linux-kernel - Re: [PATCH] namei: revert old behaviour for filename_lookup with LOOKUP

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Message-ID: <20161013212404.GU19539@ZenIV.linux.org.uk>
Date:   Thu, 13 Oct 2016 22:24:04 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Vineeth Remanan Pillai <vineethp@...zon.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        kamatam@...zon.com, aliguori@...zon.com
Subject: Re: [PATCH] namei: revert old behaviour for filename_lookup with
 LOOKUP_PARENT flag

On Thu, Oct 13, 2016 at 01:41:11PM -0700, Vineeth Remanan Pillai wrote:

> Yes, the use case is out-of-tree and the code snippet above depicts the use
> .
> Since kern_path_locked is also not exported, out-of-tree code used kern_path
> for the existence check for directories.
> 
> One reference about this issue can be seen here.
> 
> http://www.gossamer-threads.com/lists/linux/kernel/2459690?do=post_view_flat#2459690

... and in that thread I have asked for details and got no reply whatsoever.

> We also have a customer who complained about this functionality change.
> 
> I understand that there has been no API promises been made to this API. But
> since this is an
> exported function, the change in function could cause break in out-of-tree
> kernel code. I will
> rephrase the commit message to say "change in functionality" instead of
> regression

In principle, I have no strong objections against exporting kern_path_locked,
provided it really matches what they (whoever they are) need.  I'm still
curious about the context, though - what is that code trying to do?  Depending
on the actual stuff it wants to implement, there might be better primitives
for doing that *and* there might be something worth adding and exporting
that would be a better match.

It's not that kern_path_locked() isn't a sane interface, but... using it
might be a sign of trying to work around something missing in API.  So again,
please post more details.