linux-kernel - Re: [PATCH] fs: Move attribute flags into non __KERNEL_

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Message-ID: <87vcpfjosl.fsf@linux.vnet.ibm.com>
Date:	Sat, 17 Dec 2011 19:14:26 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Al Viro <viro@...IV.linux.org.uk>,
	Sasha Levin <levinsasha928@...il.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] fs: Move attribute flags into non __KERNEL__ space

On Fri, 16 Dec 2011 23:30:42 +0000, Al Viro <viro@...IV.linux.org.uk> wrote:
> On Fri, Dec 16, 2011 at 11:30:40PM +0200, Sasha Levin wrote:
> > On Fri, 2011-12-16 at 14:23 -0500, Christoph Hellwig wrote:
> > > On Fri, Dec 16, 2011 at 09:47:06AM +0200, Sasha Levin wrote:
> > > > Attribute flags can be useful in userspace when working with filesystems
> > > > such as 9p.
> > > 
> > > No, they aren't.  They are kernel internal values and userspace has no
> > > fucking business messing with them.
> > > 
> > 
> > They became userspace business once they got exposed through 9p.
> > 
> > Take a look at <linux/net/9p/9p.h>:
> > 
> > 	/**
> > 	 * struct p9_iattr_dotl - P9 inode attribute for setattr
> > 	 * @valid: bitfield specifying which fields are valid
> > 	 *         same as in struct iattr
> > 	[...]
> > 
> > That structure is userspace facing, and it's using iattr values.
> > 
> > So either we expose them through fs.h, through 9p.h, or modify 9p code
> > to not use them directly. But claiming that they're kernel internal
> > values isn't entirely correct.
> 
> They *are* kernel internal values and 9P is asking for trouble exposing
> them.  Translation: tomorrow we might reassign those as we bloody wish
> and any userland code that happens to rely on their values will break.
> At which point we'll handle complaints by pointing and laughing.
> 
> It's a 9P bug; fix it there.  Turning random internal constants into a part
> of ABI is not going to work.

I guess we would need to define them at the protocol level then. 
Something like f88657ce3f9713a0c62101dffb0e972a979e77b9. 

-aneesh

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