On 16/04/2012 16:48, Rich Felker wrote:
On Mon, Apr 16, 2012 at 03:05:54PM +0100, Ed W wrote:
Hi, I'm suffering extreme performance problems with getaddrinfo
being used by ipset to do conversions from IP textual strings to
number. Although the IP address is textual there is a reverse DNS
lookup performed and in the event that my resolver is slow, this is
sometimes taking 60seconds or so to return
I have not looked at the source, but I suspect this is a uClibc bug
based on a misreading of the standard. Many incorrect historical
getaddrinfo implementations performed unnecessary reverse dns lookups
to fill in the ai_canonname field of the addrinfo structure. POSIX is
very clear that this is wrong:
A numeric host address string is not a ``name'', and thus does not
have a ``canonical name'' form; no address to host name translation
is performed. See below for handling of the case where a canonical
name cannot be obtained.
Source:
http://pubs.opengroup.org/onlinepubs/9699919799/functions/getaddrinfo.html
I have traced it to gethostbyaddr_r in resolv.c. This function calls
__dns_lookup recursively
Should we ever be calling dns in here?
Ed
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