[Gllug] Network traffic

[Bruce Richardson]

On Tue, Nov 27, 2001 at 06:31:36PM +0000, Dylan Brewis wrote:
> >
> > Tet
> I can't accept that explanation of how cp (etc.) operate (although I can see 
> that the operation may cause the traffic as the software may be 'dumb' to 
> that extent.). surely:
> 
> cp calls an api/kernel function/procedure/whatever to request or return the 
> data.
> The called routine passes the request/data to the relevant filesystem module 
> to actually perform the file get or put.
> 
> Otherwise, cp would still need to know how to access any type of fs, and a 
> new fs type would require a new version on cp to support it. I thought that 
> was the point of modules (and api's, operating systems in general.)

Filesystem modules make the contents of a file-system accessible to the
Virtual File System.  They don't provide higher level functions nor is
there a local file-server daemon, so copying a file is a high-level,
user-space process.  Creating, opening, reading, writing files,
reading/changing their status - those are the low-level filesystem
tasks.  Other actions are left to a higher level.  This is modularity.

Given that, for your remote-procedure example to work cp would have to
detect network file systems so that it could send a remote command where
approprate but do the work itself for local systems.

AFAIK, only some network filesystem provides remote calls for fast file
copying.  Netware does and if you install the ncpfs tools there's an
ncopy tool that takes advantage of it.

Filesystem modules do quite a lot, especially the ones which make remote
and/or non-unix filesystems appear to be a local *nix filesystem.  But
making the fs transparently accessible is the goal.  Higher level
functions are implemented by the accompanying fs suites or by you, the
coder.

-- 
Bruce

It is impolite to tell a man who is carrying you on his shoulders that
his head smells.
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