Re: On plugins, on-disk formatting and such

[Alex Zarochentsev <zam@namesys.com>]

On Sat, Apr 10, 2004 at 01:07:01PM +0300, Markus Törnqvist wrote:
> First off I'd like to thank the Namesys guys for their excellent work,
> the latest snapshot has been very stable for me, so stable in fact
> that my life is boring because of it ;)
> 
> I have like a ton of questions so I'll just put them in this mail and
> see which points get replied to. Hopefully all ;)
> 
> 1) The xattrs issue never got any replies, although I gathered that it
>    would be possible to map xattr calls to the Reiser4 API.
>    Is this fact or fiction? What will the Reiser4 API look like, apart
>    from control files?

xattrs are possible but we have no plans to use them.  
2 APIs are: pseudo files and reiser4 syscall.

> 
> 2) Is metadata stored anywhere? If I want to organize all my libs in one
>    fibre, I make it so, I reboot and do I then have to reset the fibration
>    for the directory? Is it possible to have persistency here? Wouldn't
>    a wrong fibration type make the files inaccessible?
>    Is this addressed in the Reiser4 API somehow?

reiser4 is able to store plugin sets (list of plugin ids for the object) as 
a part of the object's stat data.

> 
> 3) How big are the chances that the on-disk layout will still change?
>    On IRC I've got the impression that the chance is next to none,
>    and I thank you for that!
>    Still, a lot of people are hesitant to try Reiser4 because of this
>    fear. Doing an mkfs is not a small thing and some assurance would
>    surely bring along community testing support.
> 
> 4) http://thebsh.namesys.com/snapshots/2004.03.26/READ.ME
>    4.1) I have used Reiser4 as my rootfs for a long, long time.
>         Why does the READ.ME say I can't do it?-) I just never mount
>         it read-only, so I don't have to remount it read-write and it
>         just works. Is there something amiss here?
>    
>    4.2) What exactly does it mean that CONFIG_REISER4_COPY_ON_CAPTURE
>         is stabler than before? Is it soon safe to configure in?
>         Is it possible for me to test it on only one filesystem or
>         do I risk rootfs (and home directory) stability by trying it
>         out? If I compile it in, what's the best way of testing it?

we still see fs errors if COC enable. they are rare now, but COC is not stable
yet.

> 
> 5) If I wanted to write an fs plugin, I gathered that I would not have
>    to mkfs again. Should this not require some persistency in metadata?
>    I also gathered that Hans Reiser is against loadable kernel modules
>    that are in essence filesystem plugins. Is this because a stray
>    rmmod might cause breakage or something else?
>    One of the good things for me in Linux is that I can use honest
>    modules to try something, rmmod, recompile, insmod and I don't
>    think this is any different.
> 
> 6) I understood there are some NFS issues still left, what other issues
>    are there? Is it possible to have some TODO list on the web so
>    people could guess at what's going on? (BTW, Nikita, that doesn't
>    mean I won't bug you in the future ;)
> 
> 7) http://namesys.com/benchmarks.html#slow.2004.03.26
>    That is awesome. Could someone give a brief, or rather human-readable,
>    explanation on why Reiser4 refuses to slow down under those loads?
>    Not that I'd find those benchmarks hard to swollow per se, I did
>    see Reiser4 perform superior for myself.
>    But what is the secret? Atomic transactions?

I think it is a feature of delayed block allocation. 

> 
> Thanks again for the good work and I hope this brings along some discussion
> more interesting than the metas/ thread!

> 
> -- 
> mjt
> 

-- 
Alex.