Re: [9fans] Ephase question.

["Roman V. Shaposhnick" <vugluskr@unicorn.math.spbu.ru>]

On Mon, Aug 12, 2002 at 09:39:40PM -0400, presotto@plan9.bell-labs.com wrote:
> This isn't new semantics.  If you remove a file that someone
> else is using, too bad for him.  There's nothing sacred about
> having a file open.

  Indeed. Same applies to any fid, not just opened ones.

> If someone else has permissions to do nasty and nefarious things to it,
> they can.
>
> This is very different than Unix.

  I see. But can you give me any insight into why it was implemented this
  way. Again, it seems so obvious to use fids for reference counting and it
  shouldn't be of a significant overhead. Moreover it's entirely up to
  the FileServer to support this feature -- kernel is not supposed to
  care. You should've had some reason for not supporting this in all
  your FileServers.

Thanks,
Roman.

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> From: "Roman V. Shaposhnick" <vugluskr@unicorn.math.spbu.ru>
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> Date: Tue, 13 Aug 2002 05:26:18 +0400
>
> Hi everybody,
>
> digging inside 4th edition gave me some very unexpected results
> in terms of file access semantics in user space. But let me show
> a scenario first:
>
> first-user$ cat > /shared-directory/file
> blah-blah-blah
>
> second-user$ rm /shared-directory/file
>
> [first user after hitting <CR> ]
> "phase error -- directory entry not allocated"
>
> I was a little bit shocked at first, mainly because I've got so used to
> UNIX semantics of "once you get it -- it's yours", that I've been taking
> it for granted in Plan9 as well.
>
> Suddenly I can't remember how 3nd and 2nd editions behaved.
>
> Before now I was under the impression that regular unopened fids are mostly
> used for reference counting and once you grab a fid nobody can kill the
> actual object it refers to, but 4th edition proved me wrong. Even though
> I still can't understand why it behaves this way. Could somebody explain
> the rationale behind that to me, please ? And I'm really curios now about
> what obligations server is supposed to have when it accepts a new fid from
> a client for a given object.
>
> Thanks,
> Roman.