mounts: document weird prefix in schema (#1913)

Add test and support for parsing IEC prefix format.

3 files changed, 22 insertions, 3 deletions

diff --git a/cloudinit/config/schemas/schema-cloud-config-v1.json b/cloudinit/config/schemas/schema-cloud-config-v1.json
index a91dc482..7ff80ce3 100644
--- a/cloudinit/config/schemas/schema-cloud-config-v1.json
+++ b/cloudinit/config/schemas/schema-cloud-config-v1.json
@@ -1764,7 +1764,7 @@
               "description": "Path to the swap file to create"
             },
             "size": {
-              "description": "The size in bytes of the swap file, 'auto' or a human-readable size abbreviation of the format <float_size><units> where units are one of B, K, M, G or T.",
+              "description": "The size in bytes of the swap file, 'auto' or a human-readable size abbreviation of the format <float_size><units> where units are one of B, K, M, G or T. **WARNING: Attempts to use IEC prefixes in your configuration prior to cloud-init version 23.1 will result in unexpected behavior. SI prefixes names (KB, MB) are required on pre-23.1 cloud-init, however IEC values are used. In summary, assume 1KB == 1024B, not 1000B**",
               "oneOf": [
                 {
                   "enum": [
diff --git a/cloudinit/util.py b/cloudinit/util.py
index 078ce1c2..96cd1b74 100644
--- a/cloudinit/util.py
+++ b/cloudinit/util.py
@@ -2761,11 +2761,25 @@ def read_meminfo(meminfo="/proc/meminfo", raw=False):
 
 def human2bytes(size):
     """Convert human string or integer to size in bytes
+
+    In the original implementation, SI prefixes parse to IEC values
+    (1KB=1024B). Later, support for parsing IEC prefixes was added,
+    also parsing to IEC values (1KiB=1024B). To maintain backwards
+    compatibility for the long-used implementation, no fix is provided for SI
+    prefixes (to make 1KB=1000B may now violate user expectations).
+
+    Future prospective callers of this function should consider implementing a
+    new function with more standard expectations (1KB=1000B and 1KiB=1024B)
+
+    Examples:
     10M => 10485760
-    .5G => 536870912
+    10MB => 10485760
+    10MiB => 10485760
     """
     size_in = size
-    if size.endswith("B"):
+    if size.endswith("iB"):
+        size = size[:-2]
+    elif size.endswith("B"):
         size = size[:-1]
 
     mpliers = {"B": 1, "K": 2**10, "M": 2**20, "G": 2**30, "T": 2**40}
diff --git a/tests/unittests/test_util.py b/tests/unittests/test_util.py
index cc516942..fe933c0a 100644
--- a/tests/unittests/test_util.py
+++ b/tests/unittests/test_util.py
@@ -2648,6 +2648,11 @@ class TestHuman2Bytes:
             with pytest.raises(ValueError):
                 util.human2bytes(test_i)
 
+    def test_ibibytes2bytes(self):
+
+        assert util.human2bytes("0.5GiB") == 536870912
+        assert util.human2bytes("100MiB") == 104857600
+
 
 class TestKernelVersion:
     """test kernel version function"""