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From: Al Viro <viro@ZenIV.linux.org.uk>
Subject: Re: [take 3] pohmelfs: call for inclusion
Date: Wed, 21 Mar 2012 22:28:12 +0000
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Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Joe Perches <joe@perches.com>, greg@kroah.com,
	linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
	linux-fsdevel@vger.kernel.org,
	Stephen Rothwell <sfr@canb.auug.org.au>
To: Evgeniy Polyakov <zbr@ioremap.net>
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On Thu, Mar 22, 2012 at 02:04:15AM +0400, Evgeniy Polyakov wrote:

> Details are pretty simple - we want to allow external applications to
> get to filesystem and grab data via single requests, since it is
> stateless and can not hold dentry structure. They do not connect to
> server which runs on top of filesystem, but insted directly to storage,
> which hosts raw data.
> 
> Applications know they uploadede data via /whatever/path/was/to/the/file
> And they want to get that data from server via single 'get'. Obviously
> they can not store mapping from all filenames to inode number, and they
> can not request dozen of directory lookups, since it takes time and has
> to maintain state.

Sigh... I wish it hadn't been an English-speaking maillist; mat is hard to
translate properly...

OK, let me try for a printable version: suppose we replace that d_path()
call with dentry_path() and leave everything else as is; what exactly
will be broken and how will it break?

> When object was written via remounted path, then it is a problem for
> those who made a setup - this ugly hack only 'works' in specially
> crafted environment, which provides its pros and requires fair price of
> cons.

_What_ remounted path?  I'm not talking about bindings at all...