X-Git-Url: https://git.arvados.org/arvados.git/blobdiff_plain/2b27132d13fd72f29dbab2297f0d2dc1c110eed1..20a7cf92c668d8d75ca3d1d64f028973a71245d4:/services/fuse/arvados_fuse/unmount.py

diff --git a/services/fuse/arvados_fuse/unmount.py b/services/fuse/arvados_fuse/unmount.py
index db78ddc738..a72da3a8dc 100644
--- a/services/fuse/arvados_fuse/unmount.py
+++ b/services/fuse/arvados_fuse/unmount.py
@@ -1,3 +1,7 @@
+# Copyright (C) The Arvados Authors. All rights reserved.
+#
+# SPDX-License-Identifier: AGPL-3.0
+
 import collections
 import errno
 import os
@@ -26,7 +30,55 @@ def mountinfo():
     return mi
 
 
-def unmount(path, timeout=10, recursive=False):
+def paths_to_unmount(path, mnttype):
+    paths = []
+    for m in mountinfo():
+        if m.path == path or m.path.startswith(path+"/"):
+            paths.append(m.path)
+            if not (m.is_fuse and (mnttype is None or
+                                   mnttype == m.mnttype)):
+                raise Exception(
+                    "cannot unmount {}: mount type is {}".format(
+                        path, m.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.
 
     Unmounting is done by writing 1 to the "abort" control file in
@@ -41,17 +93,23 @@ def unmount(path, timeout=10, recursive=False):
     fuse mount at all. Raises an exception if it cannot be unmounted.
     """
 
-    path = os.path.realpath(path)
+    path, _ = safer_realpath(path)
+
+    if subtype is None:
+        mnttype = None
+    elif subtype == '':
+        mnttype = 'fuse'
+    else:
+        mnttype = 'fuse.' + subtype
 
     if recursive:
-        paths = []
-        for m in mountinfo():
-            if m.path == path or m.path.startswith(path+"/"):
-                paths.append(m.path)
-                if not m.is_fuse:
-                    raise Exception(
-                        "cannot unmount {}: non-fuse mountpoint {}".format(
-                            path, m))
+        paths = paths_to_unmount(path, mnttype)
+        if not paths:
+            # We might not have found any mounts merely because path
+            # contains symlinks, so we should resolve them and try
+            # again. We didn't do this from the outset because
+            # realpath() can hang (see explanation below).
+            paths = paths_to_unmount(os.path.realpath(path), mnttype)
         for path in sorted(paths, key=len, reverse=True):
             unmount(path, timeout=timeout, recursive=False)
         return len(paths) > 0
@@ -66,15 +124,34 @@ def unmount(path, timeout=10, recursive=False):
     while True:
         mounted = False
         for m in mountinfo():
-            if m.is_fuse:
+            if m.is_fuse and (mnttype is None or mnttype == m.mnttype):
                 try:
-                    if os.path.realpath(m.path) == path:
+                    if m.path == path:
                         was_mounted = True
                         mounted = True
                         break
                 except OSError:
                     continue
-        if not mounted:
+        if not was_mounted and path != os.path.realpath(path):
+            # If the specified path contains symlinks, it won't appear
+            # verbatim in mountinfo.
+            #
+            # It might seem like we should have called realpath() from
+            # the outset. But we can't: realpath() hangs (in lstat())
+            # if we call it on an unresponsive mount point, and this
+            # is an important and common scenario.
+            #
+            # By waiting until now to try realpath(), we avoid this
+            # problem in the most common cases, which are: (1) the
+            # specified path has no symlinks and is a mount point, in
+            # which case was_mounted==True and we can proceed without
+            # calling realpath(); and (2) the specified path is not a
+            # mount point (e.g., it was already unmounted by someone
+            # else, or it's a typo), and realpath() can determine that
+            # without hitting any other unresponsive mounts.
+            path = os.path.realpath(path)
+            continue
+        elif not mounted:
             return was_mounted
 
         if attempted:
@@ -89,7 +166,7 @@ def unmount(path, 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