16720: Add missing import.

[arvados.git] / services / fuse / arvados_fuse / unmount.py

diff --git a/services/fuse/arvados_fuse/unmount.py b/services/fuse/arvados_fuse/unmount.py
index 17ced4b4d08d4916d409495afb6e9f9aacc065d5..dbfea1f90449cb14f3c12df15e6b37001b131bcc 100644 (file)
--- a/services/fuse/arvados_fuse/unmount.py
+++ b/services/fuse/arvados_fuse/unmount.py
@@ -6,6 +6,7 @@ import collections
 import errno
 import os
 import subprocess
+import sys
 import time
 
 
@@ -43,6 +44,41 @@ def paths_to_unmount(path, mnttype):
     return paths
 
 
+def safer_realpath(path, loop=True):
+    """Similar to os.path.realpath(), but avoids calling lstat().
+
+    Leaves some symlinks unresolved."""
+    if path == '/':
+        return path, True
+    elif not path.startswith('/'):
+        path = os.path.abspath(path)
+    while True:
+        path = path.rstrip('/')
+        dirname, basename = os.path.split(path)
+        try:
+            path, resolved = safer_realpath(os.path.join(dirname, os.readlink(path)), loop=False)
+        except OSError as e:
+            # Path is not a symlink (EINVAL), or is unreadable, or
+            # doesn't exist. If the error was EINVAL and dirname can
+            # be resolved, we will have eliminated all symlinks and it
+            # will be safe to call normpath().
+            dirname, resolved = safer_realpath(dirname, loop=loop)
+            path = os.path.join(dirname, basename)
+            if resolved and e.errno == errno.EINVAL:
+                return os.path.normpath(path), True
+            else:
+                return path, False
+        except RuntimeError:
+            if not loop:
+                # Unwind to the point where we first started following
+                # symlinks.
+                raise
+            # Resolving the whole path landed in a symlink cycle, but
+            # we might still be able to resolve dirname.
+            dirname, _ = safer_realpath(dirname, loop=loop)
+            return os.path.join(dirname, basename), False
+
+
 def unmount(path, subtype=None, timeout=10, recursive=False):
     """Unmount the fuse mount at path.
 
@@ -58,6 +94,8 @@ def unmount(path, subtype=None, timeout=10, recursive=False):
     fuse mount at all. Raises an exception if it cannot be unmounted.
     """
 
+    path, _ = safer_realpath(path)
+
     if subtype is None:
         mnttype = None
     elif subtype == '':
@@ -79,6 +117,7 @@ def unmount(path, subtype=None, timeout=10, recursive=False):
 
     was_mounted = False
     attempted = False
+    fusermount_output = b''
     if timeout is None:
         deadline = None
     else:
@@ -118,6 +157,10 @@ def unmount(path, subtype=None, timeout=10, recursive=False):
             return was_mounted
 
         if attempted:
+            # Report buffered stderr from previous call to fusermount,
+            # now that we know it didn't succeed.
+            sys.stderr.write(fusermount_output)
+
             delay = 1
             if deadline:
                 delay = min(delay, deadline - time.time())
@@ -129,12 +172,16 @@ def unmount(path, subtype=None, timeout=10, recursive=False):
             with open('/sys/fs/fuse/connections/{}/abort'.format(m.minor),
                       'w') as f:
                 f.write("1")
-        except OSError as e:
+        except IOError as e:
             if e.errno != errno.ENOENT:
                 raise
 
         attempted = True
         try:
-            subprocess.check_call(["fusermount", "-u", "-z", path])
-        except subprocess.CalledProcessError:
-            pass
+            subprocess.check_output(
+                ["fusermount", "-u", "-z", path],
+                stderr=subprocess.STDOUT)
+        except subprocess.CalledProcessError as e:
+            fusermount_output = e.output
+        else:
+            fusermount_output = b''