linux-kernel - Re: [patch 7/8] fdmap v2

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Message-ID: <alpine.LFD.0.98.0706092159110.20321@woody.linux-foundation.org>
Date:	Sat, 9 Jun 2007 22:06:27 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	dean gaudet <dean@...tic.org>
cc:	Al Viro <viro@....linux.org.uk>,
	Kyle Moffett <mrmacman_g4@....com>,
	Ulrich Drepper <drepper@...hat.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Theodore Tso <tytso@....edu>,
	Eric Dumazet <dada1@...mosbay.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [patch 7/8] fdmap v2 - implement sys_socket2

On Sat, 9 Jun 2007, dean gaudet wrote:
> 
> for an example of a library wanting to cache an open fd ... and failing 
> miserably at protecting itself from the application closing its fd read:

Heh.

Why the hell doesn't that thing just do an "fstat()" on the thing, and 
compare the inode number? Not that I would guarantee that it works either 
for a socket, but it would seem to make more sense than what it apparently 
does now, and I think it should work at least on Linux.

(Ie linux will give fake "st_ino" numbers to sockets. Whether anybody else 
will do that, I have no friggin clue. And you probably shouldn't depend on 
it even under Linux, but damn, despite all of those issues, it's likely 
better and more logical than what libnss-ldap apparently does now ;)

Doing a "fstat()" call is how you generally test if two fd's point to the 
same file. Doing the same thing for sockets would at least be half-way 
sane, and even if the OS doesn't give new sockets individual st_ino 
numbers, they probably won't be *changing*.

		Linus
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