Re: [9fans] question about union dirs

Re: [9fans] question about union dirs

[vic]

Sounds reasonable.

> If a remote server gets disconnected from
> your machine, then the TCP or IL connection breaks

In the TCP case, suppose this search is the first
operation since the disconnection occurred (no prior
outstanding tcp transmissions).  Does the search block
until TCP gives up (13 or so minutes later), or is
the "hungup" condition somehow marked sooner?

> and that part of the union is marked as ``hungup''
> and ignored.

Can the user (of say rc) discover this?  For example,
suppose I expect to be getting /bin/foo from the
disconnected service.  If I quietly get a different
/bin/foo from something further down the union, I might
be baffled.

Vic

Re: [9fans] question about union dirs

[Russ Cox]

> In the TCP case, suppose this search is the first
> operation since the disconnection occurred (no prior
> outstanding tcp transmissions).  Does the search block
> until TCP gives up (13 or so minutes later), or is
> the "hungup" condition somehow marked sooner?

Yes, it blocks, but TCP should give up after 30 seconds.

> Can the user (of say rc) discover this?  For example,
> suppose I expect to be getting /bin/foo from the
> disconnected service.  If I quietly get a different
> /bin/foo from something further down the union, I might
> be baffled.

If the user knew what the mount number for
that connection was, ls -l would show different
numbers.  For example:

g% ls -l /n/kfs/adm/users
--rw-rw-r-- M 25 adm adm 140 Aug 28 08:37 /n/kfs/adm/users
g% ls -l /n/emelie/adm/users
--rw-rw-r-- M 57 adm adm 10458 Jul 19 11:08 /n/emelie/adm/users
g% ls -l /n/kfs/adm/users
--rw-rw-r-- M 57 adm adm 10458 Jul 19 11:08 /n/kfs/adm/users
g% ls -l /n/kfs/adm|grep users
--rw-rw-r-- M 57 adm      adm   10458 Jul 19 11:08 /n/kfs/adm/users
--rw-rw-r-- M 25 adm      adm     140 Aug 28 08:37 /n/kfs/adm/users
g%

The 'M 25' says that this file is coming from the
mount device (it's a 9P service rather than a kernel
device) instance number 25.  Each mount gets a
different instance number.

Russ

Re: [9fans] question about union dirs

[Russ Cox]

If a remote server gets disconnected from
your machine, then the TCP or IL connection breaks
and that part of the union is marked as ``hungup''
and ignored.

Russ

[9fans] question about union dirs

[vic]

[ I tried to post this to comp.os.plan9 on Weds, but
  it has not appeared yet. ]

When Plan 9 searches for a name in a union directory,
what happens when one or more of the member directories
in unavailable (because, say, the machine is
temporarily disconnected from that directory's file
server)?

Does the whole search block until the individual one
completes?  Or is it skipped once the kernel, somehow,
determines that it is unavailable?  Or something else?

Thanks.

Vic