Commits on Mar 8, 2015

1. Gracefully handle race condition in `makedirs' …

   Problem
   -------
   
   In the imperative sequence::
   
      if not os.path.isdir(folder_name):
          os.makedirs(folder_name)
   
   There exists the possibility that another process may create ``folder_name``
   between the system path test and the system folder construction.  This is
   especially true when launching both the salt-minion and salt-master
   simultaneously::
   
       # systemctl status -l salt-minion salt-master
       * salt-minion.service - The Salt Minion
          Loaded: loaded (/usr/lib/systemd/system/salt-minion.service; enabled)
          Active: inactive (dead) since Sat 2015-03-07 21:38:53 UTC; 7h ago
         Process: 1168 ExecStart=/usr/bin/salt-minion (code=exited, status=0/SUCCESS)
        Main PID: 1168 (code=exited, status=0/SUCCESS)
   
       Mar 07 21:36:29 local.dev systemd[1]: Started The Salt Minion.
       Mar 07 21:38:53 local.dev salt-minion[1168]: [ERROR   ] Attempt to authenticate with the salt master failed
   
       * salt-master.service - The Salt Master Server
          Loaded: loaded (/usr/lib/systemd/system/salt-master.service; enabled)
          Active: failed (Result: exit-code) since Sat 2015-03-07 21:37:53 UTC; 7h ago
         Process: 1166 ExecStart=/usr/bin/salt-master (code=exited, status=17)
        Main PID: 1166 (code=exited, status=17)
   
       Mar 07 21:37:52 local.dev salt-master[1166]: Failed to create path "/var/log/salt/master" - [Errno 17] File exists: '/var/log/salt'
       Mar 07 21:37:53 local.dev systemd[1]: salt-master.service: main process exited, code=exited, status=17/n/a
       Mar 07 21:37:53 local.dev systemd[1]: Failed to start The Salt Master Server.
       Mar 07 21:37:53 local.dev systemd[1]: Unit salt-master.service entered failed state.
   
   In such cases, the salt-minion tested for the non-existence (true), then
   salt-master also tested (true).  salt-minion created the folder, but
   salt-master failed (with Errno 17: File exists).
   
   Solution
   --------
   
   Do not test for path existence at all, always create, expecting errno.EEXISTS
   as an acceptable condition.  This delegates responsibility of handling such
   "race conditions" to the kernel where locks exist to prevent it.

   

   jquast committed Mar 8, 2015
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