Fix mount-tests readiness detection on Unix and add FUSE diagnostics

Author: tbdye

.github/workflows/ci.yml

@@ -199,13 +199,29 @@ jobs:
       - name: Verify FUSE backend
         run: |
           python -c "
+          import sys, os
           try:
               from fuse import FUSE
               print('fusepy: OK (FUSE class imported)')
           except EnvironmentError as e:
               print(f'fusepy: FUSE backend not found: {e}')
+              sys.exit(0)
           except ImportError:
               print('fusepy: not installed')
+              sys.exit(0)
+          # Verify /dev/fuse accessible on Linux
+          if sys.platform.startswith('linux'):
+              if os.path.exists('/dev/fuse'):
+                  mode = oct(os.stat('/dev/fuse').st_mode)
+                  print(f'/dev/fuse exists, mode={mode}')
+                  try:
+                      fd = os.open('/dev/fuse', os.O_RDWR)
+                      os.close(fd)
+                      print('/dev/fuse: read-write access OK')
+                  except PermissionError as e:
+                      print(f'/dev/fuse: access denied: {e}')
+              else:
+                  print('/dev/fuse: NOT FOUND')
           "
         continue-on-error: true
 

tests/integration/conftest.py

@@ -211,6 +211,11 @@ def _mount(image, driver=None, extra_args=None, timeout=_MOUNT_TIMEOUT):
             ),
         )
 
+        # Cache parent device ID for Unix mount detection (st_dev changes
+        # when FUSE attaches).
+        if not sys.platform.startswith("win"):
+            parent_dev = os.stat(os.path.dirname(str(mountpoint))).st_dev
+
         # Poll until mount is detected or timeout
         deadline = time.monotonic() + timeout
         mounted = False
@@ -223,24 +228,37 @@ def _mount(image, driver=None, extra_args=None, timeout=_MOUNT_TIMEOUT):
                     f"Mount process exited early (rc={proc.returncode}).\n"
                     f"stdout: {stdout}\nstderr: {stderr}"
                 )
-            # On Windows, ismount detects the drive letter before the
-            # filesystem is fully initialized. Use listdir as the
-            # authoritative readiness check on all platforms.
+            # Platform-aware readiness detection:
+            # - Windows: drive letter doesn't exist until WinFSP creates it,
+            #   so listdir not throwing means the mount appeared.
+            # - Unix: mountpoint directory already exists, so listdir would
+            #   succeed immediately. Instead check st_dev -- FUSE attaches a
+            #   new device, so st_dev will differ from the parent directory.
             try:
-                os.listdir(str(mountpoint))
+                if sys.platform.startswith("win"):
+                    os.listdir(str(mountpoint))
+                else:
+                    if os.stat(str(mountpoint)).st_dev != parent_dev:
+                        mounted = True
+                        break
+                    else:
+                        time.sleep(_MOUNT_POLL_INTERVAL)
+                        continue
                 mounted = True
                 break
             except OSError:
                 pass
             time.sleep(_MOUNT_POLL_INTERVAL)
 
         if not mounted:
-            # Clean up the failed mount attempt
+            # Clean up the failed mount attempt and capture diagnostics
             proc.kill()
             proc.wait(timeout=_PROCESS_KILL_TIMEOUT)
+            stdout = proc.stdout.read().decode(errors="replace")
+            stderr = proc.stderr.read().decode(errors="replace")
             raise RuntimeError(
-                f"Mount not detected at {mountpoint} within {timeout}s. "
-                f"Process still running: {proc.poll() is None}"
+                f"Mount not detected at {mountpoint} within {timeout}s.\n"
+                f"stdout: {stdout}\nstderr: {stderr}"
             )
 
         _active_mounts.append((proc, mountpoint))