linux-kernel - Re: [PATCH -V14 05/11] vfs: Support null pathname in readlink

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Date:	Thu, 8 Jul 2010 03:03:03 +1000
From:	Nick Piggin <npiggin@...e.de>
To:	"Aneesh Kumar K. V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	hch@...radead.org, viro@...iv.linux.org.uk, adilger@....com,
	corbet@....net, serue@...ibm.com, neilb@...e.de,
	hooanon05@...oo.co.jp, bfields@...ldses.org,
	linux-fsdevel@...r.kernel.org, sfrench@...ibm.com,
	philippe.deniel@....FR, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -V14 05/11] vfs: Support null pathname in readlink

On Wed, Jul 07, 2010 at 10:02:12PM +0530, Aneesh Kumar K. V wrote:
> On Thu, 8 Jul 2010 01:27:06 +1000, Nick Piggin <npiggin@...e.de> wrote:
> > This (and all the others) is really ugly overloading of syscall
> > arguments IMO, and the changelog is seriously lacking for such
> > changes.
> 
> Initially we had  freadlink
> 
> http://lkml.org/lkml/2010/5/12/222
> 
> We updated the patches to use the existing readlinkat interface because
> utimensat(2) already exposed a similar interface. So it should be ok to
> expect that other *at call behaved in a similar way ?

I'm not sure whether it's OK or not. Probably is, it is a slight API
change though, that should at least be noted in the changelog.


> > This also changes the the syscall API of existing calls; from reading
> > the path at NULL, to switching to a completely different syscall.
> > Perhaps you're assuming nobody relies on SIGSEGV / mmapped NULL address
> > there, but even then you surely need to document the changed semantics
> > somewhere (and document the new syscall semantics properly).
> 
> 
> Yes this would need a documentation update. But i guess since we already
> have utimensat(2) behaving similarly we are ok to extent readlinkat,
> linkat and faccessat on similar lines ?

At least there is precedent. Pretty ugly though :( Well if others
(Christoph and Al, primarily) think it's OK then fine by me. But
please put comments or changelog for API changes such that a man page
writer could easily update it.


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