Truncate fail_reason to column length

During create_backup failure handling, backup_update fails with
DataError ("Data too long for column") if the fail_reason is
greater than 255 characters. As a result, backup status is stuck
in 'creating' state. This patch avoids the problem by truncating
fail_reason to 255 characters before update.

Closes-Bug: #1376199
Change-Id: If0d616b81d3869f7ea110caab8cf4140cf5c5c9e

cinder/db/sqlalchemy/models.py

@@ -24,7 +24,7 @@ from oslo.db.sqlalchemy import models
 from sqlalchemy import Column, Integer, String, Text, schema
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy import ForeignKey, DateTime, Boolean
-from sqlalchemy.orm import relationship, backref
+from sqlalchemy.orm import relationship, backref, validates
 
 from cinder.openstack.common import timeutils
 
@@ -478,6 +478,10 @@ class Backup(BASE, CinderBase):
     size = Column(Integer)
     object_count = Column(Integer)
 
+    @validates('fail_reason')
+    def validate_fail_reason(self, key, fail_reason):
+        return fail_reason and fail_reason[:255] or ''
+
 
 class Encryption(BASE, CinderBase):
     """Represents encryption requirement for a volume type.

cinder/tests/test_db_api.py

@@ -1237,6 +1237,19 @@ class DBAPIBackupTestCase(BaseTest):
         self._assertEqualObjects(updated_values, updated_backup,
                                  self._ignored_keys)
 
+    def test_backup_update_with_fail_reason_truncation(self):
+        updated_values = self._get_values(one=True)
+        fail_reason = '0' * 512
+        updated_values['fail_reason'] = fail_reason
+
+        update_id = self.created[1]['id']
+        updated_backup = db.backup_update(self.ctxt, update_id,
+                                          updated_values)
+
+        updated_values['fail_reason'] = fail_reason[:255]
+        self._assertEqualObjects(updated_values, updated_backup,
+                                 self._ignored_keys)
+
     def test_backup_destroy(self):
         for backup in self.created:
             db.backup_destroy(self.ctxt, backup['id'])