[9fans] namespaces, Alef

[9fans] namespaces, Alef

[faif]

Some questions that came up while reading the first paper (Plan 9 from
Bell Labs):

a) It seems that the potential of namespaces can be exposed only when
using a distributed environment with multiple machines (CPU servers,
file servers, terminals, etc.). Can I get a feeling about what a
namespace is in practice if I only own a single system installed on a
virtual machine?

b) I know that Limbo is mostly used in Inferno, but is Alef or Limbo
used in any parts of the native Plan 9? According to wikipedia (http://
en.wikipedia.org/wiki/Alef_%28programming_language%29) the Alef parts
were rewritten in C.

[9fans] namespaces, Alef

[Jack Norton]

faif wrote:
> Some questions that came up while reading the first paper (Plan 9 from
> Bell Labs):
> 
> a) It seems that the potential of namespaces can be exposed only when
> using a distributed environment with multiple machines (CPU servers,
> file servers, terminals, etc.). Can I get a feeling about what a
> namespace is in practice if I only own a single system installed on a
> virtual machine?
> 

You are forgetting about per-process namespaces.  For instance, when you 
run httpd, a custom namespace gets constructed that is unique to it. 
Typically '/usr/web' gets bound to / in the namespace of httpd (among 
other things).  Also certain things *don't* get bound too.  Why would 
httpd need to access eia0? Don't put it in the namespace.

The very point of all of this capability is that it is completely 
transparent to all things being on one machine, or on 20 machines.

> b) I know that Limbo is mostly used in Inferno, but is Alef or Limbo
> used in any parts of the native Plan 9? According to wikipedia (http://
> en.wikipedia.org/wiki/Alef_%28programming_language%29) the Alef parts
> were rewritten in C.
> 

I'm pretty sure there is no Alef left in the latest.  There is no Limbo 
either.  I could be wrong.


-Jack

[9fans] namespaces, Alef

[erik quanstrom]

> a) It seems that the potential of namespaces can be exposed only when
> using a distributed environment with multiple machines (CPU servers,
> file servers, terminals, etc.). Can I get a feeling about what a
> namespace is in practice if I only own a single system installed on a
> virtual machine?

false.

the system would not function without namespaces.

for example, a search path is usually not used.  bin is constructed from
several underlying directories; often /$objtype/bin /rc/bin $home/bin/$objtype
$home/bin/rc.  

the same goes for the construction of /dev.  /dev is constructed from
a number of file servers, such as #c. #P, #$, #S, #r, #i, #m, #v, #u, #t,
#?, #?.

there's no reason you can't write a user-level file system that provides
a "device" that lives in /dev.

ramfs is simple, but perhaps the most consistently useful example.
ramfs mounts a ram disk on /tmp.  then you can scribble away, and
when you're done, you can just delete the window, or unmount /tmp.
you can run many independent ramfs at once.

> b) I know that Limbo is mostly used in Inferno, but is Alef or Limbo
> used in any parts of the native Plan 9? According to wikipedia (http://
> en.wikipedia.org/wiki/Alef_%28programming_language%29) the Alef parts
> were rewritten in C.

true.

- erik