Fix handling of value-less extended attributes

3 files changed, 32 insertions, 2 deletions

diff --git a/NEWS b/NEWS
index 178f3129..16750715 100644
--- a/NEWS
+++ b/NEWS
@@ -20,6 +20,8 @@ Bug fixes:
 
 * Empty values for extended attributes are now backed up correctly.
   Previously they would cause an infinite loop.
+* Extended attributes without values are now ignored. This is different
+  from attributes with empty values. Reported by Vladimir Elisseev.
 * An empty port number in sftp URLs is now handled correctly. Found based
   on report by Anton Shevtsov.
 * A bad performance bug when backing up full systems (starting from the
diff --git a/obnamlib/metadata.py b/obnamlib/metadata.py
index be3a46c9..eaca40fb 100644
--- a/obnamlib/metadata.py
+++ b/obnamlib/metadata.py
@@ -14,11 +14,14 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 
+import errno
 import grp
+import logging
 import os
 import pwd
 import stat
 import struct
+import tracing
 
 import obnamlib
 
@@ -127,10 +130,35 @@ def _cached_getgrgid(gid): # pragma: no cover
 
 
 def get_xattrs_as_blob(fs, filename): # pragma: no cover
+    tracing.trace('filename=%s' % filename)
     names = fs.llistxattr(filename)
+    tracing.trace('names=%s' % repr(names))
     if not names:
         return None
-    values = [fs.lgetxattr(filename, name) for name in names]
+
+    values = []
+    for name in names[:]:
+        tracing.trace('trying name %s' % repr(name))
+        try:
+            value = fs.lgetxattr(filename, name)
+        except OSError, e:
+            # On btrfs, at least, this can happen: the filesystem returns
+            # a list of attribute names, but then fails when looking up
+            # the value for one or more of the names. We pretend that the
+            # name was never returned in that case.
+            #
+            # Obviously this can happen due to race conditions as well.
+            if e.errno == errno.ENODATA:
+                names.remove(name)
+                logging.warning(
+                    '%s has extended attribute named %s without value, '
+                    'ignoring attribute' % (filename, name))
+            else:
+                raise
+        else:
+            tracing.trace('lgetxattr(%s)=%s' % (name, value))
+            values.append(value)
+    assert len(names) == len(values)
 
     name_blob = ''.join('%s\0' % name for name in names)
 
diff --git a/obnamlib/vfs_local.py b/obnamlib/vfs_local.py
index e4b6b274..9b456f9f 100644
--- a/obnamlib/vfs_local.py
+++ b/obnamlib/vfs_local.py
@@ -168,7 +168,7 @@ class LocalFS(obnamlib.VirtualFileSystem):
     def lgetxattr(self, filename, attrname): # pragma: no cover
         ret = obnamlib._obnam.lgetxattr(self.join(filename), attrname)
         if type(ret) is int:
-            raise OSError((ret, os.strerror(ret), filename))
+            raise OSError(ret, os.strerror(ret), filename)
         return ret
 
     def lsetxattr(self, filename, attrname, attrvalue): # pragma: no cover