Erlang filesystem

[Ulf Wiger]

On Fri, 9 May 2003, Chris Pressey wrote:

>On Thu, 17 Apr 2003 Ulf Wiger <etxuwig@REDACTED> wrote:
>> A common setup is to keep the same code on all nodes -- i.e.
>> identical application trees. One very good reason for doing
>> this is to avoid having different versions of the same
>> module in the system.
>
>This is one of the things that got me thinking about a
>replicated file system.
>
>It would be interesting to know how people handle keeping
>their code in synch across nodes - i.e., what's most
>popular - rpc:multicall(code, load_binary, [Mod, Bin,
>File])?  rsync?  Manually copying the code over when it
>changes?  Using the release handler somehow?

The release handler works well for this. It's designed to
support synchronized upgrade on multiple nodes.


>It IS trivial to read an entire file from another node:
>
>  > rpc:call(catbus@REDACTED, file, read_file, [".cshrc"]).
>  {ok,<<35,32,36,70,114,101,101,66,83,68,58,32,115,114,99,47,115,
>  104,97,114,101,47,115,107,101,108,47,...>>}
>
>But when I try just opening it:
>
>  > {ok,H} = rpc:call(catbus@REDACTED, file, open, [".cshrc",
>  [read]]).
>  {ok,<3931.59.0>}
>  > rpc:call(catbus@REDACTED, file, read, [H, 100]).
>  {error,terminated}
>  > file:format_error({error,terminated}).
>  "unknown POSIX error"

Not sure why you get 'terminated', but a problem with doing
it this way is that the rpc:call/3 will be executed in a
temporary process on catbus; when the call completes, the
process is terminated, and since it is the owner of the file
descriptor, the file will be closed automatically.

I think what you want to do is to run your other nodes as
loader slaves to catbus. It's not incredibly clear from the
documentation (or I haven't found the place in the
documentation where it's clearly described) how to do this.
You may try with erl -loader inet -hosts ...

or reading the code in file_server.erl, one might perhaps
try erl -master catbus@REDACTED, but that doesn't seem
to work for me, and I don't find any documentation on it.

(I'm sorry I can't give you a working example. From a
cursory glance, it's not obvious to me how one tests an
erlang node using another erlang node on the same host as a
boot loader (it seems consistent with the erlang philosophy
that one should be able to do this), and I'm not sure if you
need to use a boot server in order to have a file server.
I'm sure this is explained in the docs somewhere, but it's
late, and I intend to go home and get some sleep.)

/Uffe
-- 
Ulf Wiger, Senior Specialist,
   / / /   Architecture & Design of Carrier-Class Software
  / / /    Strategic Product & System Management
 / / /     Ericsson AB, Connectivity and Control Nodes