stack 0 Apr 16 13:28 test.img
$ du -h test.img
1.0M	test.img
```

This results in a miscalculation of the total disk overcommit for file
based (excluding ploop) disks as os.path.getsize is currently used to
determine the allocated size of these disks:

```
>>> import os
>>> os.path.getsize('test.img')
0
```

Using the above example the disk overcommit would be reported as 1.0M as
the disk appears empty yet will report a potential (virtual) size of 1.0M.

However as the required blocks have already been allocated on the
filesystem the host will report disk_available_least as missing an
additional 1.0M, essentially doubling the allocation for each disk.

To correct this the allocated size of file based (excluding ploop) disks
is reported using `disk_size` from the `qemu-img info` command. This
should ensure blocks allocated past the EOF of the file are taken into
account and correctly reported as allocated.

A future change should ultimately remove the use of the `-n` option with
fallocate, however as this would not help disks that have already been
allocated this has not been included in this change to simplify backports.

Change-Id: If642e51a4e186833349a8e30b04224a3687f5594
Closes-bug: #1764489
This commit is contained in:
Lee Yarwood 2018-04-16 18:08:56 +01:00
parent fb0b785169
commit 23bd8f6263
3 changed files with 39 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

41
nova/tests/unit/virt/libvirt/test_driver.py
View File

@ -4439,8 +4439,9 @@ class LibvirtConnTestCase(test.NoDBTestCase,
@mock.patch.object(dmcrypt, 'delete_volume')
@mock.patch.object(conn._host, '_get_domain', return_value=dom)
def detach_encrypted_volumes(block_device_info, mock_get_domain,
mock_delete_volume):
@mock.patch.object(libvirt_driver.disk_api, 'get_allocated_disk_size')
def detach_encrypted_volumes(block_device_info, mock_get_alloc_size,
mock_get_domain, mock_delete_volume):
conn._detach_encrypted_volumes(instance, block_device_info)
mock_get_domain.assert_called_once_with(instance)
@ -8968,7 +8969,8 @@ class LibvirtConnTestCase(test.NoDBTestCase,
data = objects.LibvirtLiveMigrateData(is_volume_backed=True,
is_shared_instance_path=False)
with test.nested(
mock.patch.object(os.path, 'getsize', mock_getsize),
mock.patch.object(libvirt_driver.disk_api,
'get_allocated_disk_size', mock_getsize),
mock.patch.object(host.Host, '_get_domain', mock_lookup)):
self.assertFalse(drvr._is_shared_block_storage(
instance, data,
@ -11667,9 +11669,14 @@ class LibvirtConnTestCase(test.NoDBTestCase,
fake_libvirt_utils.disk_sizes['/test/disk.local'] = 20 * units.Gi
fake_libvirt_utils.disk_backing_files['/test/disk.local'] = 'file'
self.mox.StubOutWithMock(os.path, "getsize")
os.path.getsize('/test/disk').AndReturn((10737418240))
os.path.getsize('/test/disk.local').AndReturn((3328599655))
self.mox.StubOutWithMock(libvirt_driver.disk_api,
'get_allocated_disk_size')
path = '/test/disk'
size = 10737418240
libvirt_driver.disk_api.get_allocated_disk_size(path).AndReturn((size))
path = '/test/disk.local'
size = 3328599655
libvirt_driver.disk_api.get_allocated_disk_size(path).AndReturn((size))
ret = ("image: /test/disk.local\n"
"file format: qcow2\n"
@ -11819,9 +11826,14 @@ class LibvirtConnTestCase(test.NoDBTestCase,
fake_libvirt_utils.disk_sizes['/test/disk.local'] = 20 * units.Gi
fake_libvirt_utils.disk_backing_files['/test/disk.local'] = 'file'
self.mox.StubOutWithMock(os.path, "getsize")
os.path.getsize('/test/disk').AndReturn((10737418240))
os.path.getsize('/test/disk.local').AndReturn((3328599655))
self.mox.StubOutWithMock(libvirt_driver.disk_api,
'get_allocated_disk_size')
path = '/test/disk'
size = 10737418240
libvirt_driver.disk_api.get_allocated_disk_size(path).AndReturn((size))
path = '/test/disk.local'
size = 3328599655
libvirt_driver.disk_api.get_allocated_disk_size(path).AndReturn((size))
ret = ("image: /test/disk.local\n"
"file format: qcow2\n"
@ -11885,8 +11897,11 @@ class LibvirtConnTestCase(test.NoDBTestCase,
fake_libvirt_utils.disk_sizes['/test/disk'] = 10 * units.Gi
self.mox.StubOutWithMock(os.path, "getsize")
os.path.getsize('/test/disk').AndReturn((10737418240))
self.mox.StubOutWithMock(libvirt_driver.disk_api,
"get_allocated_disk_size")
path = '/test/disk'
size = 10737418240
libvirt_driver.disk_api.get_allocated_disk_size(path).AndReturn((size))
self.mox.ReplayAll()
drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), False)
@ -11895,8 +11910,8 @@ class LibvirtConnTestCase(test.NoDBTestCase,
info = jsonutils.loads(info)
self.assertEqual(1, len(info))
self.assertEqual(info[0]['type'], 'raw')
self.assertEqual(info[0]['path'], '/test/disk')
self.assertEqual(info[0]['disk_size'], 10737418240)
self.assertEqual(info[0]['path'], path)
self.assertEqual(info[0]['disk_size'], size)
self.assertEqual(info[0]['backing_file'], "")
self.assertEqual(info[0]['over_committed_disk_size'], 0)

10
nova/virt/disk/api.py
View File

@ -99,6 +99,16 @@ def get_disk_size(path):
return images.qemu_img_info(path).virtual_size
def get_allocated_disk_size(path):
"""Get the allocated size of a disk image
:param path: Path to the disk image
:returns: Size (in bytes) of the given disk image as allocated on the
filesystem
"""
return images.qemu_img_info(path).disk_size
def extend(image, size):
"""Increase image to size.

2
nova/virt/libvirt/driver.py
View File

@ -7962,7 +7962,7 @@ class LibvirtDriver(driver.ComputeDriver):
fp = os.path.join(dirpath, f)
dk_size += os.path.getsize(fp)
else:
dk_size = int(os.path.getsize(path))
dk_size = disk_api.get_allocated_disk_size(path)
elif disk_type == 'block' and block_device_info:
dk_size = lvm.get_volume_size(path)
else: