linux-kernel - Re: [PATCH] VFS: new fgetattr() file operation

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Message-ID: <20071025235206.GA995458@sgi.com>
Date:	Fri, 26 Oct 2007 09:52:06 +1000
From:	David Chinner <dgc@....com>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	dgc@....com, staubach@...hat.com, akpm@...ux-foundation.org,
	hch@...radead.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] VFS: new fgetattr() file operation

On Fri, Oct 26, 2007 at 01:10:14AM +0200, Miklos Szeredi wrote:
> > On Wed, Oct 24, 2007 at 05:27:04PM +0200, Miklos Szeredi wrote:
> > > > >> Wouldn't you be better off by attempting to implement an "open
> > > > >> by ino" operation and an operation to get the generation count
> > > > >> for the file and then modifying the network protocol of interest
> > > > >> to use these as identifiers for the file to be manipulated?
> > > > >>     
> > > > >
> > > > > You mean an "open by inode" on the userspace API?  My guess, it
> > > > > wouldn't get very far.
> > > > 
> > > > This isn't a new idea and has been implemented on a variety of
> > > > different systems.
> > > 
> > > Like?
> > 
> > XFS.
> > 
> > 'man open_by_handle'
> 
> Doesn't seem widely used, with 600 something google hits.

from the man page:

"They are intended  for  use  by a limited set of system utilities such
as backup programs."

It also gets used by HSMs and so it is current, tested and is not
going away....

> And in this
> old thread Linus is not entirely enthusiastic about the concept:
> 
>   http://lkml.org/lkml/1999/1/11/244

That was "open by inode number", AFAICT. A handle is an opaque
blob that can be an arbitrary length defined by the filesystem.
You have to convert a fd or path to a handle first before you can
use it later, so any filesystem can implement it...

i.e. it is exactly what this (unanswered) post suggested:

http://lkml.org/lkml/1999/1/13/186

Just my 2c worth....

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group
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