Re: reiser4 plugins

[David Masover <ninja@slaphack.com>]

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Valdis.Kletnieks@vt.edu wrote:
> On Sun, 26 Jun 2005 23:10:43 EDT, Hubert Chan said:
> 
>>On Sun, 26 Jun 2005 20:40:29 -0400, Valdis.Kletnieks@vt.edu said:
> 
> 
>>Reiser4 plugins have to be compiled into the kernel.  (They're not
>>plugins in the sense that most people use that word.)  And any admin who
>>would compile that kind of plugin into the kernel needs to have his head
> 
> 
> Oh?  You saying that it *wont* be permitted for a user to say:
> 
> mkdir $HOME/zipped
> chattr "files under here are ZIP files" $HOME/zipped
> 
> and instead you have to do that chattr by hand for *every* *single* zip file?

chown works this way.  At least for username, there's no default user
possible per directory.  But scroll down a bit...

> Or "files on this filesystem are encrypted by default"?
> 
> I suspect that this sort of thing is going to be one of the *first* things
> that will get created, and any admin who tries to sell this idea to the users
> *without* that sort of functionality will be handed their head.

I think it may be possible to set defaults to a certain extent, but I
think that it's still actually a per-file setting whether the file is
encrypted.  Obviously, the keys have to be shared somehow, so there's
probably more grouping than just defaults...

There has been some mention of inheritance, but I've forgotten how
that's supposed to work.  If there's some sort of inheritance where
children inherit properties of their parent directory, and also inherit
changes to those properties, than Hans probably wants that to be the
prefered way of doing things?

I don't think there's that kind of inheritance, though.

> And notice that it doesn't *have* to be quite so obvious - how about if a
> user creates a directory $HOME/zipped/ and flags it as "anything under here
> is a zipped file".
> 
> Now throw in multiple users and CPU limits.  User A enters that directory and
> references everything, causing the buffer cache to get filled up.  While there,
> A makes changes, so the pages are dirty - "for i in */*; do echo " " >> $i; done"
> would do the job...  User B now does something that causes a writeback of one
> of those buffer cache pages.
> 
> A) What process currently gets ticked for the CPU and I/O for the writeback?
> 
> B) In your model, who will get ticked for the resources?
> 
> C) Will the users riot? (Note that you can't win here - currently, the "price"
> of writing back A's and B's pages are about equal.  However, if A gets dinked
> for an expensive writeback due to B's process, A will get miffed.  If B gets
> charge for an expensive writeback of A's, B will get miffed. If you say "screw it"
> and bill it to a kernel thread, the bean counters will get miffed... ;)

If I understand this correctly, this is somewhat like if user A creates
a 50 meg file on a system with 100 megs free RAM, and user B runs
"sync".  Also similar to if B were to suddenly fill up 75 megs of RAM,
forcing A's file to be flushed -- last I checked, in Reiser4, only a
sync or memory pressure causes writes to flush.

Right?  This is tempting to comment on, but I want to make sure I grok
it first...

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