storage: limit data written per VDI with --write-volume-cap

Refactor stream management to support arbitrary span distributions.
The new StreamSpan dataclass encapsulates stream metadata and operations,
while partially_populate_device() now supports configurable span counts
and skip patterns.

This required to upgrade randstream to the version 0.6.0 which supports
arbitrary position.
 
The default cap is 2GiB.

Signed-off-by: Gaëtan Lehmann <gaetan.lehmann@vates.tech>

Author: glehmann

conftest.py

@@ -110,6 +110,12 @@ def pytest_addoption(parser: pytest.Parser) -> None:
         default="1GiB",
         help="Default volume size for tests"
     )
+    parser.addoption(
+        "--write-volume-cap",
+        action="store",
+        default="2GiB",
+        help="Maximum amount of data written to a volume"
+    )
 
 def pytest_configure(config: pytest.Config) -> None:
     global_config.ignore_ssh_banner = config.getoption('--ignore-ssh-banner')
@@ -119,6 +125,9 @@ def pytest_configure(config: pytest.Config) -> None:
     volume_size = config.getoption('--volume-size')
     assert volume_size is not None
     global_config.volume_size = parse_size(volume_size)
+    write_volume_cap = config.getoption('--write-volume-cap')
+    assert write_volume_cap is not None
+    global_config.write_volume_cap = parse_size(write_volume_cap)
 
 def pytest_generate_tests(metafunc: pytest.Metafunc) -> None:
     if "vm_ref" in metafunc.fixturenames:

lib/config.py

@@ -3,6 +3,7 @@
 ignore_ssh_banner = False
 ssh_output_max_lines = 20
 volume_size = 1 * GiB
+write_volume_cap = 2 * GiB
 
 def sr_device_config(datakey: str, *, required: list[str] = []) -> dict[str, str]:
     import data  # import here to avoid depending on this user file for collecting tests

tests/storage/nfs/test_nfs_sr.py

@@ -140,17 +140,17 @@ def test_invalid_vdi_size(self, nfs_sr: SR, image_format: ImageFormat):
     @pytest.mark.usefixtures('vm_ref')
     @pytest.mark.parametrize('dispatch_nfs', ['vm_on_nfs_sr', 'vm_on_nfs4_sr'], indirect=True)
     @pytest.mark.parametrize("compression", ["none", "gzip", "zstd"])
-    def test_xva_export_import(self, dispatch_nfs: VM, compression: XVACompression, temp_large_dir: str, defer: Defer) \
-            -> None:
-        if "NFS4" in dispatch_nfs.vdis[0].sr.get_name_label() and config.volume_size > 20 * GiB:
+    def test_xva_export_import(self, dispatch_nfs: VM, compression: XVACompression, temp_large_dir: str,
+                               defer: Defer) -> None:
+        if "NFS4" in dispatch_nfs.vdis[0].sr.get_name_label() and config.write_volume_cap > 20 * GiB:
             pytest.skip("Skipping NFSv4 large VDI test (known performance issue)")
         xva_export_import(dispatch_nfs, compression, temp_large_dir, defer)
 
     @pytest.mark.small_vm
     @pytest.mark.parametrize('dispatch_nfs', ['nfs_sr', 'nfs4_sr'], indirect=True)
     def test_vdi_export_import(self, storage_test_vm: VM, dispatch_nfs: SR, image_format: ImageFormat,
                                temp_large_dir: str, defer: Defer) -> None:
-        if "NFS4" in dispatch_nfs.get_name_label() and config.volume_size > 20 * GiB:
+        if "NFS4" in dispatch_nfs.get_name_label() and config.write_volume_cap > 20 * GiB:
             pytest.skip("Skipping NFSv4 large VDI test (known performance issue)")
         vdi_export_import(storage_test_vm, dispatch_nfs, image_format, temp_large_dir, defer)