linux-kernel - Re: [PATCH v3 1/1] dcache: Translating dentry into pathname without taking rename

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Message-ID: <20130908045814.GG13318@ZenIV.linux.org.uk>
Date:	Sun, 8 Sep 2013 05:58:14 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Ian Kent <raven@...maw.net>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Waiman Long <Waiman.Long@...com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>,
	George Spelvin <linux@...izon.com>,
	John Stoffel <john@...ffel.org>, Sage Weil <sage@...tank.com>
Subject: Re: [PATCH v3 1/1] dcache: Translating dentry into pathname without
 taking rename_lock

On Sun, Sep 08, 2013 at 12:15:46PM +0800, Ian Kent wrote:
> > and *name is never modified in it.  Why not simply pass it by value?
> > Moreover, I'm not sure I understand what do we need sbi->fs_lock in
> > there.  Other than that, it's very close to dentry_path() (well, that
> > and different calling conventions).  Ian?
> 
> Yes, it is close to dentry_path() but the path functions used to return
> the full path to the root, although I don't see where dentry_path() get
> the root, mmm ... 

dentry_path(), unlike d_path(), is relative to the root of filesystem
containing dentry in question.  There are 3 of those suckers:
	d_path(): vfsmount/dentry => path to current process' root
	d_absolute_path(): ditto, but ignores chroot jails (goes to
the absolute root of namespace)
	dentry_path(): dentry => path from root of fs containing that
dentry.

IOW, if you have something mounted on /jail/mnt/foo and are chrooted into
/jail, passing vfsmount/dentry of /jail/mnt/foo/bar/baz to d_path() will
yield "/mnt/foo/bar/baz", to d_absolute_path() - "/jail/mnt/foo/bar/baz" and
passing the same dentry to dentry_path() - "/bar/baz".
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