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Message-ID: <4B7A9852.5020105@redhat.com>
Date: Tue, 16 Feb 2010 21:06:26 +0800
From: Cong Wang <amwang@...hat.com>
To: Octavian Purdila <opurdila@...acom.com>
CC: David Miller <davem@...emloft.net>,
Linux Kernel Network Developers <netdev@...r.kernel.org>,
Linux Kernel Developers <linux-kernel@...r.kernel.org>,
Neil Horman <nhorman@...driver.com>,
Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [net-next PATCH v4 3/3] net: reserve ports for applications using
fixed port numbers
Octavian Purdila wrote:
> On Tuesday 16 February 2010 11:37:04 you wrote:
>>> BUILD_BUG_ON(sizeof(struct inet_skb_parm) > sizeof(dummy_skb->cb));
>>>
>>> + sysctl_local_reserved_ports = kzalloc(65536 / 8, GFP_KERNEL);
>>> + if (!sysctl_local_reserved_ports)
>>> + goto out;
>>> +
>> I think we should also consider the ports in ip_local_port_range,
>> since we can only reserve the ports in that range.
>>
>
> That is subject to changes at runtime, which means we will have to readjust
> the bitmap at runtime which introduces the need for additional synchronization
> operations which I would rather avoid.
Why? As long as the bitmap is global, this will not be hard.
Consider that if one user writes a port number which is beyond
the ip_local_port_range into ip_local_reserved_ports, we should
not accept this, because it doesn't make any sense. But with your
patch, we do.
>
>>> + {
>>> + .procname = "ip_local_reserved_ports",
>>> + .data = NULL, /* initialized in sysctl_ipv4_init */
>>> + .maxlen = 65536,
>>> + .mode = 0644,
>>> + .proc_handler = proc_dobitmap,
>>> + },
>> Isn't there an off-by-one here?
>>
>> In patch 2/3, you use 0 to set the fist bit, then how about 65535 which
>> writes 65536th bit? This is beyond the range of port number.
>>
>
> This seems fine to me, 65535 is the value used by both the port checking
> function and the proc read/write function. And it translates indeed to
> 65536th bit, but that is also bit 65535 if you start counting bits from 0
> instead of 1. The usual computing/natural arithmetic confusion for the meaning
> of first :)
>
Oh, I see.
Thanks.
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