Re: [9fans] question about union dirs

["Russ Cox" <rsc@plan9.bell-labs.com>]

> 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