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From: Gary Wright <gwtmp01@mac.com>
Subject: Re: [9fans] Easiest way to make a filesystem
Date: Mon, 14 Jan 2008 16:00:13 -0500
To: Fans of the OS Plan 9 from Bell Labs <9fans@cse.psu.edu>
Topicbox-Message-UUID: 2e40bef6-ead3-11e9-9d60-3106f5b1d025


On Jan 14, 2008, at 3:10 PM, roger peppe wrote:
> i agree that it's too hard to create servers for simple filesystems.
>
> i've been wondering on and off for years what a "low-bar-to-entry"  
> filesystem
> creating library might look like, and my current thoughts go  
> something like:

I've been playing around with my own implementation of 9P in Ruby in  
an effort to explore this problem space and to better understand 9P.   
I don't know how many people on this list are familiar with ruby but  
it is pretty readable so I'll throw out some examples of my code and  
see what you think.  The example below does everything locally, but  
I've got facilities for connecting and serving via TCP and the 9P- 
wire protocol.

I'd appreciate comments/feedback.

class Example < Device
   class Root < Directory
     root               :mode => 0555
     child 'readonly',  :mode => 0600
     child 'text',      :mode => 0600, :contents => 'some text to  
start with'
     child 'subdir/'    :mode => 0700 do
       child 'subfile'  :mode => 0555
     end
     child 'bob'        :mode => 0600, :uid => 'bob'
     child 'all'        :mode => 0444

     # Lets define a Pipe resource
     class Pipe < Resource
       # incoming write requests get forwarded to aux object
       def write(fid, offset, data)
         aux.write(data)
       end

       # incoming read requests get forwarded to aux object
       def read(fid, offset, count)
         aux.read(count)
       end
     end

     # Everytime the Device gets instantiated construct
     # a unix domain socketpair, attach the ends to two
     # new Pipe resources and then put the Pipe resources
     # in the device namespace.
     child 'pipe/'      :mode => 0700 do
       data, data1 = *UNIXSocket.socketpair
       child 'data', Pipe, :mode => 0600, :aux => data
       child 'data1', Pipe, :mode => 0600, :aux => data1
     end
   end
end

# Everytime Example is instantiated we'll get a hiearchy like:
#  /readonly
#  /text
#  /subdir
#  /subdir/subfile
#  /bob
#  /all
#  /pipe
#  /pipe/data         data/data1 connected via Unix pipe
#  /pipe/data1

# Access the device via 9P API
device = Example.new
device.version                  # Tversion
a = device.auth                 # Tauth
r = device.attach(a)            # Tattach
data = r.walk('pipe', 'data').open(ORDWR)
data.write('some text')
data1 = r.walk('pipe', 'data1').open
puts data1.read                 # read until EOF (0 byte read)


# Now construct a Plan 9-like namespace for access

ns = NS.attach(Device.new)      # start with memory fs device mounted  
at '/'

ns.mkdir '/d1'
ns.mkdir '/d2'
ns['/d1'].mount Example.new     # instantiate Example and mount
ns['/d2'].mount Example.new     # again but on a different directory

d = ns['/d1/pipe/data'].open(ORDWR)
d.write('some txt')
puts ns['/d1/pipe/data1'].open.read    # read from the other end