Use zpool command to measure ZFS pool sizes accurately

Replace statvfs with zpool list command for ZFS storage pools to get accurate
size and free space metrics. This resolves the 'mountpoint' key error for ZFS
pools and provides more accurate capacity information.

src/pvestorage/__init__.py

@@ -87,15 +87,53 @@ def parse_storage_cfg(file_path='/etc/pve/storage.cfg'):
 
 def get_storage_size(storage):
     try:
-        if storage["type"] in ["dir", "nfs", "cephfs", "zfspool"]:
-            if storage["type"] == "zfspool":
-                path = storage["mountpoint"]
-            else:
-                path = storage["path"]
-            # Get filesystem statistics
+        if storage["type"] == "zfspool":
+            if "pool" not in storage:
+                logging.debug(f"ZFS pool {storage['name']} has no pool name configured")
+                return None
+
+            # Extract the pool name (could be in format like rpool/data)
+            pool_name = storage["pool"].split("/")[0]
+
+            # Use zpool command to get accurate size information
+            import subprocess
+            try:
+                result = subprocess.run(
+                    ["zpool", "list", pool_name, "-p"],
+                    capture_output=True,
+                    text=True,
+                    check=True
+                )
+
+                # Parse the output
+                lines = result.stdout.strip().split("\n")
+                if len(lines) < 2:
+                    logging.warn(f"Unexpected zpool list output format for {pool_name}")
+                    return None
+
+                # Extract values from the second line (the data line)
+                values = lines[1].split()
+                if len(values) < 4:
+                    logging.warn(f"Insufficient data in zpool list output for {pool_name}")
+                    return None
+
+                # Values are: NAME SIZE ALLOC FREE ...
+                # We need the SIZE and FREE values (index 1 and 3)
+                total_size = int(values[1])
+                free_space = int(values[3])
+
+                return {
+                    "total": total_size,
+                    "free": free_space
+                }
+            except (subprocess.SubprocessError, ValueError, IndexError) as e:
+                logging.warn(f"Error running zpool list for {pool_name}: {e}")
+                return None
+
+        elif storage["type"] in ["dir", "nfs", "cephfs"]:
+            # For non-ZFS storage, use statvfs
+            path = storage["path"]
             stats = os.statvfs(path)
-            # Calculate total size and free space in bytes
-            # TODO: find an alternative way to calculate total_size for ZFS
             total_size = stats.f_frsize * stats.f_blocks
             free_space = stats.f_frsize * stats.f_bavail
             return {