linux-ext4 - Re: [PATCH 0/6] Extended file stat system call

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Date:	Fri, 27 Apr 2012 00:33:06 +0000
From:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
To:	Roland McGrath <roland@...k.frob.com>
CC:	David Howells <dhowells@...hat.com>,
	Steve French <smfrench@...il.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"linux-cifs@...r.kernel.org" <linux-cifs@...r.kernel.org>,
	"samba-technical@...ts.samba.org" <samba-technical@...ts.samba.org>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"wine-devel@...ehq.org" <wine-devel@...ehq.org>,
	"kfm-devel@....org" <kfm-devel@....org>,
	"nautilus-list@...me.org" <nautilus-list@...me.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
	"libc-alpha@...rceware.org" <libc-alpha@...rceware.org>
Subject: Re: [PATCH 0/6] Extended file stat system call

On Thu, 2012-04-26 at 15:05 -0700, Roland McGrath wrote:
> > What if the xstat() and struct xstat eventually becomes what userspace
> > uses as stat() (as a wrapper) and struct stat (if such a thing is
> > possible with glibc versioning)?  
> 
> It's certainly possible with symbol versioning, though it seems much more
> likely that we'd stick with the existing struct stat and stat* interfaces
> and only have the implementation using statx underneath (e.g. for new
> machines or kernel ABIs where the kernel stops providing any calls except
> for statxat), at least for the foreseeable future.
> 
> > Do older programs that think they're using stat() and don't know about
> > the extra fields available expect to see a useful value in st_ino?
> 
> POSIX requires that st_ino have a useful value for the standard *stat calls.

Yes, but we're talking about non-POSIX filesystems here. If the
filesystem doesn't have a useful value for st_ino, then the usual way of
dealing with those POSIX requirements is to fake up values. The question
then becomes whether or not we care if it is the kernel or userland that
fakes up those values.

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@...app.com
www.netapp.com