System SSH key upgrader

agent/agent.go

 // Copyright 2013 Canonical Ltd.
 // Licensed under the AGPLv3, see LICENCE file for details.
 
 package agent
 
 import (
         "fmt"
         "path"
         "regexp"
         "sync"
@@ skipping 390 matching lines @@
 }
 
 func (c *configInternal) Write() error {
         // Lock is taken prior to generating any content to write.
         configMutex.Lock()
         defer configMutex.Unlock()
         return currentFormatter.write(c)
 }
 
 func (c *configInternal) WriteUpgradedToVersion(newVersion version.Number) error {
+        originalVersion := c.upgradedToVersion
         c.upgradedToVersion = newVersion
-        return c.Write()
+        err := c.Write()
+        if err != nil {
+                // We don't want to retain the new version if there's been an error writing the file.
+                c.upgradedToVersion = originalVersion
+        }
+        return err
 }
 
 func (c *configInternal) WriteCommands() ([]string, error) {
         return currentFormatter.writeCommands(c)
 }
 
 func (c *configInternal) OpenAPI(dialOpts api.DialOpts) (st *api.State, newPassword string, err error) {
         info := api.Info{
                 Addrs:    c.apiDetails.addresses,
                 Password: c.apiDetails.password,
@@ skipping 44 matching lines @@
                 }
                 // TODO(rog) remove this fallback behaviour when
                 // all initial connections are via the API.
                 if !errors.IsUnauthorizedError(err) {
                         return nil, err
                 }
         }
         info.Password = c.oldPassword
         return state.Open(&info, state.DefaultDialOpts(), policy)
 }