netdev - Re: [Bug 106241] New: shutdown(3)/close(3) behaviour is incorrect for sockets in accept(3)

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Date:	Fri, 23 Oct 2015 15:20:35 +0200
From:	Casper.Dik@...cle.com
To:	Eric Dumazet <eric.dumazet@...il.com>
cc:	Al Viro <viro@...IV.linux.org.uk>,
	Alan Burlison <Alan.Burlison@...cle.com>,
	David Miller <davem@...emloft.net>, stephen@...workplumber.org,
	netdev@...r.kernel.org, dholland-tech@...bsd.org
Subject: Re: [Bug 106241] New: shutdown(3)/close(3) behaviour is incorrect for sockets in accept(3) 



>Yet another POSIX deficiency.
>
>When a server deals with 10,000,000+ socks, we absolutely do not care of
>this requirement.
>
>O(log(n)) is still crazy if it involves O(log(n)) cache misses.

You miss the fire point of the algorithm; you *always* find an available 
file descriptor in O(log(N)) (where N is the size of the table).

Does your algorithm guarantee that?

>> Is it a problem that you can "hide" your listening socket with a thread in 
>> accept()?  I would think so (It would be visible in netstat but you can't 
>> easily find out why has it)
>
>Again, netstat -p on a server with 10,000,000 sockets never completes.

This point was not about a 10M sockets server but in general...

>Never try this unless you are desperate and want to avoid a reboot
>maybe.
>
>If you absolutely want to nuke a listener because of untrusted
>applications, we better implement a proper syscall.
>
>Android has such a facility.

Solaris has had such an option too, but that wasn't the point.  You really 
don't want to know which application is doing this?

>Alternative would be to extend netlink (ss command from iproute2
>package) to carry one pid per socket.
>
>ss -atnp state listening

That would be an option too.

Casper


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