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Date: Mon, 16 Jul 2007 05:47:46 -0400
From: Jeff Garzik <jeff@garzik.org>
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To: "H. Peter Anvin" <hpa@zytor.com>
CC: Miklos Szeredi <miklos@szeredi.hu>, jeremy@goop.org,
       jengelh@computergmbh.de, viro@ftp.linux.org.uk, nmiell@comcast.net,
       linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: *at syscalls for xattrs?
References: <Pine.LNX.4.64.0707132228460.25352@fbirervta.pbzchgretzou.qr> <20070715205313.GE21668@ftp.linux.org.uk> <1184534001.2765.5.camel@entropy> <20070715222323.GG21668@ftp.linux.org.uk> <Pine.LNX.4.64.0707160954160.25352@fbirervta.pbzchgretzou.qr> <469B2CAE.9010101@goop.org> <E1IAMWA-0004fM-00@dorka.pomaz.szeredi.hu> <469B3B73.9010400@zytor.com>
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H. Peter Anvin wrote:
> Miklos Szeredi wrote:
>> The *at() thing basically gives you the advantages of a CWD without
>> the disadvantages.
>>
>> For example it could be useful to implement the functionality of
>> find(1) as a library interface.
>>
> 
> What the *at() interfaces really do is fix/paper over a longstanding
> wart in Unix: the cwd really should have been a standard file descriptor
> (like stdin/stdout/stderr) instead of a magic piece of state maintained
> in kernel space.

It's more than a wart, IMO.  *at() allows one to close races (with 
potential security implications) that are otherwise impossible to close, 
in directory traversal.

*at() permits a userspace program to hold proper references to all 
objects during a directory traversal, with all that implies.

	Jeff