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From: reader@×××××××.com |
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Subject: [gentoo-user] Re: OT: How to check for an existing ethernet link ? |
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Date: Sun, 01 Oct 2006 10:27:34 -0500 |
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> Meino Christian Cramer <Meino.Cramer@×××.de> writes: |
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> |
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> > Hi, |
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> > |
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> > sorry for being off topic, but I think, folks of this list have the |
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> > knowledge to answer my question and I have no idea who to ask else... |
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> > |
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> > I need to check from within a C-program whether the computer, the |
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> > program is running on (OS: Linux), is connected to the ethernet. The |
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> > program is running under root privilege. Before doing anything else |
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> > with eth0, I want to check the link-LED of the ethernet card...so to |
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> > say. |
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> > |
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> > I sthere any "legal" way to do such things under Linux? |
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> |
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> A common way is to use the result of a single ping to known up host, |
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> in an if/else control block. |
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> |
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> -- |
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> gentoo-user@g.o mailing list |
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> |
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The problem is a little different here. In principle ping'ing is a |
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good way to test the availablity of a net-connection. No doubt! |
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But in my case I have to avoid *ANY* timeouts (wayting for an answer |
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or another timeout for example: the timeout of "gethostbyname()") if |
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possible. My program has to react AS FAST AS POSSIBLE on error |
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conditions. So if I can check the availability of a net-connection |
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without actually accessing the net and wait for an answer (or an error |
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condition) it would be the best solution. The fact that I am urged to |
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use UDP makes things even more difficult. I know that simply |
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attaching the computer to a switch/hub and removing the net-plug there |
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makes the link check worthless ... but I want to try every possibility |
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to find out, whether there is the chance to contact the "target" |
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(wrong word...sorry) without trying exactly that (or similiar), |
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haveing to wait for an answer (or error condition) and paying the |
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panalty of timeouts then. |
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If there is any net-programming hyper-guru out there who knows some |
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special tricks to achieve the shortest possible time of |
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reaction...here is someone who will thank her/him very much for any |
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help in advance ! :) |
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keep hacking! |
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mcc |
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|
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-- |
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