mounts: support reliably detecting and using Azure ephemeral disks

Azure's ephemeral disks are not guaranteed to be assigned the same name by
the kernel every boot. This causes problems on ~2% of Azure instances, and
can be fixed by using udev rules to give us a deterministic path to mount;
this patch introduces those udev rules and modifies the Azure data source
to use them.

Changes to a couple of config modules were also required. In some places,
they just needed to learn to dereference symlinks. In cc_mounts this
wasn't sufficient because the dereferenced device would have been put in
/etc/fstab (rather defeating the point of using the udev rules in the
first place). A fairly hefty refactor was required to separate "is this a
valid block device?" from "what shall I put in fstab?".

LP: #1411582

1 files changed, 18 insertions, 0 deletions

diff --git a/udev/66-azure-ephemeral.rules b/udev/66-azure-ephemeral.rules
new file mode 100644
index 00000000..b9c5c3ef
--- /dev/null
+++ b/udev/66-azure-ephemeral.rules
@@ -0,0 +1,18 @@
+# Azure specific rules
+ACTION!="add|change", GOTO="cloud_init_end"
+SUBSYSTEM!="block", GOTO="cloud_init_end"
+ATTRS{ID_VENDOR}!="Msft", GOTO="cloud_init_end"
+ATTRS{ID_MODEL}!="Virtual_Disk", GOTO="cloud_init_end"
+
+# Root has a GUID of 0000 as the second value
+# The resource/resource has GUID of 0001 as the second value
+ATTRS{device_id}=="?00000000-0000-*", ENV{fabric_name}="azure_root", GOTO="ci_azure_names"
+ATTRS{device_id}=="?00000000-0001-*", ENV{fabric_name}="azure_resource", GOTO="ci_azure_names"
+GOTO="cloud_init_end"
+
+# Create the symlinks
+LABEL="ci_azure_names"
+ENV{DEVTYPE}=="disk", SYMLINK+="disk/cloud/$env{fabric_name}"
+ENV{DEVTYPE}=="partition", SYMLINK+="disk/cloud/$env{fabric_name}-part%n"
+
+LABEL="cloud_init_end"