[git commit master 1/1] Fix resolver broken in NPTL build

[Timo Teräs]

commit: http://git.uclibc.org/uClibc/commit/?id=d6d1bd2bbd2d4445b8e3cb1cb9d8d1aad817ba7f
branch: http://git.uclibc.org/uClibc/commit/?id=refs/heads/master

The combination of

commit aab4df0fb51660300559f5f29290709db2f7bfee
  resolv.c: add support for per thread res_state

commit cca45baf8353d1e338d232f5bdb2d1d6b357f1da
  /etc/resolv.conf: support "timeout:n" and "attempts:n" options

.. and NPTL results in broken resolver in very annoying ways.

Now, it seems that most of the uclibc code does not work well
if res_state is TLS variable. Technically, this is the correct thing
to do since this gives proper per-thread resolving behavior, and
it also makes the config options overridable per thread. This
probably what apps expect as glibc does it too.

But alas, most places use _res to sync up static global variables
which results in breakage. It gets more or less randomly selected
which threads options get applied. Also in case of multiple servers
it looks like the retry logic is shared between all threads, e.g.
two concurrent resolutions can make other resolvers skip nameservers
due to shared "last_ns_num".

And finally the timeout/attempts commit breaks the accumulated stuff
horribly. What happens is:
 1. multithreaded application startups, initializes resolver,
    resolves things just fine
 2. resolv.conf gets changed, application calls res_init
    after res_init uclibc will call res_sync on all resolver functions
    to refresh globals from the TLS variable _res
 3. res_init was called only in one thread, so other thread's
    _res contains all zeroes (yes, this is correct app usage:
    res_init should be called only from one thread)
 4. threads not calling res_init get broken resolver due to timeout
    being set to zero

Now, one proper solution would be to:
 1. make __open_nameservers return the configuration options
 2. pass the config options struct to res_sync_func so it can do
    the proper overrides from per-thread _res
 3. remove the related globals and use locally config options from
    __open_nameservers

But technically, the correct thing (as in glibc does this) is:
 - res_init increases global "res_init timestamp"
 - use _res (or pointer within there) for resolver retries etc.
   get proper per-thread behavior
 - resolvers functions call "maybe_init" which reinitialize the
   TLS'ed resolver state (e.g. reload resolv.conf) if their res_init
   timestamp is out dated

As an immediate emergency kludge fix, the following might do:

resolv: fix options handling for TLS _res

If _res is in TLS (NPTL), it might not get initialized. Assume
zeroes mean default values.

Signed-off-by: Timo Teräs <timo.teras at iki.fi>
Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
---
 libc/inet/resolv.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/libc/inet/resolv.c b/libc/inet/resolv.c
index 831f521..364a4b9 100644
--- a/libc/inet/resolv.c
+++ b/libc/inet/resolv.c
@@ -2892,8 +2892,8 @@ static void res_sync_func(void)
 			__nameserver[n].sa4 = rp->nsaddr_list[n]; /* struct copy */
 #endif
 	}
-	__resolv_timeout = rp->retrans;
-	__resolv_attempts = rp->retry;
+	__resolv_timeout = rp->retrans ? : RES_TIMEOUT;
+	__resolv_attempts = rp->retry ? : RES_DFLRETRY;
 	/* Extend and comment what program is known
 	 * to use which _res.XXX member(s).
 
-- 
1.7.1