Pytrivfs

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Python bindings for TrivFS.

Sommaire

1 TODO
2 QUESTIONS
3 HOWTO

TODO

Safe multithreading with Python
Finish Read support
Write support

QUESTIONS

off_t <=> int ?
Use inout instead of in parameters ?

HOWTO

How it work ?

Pytrivfs works with callbacks. For each action on the node, you can link a python callback to execute a piece of python code.

Currently, you can only create read-only translators and not all of the functions are implemented.

To start your translator, just use the usual way :

$ settrans -cgap node mytrans.py

or

$ settrans -cgap node python mytrans.py

if you don't want to make the .py file executable.

How to develop a python translator ?

First of all, you have to import the pytrivfs module in your namespace :

import pytrivfs

Then, for each callback, you have to define a function and associate it to an event using set_callback(). Here's an example of setting up a callback :

def start():
   dict = list()

   fd = open("langage", "r")
   lines = fd.readlines()
   for line in lines:
       dict.append(line.rstrip("\n"))
   fd.close()

pytrivfs.set_callback(pytrivfs.START, start)

The first argument is a constant defining where the callback will be hooked. The second one is the callback itself.

Once you have filled in your callbacks (you don't need to define them all, it will skip undefined ones), start with :

pytrivfs.start()

Callbacks

At bootstrap

Symbol : START
Arguments : -
Return : -

When asking to go away

Symbol : GOAWAY
Arguments : -
Return : -

When opening the node

Symbol : OPEN
Arguments : hook (A namespace for your needs)
Return : -

When reading

Symbol : IO_READ
Arguments : hook (A namespace for your needs), offs (The offset), amount (how much we want)
Return : data, offs, amount

When seeking

Symbol : IO_SEEK
Arguments : hook (A namespace for your needs), offs (The offset), how (0 : SEEK_SET, 1 : SEEK_CUR, 2 : SEEK_END)
Return : offs (the new offset)

Examples !

An http fetcher

#!/usr/bin/python
import sys, os, urllib

#Temp line, won't be necessary
sys.path.append('.')
import pytrivfs

# HTTP Translator
# A translator that fetch a webpage

def open_cb(hook):
    hook.off = -1

    sock = urllib.urlopen("http://www.hurdfr.org")
    hook.source = sock.read()
    sock.close()

def read_cb(hook, off, amount):
    length = len(hook.source)

    if off == -1:
        off = hook.off
    elif off < -1:
        off = 0

    if off > length:
        off = length

    if (off + amount) > length:
        amount = length - off

    hook.off += amount

    return hook.source, off, amount

def seek_cb(hook, offs, how):
    if how == 0:
        hook.off = offs
    elif how == 1:
        hook.off += offs
    elif how == 2:
        hook.off = len(hook.source) - offs

    return hook.off

pytrivfs.set_callback(pytrivfs.OPEN, open_cb)
pytrivfs.set_callback(pytrivfs.IO_READ, read_cb)
pytrivfs.set_callback(pytrivfs.IO_SEEK, seek_cb)

pytrivfs.start()