lab 5 - signalfs v2


lab 5 - signalfs version 2; generalize and enhance the signalfs still further. Create a server that can load all the signal models, and each module has a connection directory per conversation.


Inferno 4th Edition 20040830.


The directory hierarchy presented by signalfs is now similar to ip(3).


One more requirement is that the server must be recursive, a signal module must be able to open other files served by the same signalfs. (The ds (3) device does this.)

To illustrate, say we implement a module to return a Fibonacci number. I use the clone mechanism so each client has it's own connection to the module. To read the fifth Fibonacci number

           d=/mnt/modfs/`{read 10}
           echo 5 >[1=0]
           read 10 < $d/data 
          }<> /mnt/modfs/clone

The module itself uses the ctl message to determine whether it should open a connection to clone and read the Fibonacci number for the number - 1. If the ctl number is 0 it returns 1, ending the recursion.

The module is a single function. The parameters are controlled by the ctl file, and the result is read from data.

The fileserver framework manages the clone and naming and loading of modules. I used wmexport.b as the starting point for building a framework.

2004/0918 21:28 The ip(3) device comes close to what I want. A directory for each proto (module); a clone below that, and a numbered directory for each instance. The numbered directory has ctl and data. The numbered directories aren't removed but keep state variable tracking whether in use.

What if we get a read on the data file from a process other than the opening process? We want to deny this.

2004/0919 16:51 Writing and debugging.

2004/0919 20:08 Is this something like spree, where the loaded module is an engine?

2004/0919 22:41 Given the layout of signalfs a filter is given the directory for the source module. The filter opens the clone file to get a connection. It then has exclusive access to that module. The filter exposes the same interface, so I could create multiple connections to that filter. But what if I want to alter the sinewave that the filter is reading from? Do I want shared write access to the sine ctl file? I'd need to know the connection the filter was reading from. No. The filter is in complete control of it's source.

2004/0921 22:01 Writeup and debugging.

Signalfs now knows nothing of the format of the signal. The signal is responsible for converting arrays of real to bytes. The signal interface has changed

          Signal: module {
           configstr: string;

           init: fn(args: list of string);
           config: fn(s: string): string;
           read: fn(n: int): array of byte;

Config returns an error string or nil if successful. Here's an example setup

          % mkdir mnt
          % signalfs mnt
          % echo add /usr/caerwyn/lab/5/wave.dis wave > mnt/ctl
          % lc mnt
          ctl   wave/
          % <> mnt/wave/clone {
           d=mnt/wave/`{read 10}
           echo file /usr/caerwyn/lab/3/sinewave.raw >[1=0]
           read 8 < $d/data | pcm


Here is the current version. signalfs.b, signal.m and the sinewave module again wave.b

Once this is debugged, I've reached the point where I can write all the signal modules. I still have no real plan for a sequencer. It may end up being shell script. I haven't tested the recursiveness yet.

I could have implemented signals using file2chan (2) except I am supporting the more complicated interface of clone, ctl and data. I hope it will be worth it having all the modules organized together under one server.

Tickfs might be better adapted to this interface. The ctl message for lookup are written to the ctl file, and I can control permission on the data file.

At some point I should provide a brief taxonomy of fileservers. E.g., as represented by ip(3), ds(3), file2chan, kfs (traditional), env(3), etc. Traditional file access from underlying storage (kfs, tarfs); Conversational object access (draw); Shared object access to virtual storage (env); Device interface (eia, audio); Single file but connection specific output: (using fid).



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