Comment 4 for bug 1471243

So, I did some investigation into our use of atime in glance. First, I noticed that we don't really rely on the last_accessed timestamp that we get back. We never actually use it. The only two places it's "used" is when listing cached images with `glance cache-manage` and in the `/v1/cached_images` endpoint. Other than that, we don't rely on it, and it isn't a critical piece of information for the operation of glance or its cache.

That said, in the module level docstring for the driver, Jay Pipes (going by git blame) specifically wrote that to use it you needed to ensure that noatime was not set. This is reasonable. The thing is that in glance_store, we will disable a driver if we're missing a prerequisite (e.g., a dependency, configuration, etc.). It's surprising to me that we aren't doing this with the cache drivers as well. It would seem perfectly logical to disable the xattr driver if the filesystem has noatime set.

Does this sound fair to everyone else?