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
Rich
Rich, disregarding posix for a moment, what does glibc do? Options are:
canonname=NULL or IP as string?
At present uclibc is returning the reverse dns lookup or textual IP
format. It should be trivial for me to supply a patch to make this
whatever we want - can someone define what we want? (Posix or emulate
some other wierdness?)
Just to be clear - my understanding is (for posix)
if ( inet_pton(addr) )
canonname = NULL;
else
canonname = reverse_dns;
Therefore we don't need to examine AI_NUMERICHOST and will return
canonname=NULL for any case of an IP addr?
(We should of course return an error if the user hints AI_NUMERICHOST
and it's not numeric)
Grateful for confirm this is the implementation we want?
Ed W
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