Calculate virtual size of image

Change-Id: I55d8193090dea749502a053fd348d92f67f3c012
Implements: blueprint image-introspect-plugin

specs/victoria/approved/glance/calculate-virtual-size.rst

@@ -0,0 +1,147 @@
+===============================
+Calculate virtual size of image
+===============================
+
+https://blueprints.launchpad.net/glance/+spec/calculate-virtual-size
+
+'virtual_size' should be set on image to avoid running `qemu_img`
+operations on consumer nodes.
+
+Problem description
+===================
+
+Image has virtual_size field in images table but it is never set unless
+we use taskflow `introspect` to create image. Consumers of glance
+like nova or cinder never consume image before calculating virtual
+size, which means every time they call for image, they need to
+perform `qemu_img info` call to calculate the virtual size of the image.
+
+Use Case:
+---------
+
+'virtual_size' should be set on image to avoid running `qemu_img`
+operations on consumer nodes.
+
+Proposed change
+===============
+
+All supported sparse disk image formats (i.e. what glance calls disk_format)
+simulate a larger virtual disk than the actual data that is stored, and
+record that virtual size in metadata. We propose to add a handler for each of
+the formats that can examine the chunks while streaming the image to extract
+the relevant metadata to determine the virtual disk size.
+
+In glance, users can create images using two ways.
+1) Create image API
+2) Import image API
+
+With this change virtual size will be set to image even user tries to use any
+of above two methods to create the image. Also images created by nova
+(nova-snapshot except 'direct-to-backend snapshot') or cinder
+(volume-upload-to-image) will be able to set the virtual size to image as well.
+
+NOTE: To start with we are going to calculate virtual size for images which
+will have container-format ``bare`` or other ``uncompressed`` formats only.
+Later as and when required or expected we will enhance it for other
+container-formats.
+
+We will be performing this operation during uploading image data to glance
+store, so for image import this will happen during the actual import phase
+and not the stage phase.
+
+Alternatives
+------------
+
+None
+
+Data model impact
+-----------------
+
+None
+
+REST API impact
+---------------
+
+None
+
+Security impact
+---------------
+
+None
+
+Notifications impact
+--------------------
+
+None
+
+Other end user impact
+---------------------
+
+None
+
+Performance Impact
+------------------
+
+None
+
+Other deployer impact
+---------------------
+
+None
+
+Developer impact
+----------------
+
+None
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  danms
+
+Other contributors:
+  None
+
+Reviewers
+---------
+
+Core reviewer(s):
+    abhishek-kekane
+    jokke
+    rosmaita
+
+Other reviewer(s):
+    whoami-rajat
+
+Work Items
+----------
+
+- Add handler for each of the disk-format
+- Add wrapper around chunked reader to calculate virtual size
+- Add unit tests for coverage
+- Add functional tests
+
+Dependencies
+============
+
+None
+
+Testing
+=======
+
+Tempest test to verify that virtual size is set on image using glance,
+nova snapshot and cinder upload-to-image operations.
+
+Documentation Impact
+====================
+
+Please refer to 'Other deployer impact'
+
+References
+==========
+
+https://review.opendev.org/#/c/744234