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On 6/15/18 7:17 PM, Dave Chinner wrote:
> On Thu, Jun 14, 2018 at 09:45:49PM -0500, Eric Sandeen wrote:
>>
>>
>> On 6/14/18 9:33 PM, Dave Chinner wrote:
>>> On Thu, Jun 14, 2018 at 07:10:09PM -0700, Luis R. Rodriguez wrote:
>>>> Silly mobile gmail interface not letting me bottom-post... What if we treat
>>>> no version being present as version 0?
>>>
>>> We haven't released anything yet so we should put it in there from
>>> the start rather than having to work around the lack of a version
>>> field later.
>>
>> So, pretend I'm dumb ('cause I often am) and spell it out for me, what would
>> we do with a version?
>>
>> If a config file contains a section or token that some version of mkfs doesn't
>> understand, it'll fail.
>>
>> If we try to read a config file with a too-new version, we'd ... fail?
>
> Fail with a useful error message, rather than do something
> unexpected or incorrect.
like "section 'foo' uknown" or "token 'bar' unknown?"
We'd do that today...
> Let's face it - the config file is a persistent, on-disk structure
> that we have to handle in both forwards and backwards compatible
> manners for many, many years. It's no different to the on-disk
> format in that respect. Why wouldn't we apply the same guards for
> format changes we apply to syscalls, ioctls, on-disk formats, etc
> that all have the same long term compatibility requirements?
Indeed, with on-disk formats we have compat, incompat, ro-compat ....
Are you proposing forward and backward, compat/imcompat ... tokens?
Pobably not.
Disk formats have that because we may corrupt the things around us if
we don't understand the existence of a new metadata type; others we can
safely ignore.
With ioctls we have a set size; the only time we have versions is if we
have padding that should now be parsed in a newer version.
I'm trying to find a concrete example of how an incompatible config
file version would fail more gracefully than an unknown section/token already
fails today. Maybe I lack imagination, but help me out?
In the abstract it sounds good. In practice, I'm not yet seeing it.
-Eric
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