wire up the statvfs ldpreload thing in an example test

test_runner/regress/test_disk_usage_eviction.py

@@ -1,4 +1,6 @@
+import json
 import time
+import uuid
 from dataclasses import dataclass
 from pathlib import Path
 from typing import Dict, Iterator, Tuple
@@ -14,6 +16,7 @@ from fixtures.neon_fixtures import (
     RemoteStorageKind,
     wait_for_last_flush_lsn,
     wait_for_upload_queue_empty,
+    wait_until,
 )
 from fixtures.types import Lsn, TenantId, TimelineId
 
@@ -365,3 +368,40 @@ def poor_mans_du(
 
     assert smallest_layer is not None or total_on_disk == 0 and largest_layer == 0
     return (total_on_disk, largest_layer, smallest_layer or 0)
+
+
+def test_disk_usage_eviction_loop_statvfs(eviction_env: EvictionEnv):
+    env = eviction_env
+
+    env.neon_env.pageserver.stop()
+
+    magic = str(uuid.uuid4())
+
+    preload_lib_path: Path = env.neon_env.neon_binpath / "libstatvfs_ldpreload.so"
+    assert preload_lib_path.is_file(), "libstatvfs_ldpreload.so must be built"
+
+    env.neon_env.pageserver.start(
+        overrides=(
+            '--pageserver-config-override=disk_usage_based_eviction={ period = "1s", max_usage_pct = 90, min_avail_bytes = 0 }',
+        ),
+        extra_env_vars={
+            "LD_PRELOAD": str(preload_lib_path.absolute()),
+            "NEON_STATVFS_LDPRELOAD_CONFIG": json.dumps(
+                {
+                    "magic": magic,
+                    "mock": {
+                        "type": "Failure",
+                        "mocked_error": "EIO",
+                    },
+                }
+            ),
+        },
+    )
+
+    def statvfs_called():
+        assert env.neon_env.pageserver.log_contains(".*statvfs_ldpreload status:.*" + magic)
+
+    wait_until(10, 1, statvfs_called)
+
+    assert env.neon_env.pageserver.log_contains(".*statvfs failed.*EIO")
+    env.neon_env.pageserver.allowed_errors.append(".*statvfs failed.*EIO")