Re: [PATCH RFC] fs: New zonefs file system

[Damien Le Moal <Damien.LeMoal@wdc.com>]

On 2019/07/22 9:05, Dave Chinner wrote:
> On Sat, Jul 20, 2019 at 07:15:26AM +0000, Damien Le Moal wrote:
>> Jeff,
>>
>> On 2019/07/19 23:25, Jeff Moyer wrote:
>>> OK, I can see how a file system eases adoption across multiple
>>> languages, and may, in some cases, be easier to adopt by applications.
>>> However, I'm not a fan of the file system interface for this usage.
>>> Once you present a file system, there are certain expectations from
>>> users, and this fs breaks most of them.
>>
>> Your comments got me thinking more about zonefs specifications/features and I am
>> now wondering if I am not pushing this too far in terms of simplicity. So here
>> is a new RFC/Question to chew on... While keeping as a target the concept of
>> "file == zone" or as close to it as possible, what do you think zonefs minimal
>> feature set should be ?
>>
>> One idea I have since a while back now is this:
>> 1) If a zone is unused, do not show a file for it. This means adding a dynamic
>> "zone allocation" code and supporting O_CREAT on open, unlink, etc. So have more
>> normal file system calls behave as with a normal FS.
>> 2) Allow file names to be decided by the user instead of using a fixed names.
>> Again, have O_CREAT behave as expected
> 
> So now you have to implement a persistent directory structure,
> atomic/transactional updates, etc. You've just added at least 2
> orders of magnitude complexity to zonefs and a very substantial
> amount of additional, ongoing QA to ensure it works correctly.
> 
> I think keeping it simple by exposing all zones to userspace and
> leaving it to the application to track/index what zones it is
> using is the simplest way forward for everyone.

OK. Anything more complicated would probably be better implemented within an
existing file system.

Thank you for your comments.

Best regards.

-- 
Damien Le Moal
Western Digital Research