DataSourceEc2.py: remap dev names when metadata service disagress with kernel

device names presented in the metadata service may not be what the kernel
has named them.  This can be for more than 1 reason.  But some examples:
- device is virtio, metadata named 'sd'
- device is xvdX, metadata named sd

Those are the two situations that are covered here.  More complex, but
not covered are possibly:
- metadata service named device 'sda1', but it should actually be 'vdb1'

LP: #611137

1 files changed, 31 insertions, 2 deletions

diff --git a/cloudinit/DataSourceEc2.py b/cloudinit/DataSourceEc2.py
index e468bf50..cf50a3d5 100644
--- a/cloudinit/DataSourceEc2.py
+++ b/cloudinit/DataSourceEc2.py
@@ -24,6 +24,7 @@ import urllib2
 import time
 import sys
 import boto_utils
+import os.path
 
 class DataSourceEc2(DataSource.DataSource):
     api_ver  = '2009-04-04'
@@ -160,10 +161,38 @@ class DataSourceEc2(DataSource.DataSource):
         if not self.metadata.has_key('block-device-mapping'):
             return(None)
 
+        found = None
         for entname, device in self.metadata['block-device-mapping'].items():
             if entname == name:
-                return(device)
+                found = device
+                break
             # LP: #513842 mapping in Euca has 'ephemeral' not 'ephemeral0'
             if entname == "ephemeral" and name == "ephemeral0":
-                return(device)
+                found = device
+        if found == None:
+            cloudinit.log.warn("returning None")
+            return None
+
+        # LP: #611137
+        # the metadata service may believe that devices are named 'sda'
+        # when the kernel named them 'vda' or 'xvda'
+        # we want to return the correct value for what will actually
+        # exist in this instance
+        mappings = { "sd": ("vd", "xvd") }
+        ofound = found
+        short = os.path.basename(found)
+        
+        if not found.startswith("/"):
+            found="/dev/%s" % found
+
+        if os.path.exists(found):
+            return(found)
+
+        for nfrom, tlist in mappings.items():
+            if not short.startswith(nfrom): continue
+            for nto in tlist:
+                cand = "/dev/%s%s" % (nto, short[len(nfrom):])
+                if os.path.exists(cand):
+                    cloudinit.log.debug("remapped device name %s => %s" % (found,cand))
+                    return(cand)
         return None