linux-kernel - Re: *at syscalls for xattrs?

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Message-ID: <469B3EC2.8080702@garzik.org>
Date:	Mon, 16 Jul 2007 05:47:46 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Miklos Szeredi <miklos@...redi.hu>, jeremy@...p.org,
	jengelh@...putergmbh.de, viro@....linux.org.uk, nmiell@...cast.net,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: *at syscalls for xattrs?

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



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