call gethostbyname() after device reacquires IP address
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From: Marco Wang on 14 Mar 2007 11:23 Hello, I am working on writing code for a networking device. The device is linux based. Now I encounter a problem: 1. The device is powered on and application started, but network cable is unplugged; 2. Application on device calls gethostbyname() or something like that to get IP address; 3. As network cable is unplugged, the device failed to acquire DHCP IP address (including DNS info); 4. So gethostbyname() failed to resolve remote host name; 5. Plug network cable into device, the device will get IP/DNS info sooner or later; 6. But gethostbyname() still won't work unless the process is restarted; I know gethostbyname() retrieves host/network info only once when it is invoked the first time, so I use res_init() to solve this issue, then gethostbyname() will return correct information, but it takes too long: around 30 seconds. Anyone has any idea why such 30 seconds occurs? TIA. Thanks, Marco Wang
From: Rick Jones on 14 Mar 2007 14:38
It isn't really an answer to your question, but new code really should be using getaddrinfo() rather than gethostbyname(). As for the rest of it, perhaps some system call tracing would help - run your application under strace and look at the system calls being made - that may help tell you want is going-on/wrong. If I were to guess, it would be that gethostbyname() and the resolver libraries were caching bogus DNS server information - if DHCP didn't provide an IP address to the NIC, it likely didn't provide DNS server information to go into /etc/resolv.conf either. rick jones -- a wide gulf separates "what if" from "if only" these opinions are mine, all mine; HP might not want them anyway... :) feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH... |