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Implement second fallback mode for DNS requests. 

There is some more shardware/software out there which has problems
if two DNS requests are sent using the same tuple

  (source addr, source port, dest addr, dest port)

This can range from firewalls to load balancers.  Some of the vendors
already fixed it in response to this problem.  Still, we need a way
to make glibc work with broken environments.  The single-request-reopen
flag can be used or we fall back automatically to this mode.
This commit is contained in:
Ulrich Drepper 2009-06-26 03:47:47 -07:00
parent 54c99aabdb
commit 44d20bca52
4 changed files with 65 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
ChangeLog
View File

@ -1,3 +1,14 @@
2009-06-26 Ulrich Drepper <drepper@redhat.com>
* resolv/resolv.h: Define RES_SNGLKUPREOP.
* resolv/res_init.c (res_setoptions): Recognize single-request-reopen
option.
* resolv/res_send.c (reopen): New function. Broken out of...
(send_dg): ... here. Recognize RES_SNGLKUPREOP. Implement second
fallback mechanism. If single-request fails switch to
single-request-reopen mode which opens a new socket for the second
request.
2009-06-25 Andreas Schwab <aschwab@redhat.com>
* sysdeps/powerpc/powerpc32/____longjmp_chk.S (LOAD_ARG): Define.

3
resolv/res_init.c
View File

@ -540,6 +540,9 @@ res_setoptions(res_state statp, const char *options, const char *source) {
statp->options |= RES_NOCHECKNAME;
} else if (!strncmp(cp, "edns0", sizeof("edns0") - 1)) {
statp->options |= RES_USE_EDNS0;
} else if (!strncmp(cp, "single-request-reopen",
sizeof("single-request-reopen") - 1)) {
statp->options |= RES_SNGLKUPREOP;
} else if (!strncmp(cp, "single-request",
sizeof("single-request") - 1)) {
statp->options |= RES_SNGLKUP;

68
resolv/res_send.c
View File

@ -908,24 +908,11 @@ send_vc(res_state statp,
}
static int
send_dg(res_state statp,
const u_char *buf, int buflen, const u_char *buf2, int buflen2,
u_char **ansp, int *anssizp,
int *terrno, int ns, int *v_circuit, int *gotsomewhere, u_char **anscp,
u_char **ansp2, int *anssizp2, int *resplen2)
reopen (res_state statp, int *terrno, int ns)
{
const HEADER *hp = (HEADER *) buf;
const HEADER *hp2 = (HEADER *) buf2;
u_char *ans = *ansp;
int orig_anssizp = *anssizp;
struct sockaddr_in6 *nsap = EXT(statp).nsaddrs[ns];
struct timespec now, timeout, finish;
struct pollfd pfd[1];
int ptimeout;
struct sockaddr_in6 from;
int resplen, n;
if (EXT(statp).nssocks[ns] == -1) {
struct sockaddr_in6 *nsap = EXT(statp).nsaddrs[ns];
/* only try IPv6 if IPv6 NS and if not failed before */
if ((EXT(statp).nscount6 > 0) && !statp->ipv6_unavail) {
if (__builtin_expect (__have_o_nonblock >= 0, 1)) {
@ -1000,6 +987,26 @@ send_dg(res_state statp,
}
}
return 1;
}
static int
send_dg(res_state statp,
const u_char *buf, int buflen, const u_char *buf2, int buflen2,
u_char **ansp, int *anssizp,
int *terrno, int ns, int *v_circuit, int *gotsomewhere, u_char **anscp,
u_char **ansp2, int *anssizp2, int *resplen2)
{
const HEADER *hp = (HEADER *) buf;
const HEADER *hp2 = (HEADER *) buf2;
u_char *ans = *ansp;
int orig_anssizp = *anssizp;
struct timespec now, timeout, finish;
struct pollfd pfd[1];
int ptimeout;
struct sockaddr_in6 from;
int resplen, n;
/*
* Compute time for the total operation.
*/
@ -1008,8 +1015,15 @@ send_dg(res_state statp,
seconds /= statp->nscount;
if (seconds <= 0)
seconds = 1;
bool single_request = (statp->options & RES_SNGLKUP) != 0;// XXX
bool single_request = (statp->options & RES_SNGLKUP) != 0;
bool single_request_reopen = (statp->options & RES_SNGLKUPREOP) != 0;
int save_gotsomewhere = *gotsomewhere;
int retval;
retry_reopen:
retval = reopen (statp, terrno, ns);
if (retval <= 0)
return retval;
retry:
evNowTime(&now);
evConsTime(&timeout, seconds, 0);
@ -1064,6 +1078,14 @@ send_dg(res_state statp,
*gotsomewhere = save_gotsomewhere;
goto retry;
}
else if (!single_request_reopen)
{
statp->options |= RES_SNGLKUPREOP;
single_request_reopen = true;
*gotsomewhere = save_gotsomewhere;
__res_iclose (statp, false);
goto retry_reopen;
}
*resplen2 = 1;
return resplen;
@ -1092,7 +1114,8 @@ send_dg(res_state statp,
Perror(statp, stderr, "send", errno);
goto err_out;
}
if (nwritten != 0 || buf2 == NULL || single_request)
if (nwritten != 0 || buf2 == NULL
|| single_request || single_request_reopen)
pfd[0].events = POLLIN;
else
pfd[0].events = POLLIN | POLLOUT;
@ -1306,8 +1329,15 @@ send_dg(res_state statp,
recvresp2 = 1;
/* Repeat waiting if we have a second answer to arrive. */
if ((recvresp1 & recvresp2) == 0) {
if (single_request)
if (single_request || single_request_reopen) {
pfd[0].events = POLLOUT;
if (single_request_reopen) {
__res_iclose (statp, false);
retval = reopen (statp, terrno, ns);
if (retval <= 0)
return retval;
}
}
goto wait;
}
/*

2
resolv/resolv.h
View File

@ -216,6 +216,8 @@ struct res_sym {
reverse lookup */
#define RES_USE_EDNS0 0x00100000 /* Use EDNS0. */
#define RES_SNGLKUP 0x00200000 /* one outstanding request at a time */
#define RES_SNGLKUPREOP 0x00400000 /* -"-, but open new socket for each
request */
#define RES_DEFAULT (RES_RECURSE|RES_DEFNAMES|RES_DNSRCH|RES_NOIP6DOTINT)