pathauditor: change parts verification order to be root first
authorDurham Goode <durham@fb.com>
Thu, 11 Feb 2016 17:04:33 -0800
changeset 28087 0b7ce0b16d8a
parent 28086 65d24ca35496
child 28088 19424f960bf5
pathauditor: change parts verification order to be root first Previously, when we verified the parts of a path in the auditor, we would validate the deepest directory first, then it's parent, and so on up to the root. If there happened to be a symlink in the chain, that meant our first check would likely traverse that symlink. In some cases that symlink might point to a network filesystem that is expensive, and therefore this simple check could be very slow. The fix is to check the path parts starting at the root and working our way down. This has a minor performance difference in that we used to be able to short circuit from the audit if we reached a directory that had already been checked. Now we can't, but the cost is N dictionary look ups, where N is the number of parts in the path, which should be fairly minor.
mercurial/pathutil.py
--- a/mercurial/pathutil.py	Tue Jan 19 22:31:59 2016 +0900
+++ b/mercurial/pathutil.py	Thu Feb 11 17:04:33 2016 -0800
@@ -83,16 +83,17 @@
         parts.pop()
         normparts.pop()
         prefixes = []
-        while parts:
-            prefix = os.sep.join(parts)
-            normprefix = os.sep.join(normparts)
+        # It's important that we check the path parts starting from the root.
+        # This means we won't accidentaly traverse a symlink into some other
+        # filesystem (which is potentially expensive to access).
+        for i in range(len(parts)):
+            prefix = os.sep.join(parts[:i + 1])
+            normprefix = os.sep.join(normparts[:i + 1])
             if normprefix in self.auditeddir:
-                break
+                continue
             if self._realfs:
                 self._checkfs(prefix, path)
             prefixes.append(normprefix)
-            parts.pop()
-            normparts.pop()
 
         self.audited.add(normpath)
         # only add prefixes to the cache after checking everything: we don't