linux-kernel - Re: [RFC] ->get_link(), ->put

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Message-ID: <20160103202121.GM9938@ZenIV.linux.org.uk>
Date:	Sun, 3 Jan 2016 20:21:21 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [RFC] ->get_link(), ->put_link() and cookies

On Sun, Jan 03, 2016 at 11:53:21AM -0800, Linus Torvalds wrote:
> On Thu, Dec 31, 2015 at 10:36 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> >         In cases when we need to pin the symlink body in some manner, we
> > need to undo whatever we'd done once the caller is done with the body.
> > That went through several variants, the latest (in -next right now) being
> > "have non-NULL ->put_link() and leave an argument for it in void *cookie,
> > address of which is passed to ->get_link()".
> 
> The series looks ok to me, even if I still am not a fan of the cookie.
> I suspect the remaining users could easily embed the returned string
> at the end of a structure, and get their data with container_of(). It
> would complicate their unusual behavior for sure, but make the common
> case much more understandable.
> 
> Oh well. I won't insist - it may be too painful to be worth it. And
> it's a fairly separate issue anyway.
> 
> So no objections to this series.

Just to make sure - that does include 13/13, presumably?  IOW, ->put_link()
is gone and the final calling conventions for ->get_link() are
	const char *(*get_link)(struct dentry *dentry,
				struct inode *inode,
				struct delayed_call *done);
with dentry == NULL <=> call in RCU mode, ERR_PTR(-E...) returned on error
and set_delayed_call(done, destructor, arg) done if destructor(arg) should
be done once pathname resolution is through with the body returned by
->get_link().
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