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
OK, attached is my patch which implements posix defined behaviour,
including returning an error condition if we hint AI_NUMERICSERV and it
isn't
Grateful if someone could look it over and apply if it seems fine?
Main change is that DNS lookups will not be triggered for a bunch of
unnecessary situations. This can be a big performance increase in
certain cases
Thanks
Ed W
Posix says that we should not do reverse dns lookups in getaddrinfo
to populate canonname.
See: http://pubs.opengroup.org/onlinepubs/9699919799/functions/getaddrinfo.html
Signed-off-by: Ed Wildgoose <[email protected]>
---
--- a/libc/inet/getaddrinfo.c 2012-04-16 18:28:05.000000000 +0100
+++ b/libc/inet/getaddrinfo.c 2012-04-16 18:28:30.000000000 +0100
@@ -628,13 +628,18 @@
char
buffer[sizeof("ffff:ffff:ffff:ffff:ffff:ffff:255.255.255.255")];
while (at2 != NULL) {
- if (req->ai_flags & AI_CANONNAME) {
+ if ( (req->ai_flags & AI_CANONNAME)
+ && !inet_ntop(at2->family, at2->addr, buffer, sizeof(buffer))
) {
struct hostent *h = NULL;
int herrno;
struct hostent th;
size_t tmpbuflen = 512;
char *tmpbuf;
+ /* Hint says numeric, but address is not */
+ if (req->ai_flags & AI_NUMERICSERV)
+ return -EAI_NONAME;
+
do {
tmpbuflen *= 2;
tmpbuf = alloca(tmpbuflen);
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