glibc/resolv
Joseph Myers a5f891ac8d Consistently include Makeconfig after defining subdir.
In <https://sourceware.org/ml/libc-alpha/2014-01/msg00196.html> I
noted it was necessary to add includes of Makeconfig early in various
subdirectory makefiles for the tests-special variable settings added
by that patch to be conditional on configuration information.  No-one
commented on the general question there of whether Makeconfig should
always be included immediately after the definition of subdir.

This patch implements that early inclusion of Makeconfig in each
directory (which is a lot easier than consistent placement of includes
of Rules).  Includes are added if needed, or moved up if already
present.  Subdirectory "all:" targets are removed, since Makeconfig
provides one.

There is potential for further cleanups I haven't done.  Rules and
Makerules have code such as

ifneq   "$(findstring env,$(origin headers))" ""
headers :=
endif

to override to empty any value of various variables that came from the
environment.  I think there is a case for Makeconfig setting all the
subdirectory variables (other than subdir) to empty to ensure no
outside value is going to take effect if a subdirectory fails to
define a variable.  (A list of such variables, possibly out of date
and incomplete, is in manual/maint.texi.)  Rules and Makerules would
give errors if Makeconfig hadn't already been included, instead of
including it themselves.  The special code to override values coming
from the environment would then be obsolete and could be removed.

Tested x86_64, including that installed binaries are identical before
and after the patch.

	* argp/Makefile: Include Makeconfig immediately after defining
	subdir.
	* assert/Makefile: Likewise.
	* benchtests/Makefile: Likewise.
	* catgets/Makefile: Likewise.
	* conform/Makefile: Likewise.
	* crypt/Makefile: Likewise.
	* csu/Makefile: Likewise.
	(all): Remove target.
	* ctype/Makefile: Include Makeconfig immediately after defining
	subdir.
	* debug/Makefile: Likewise.
	* dirent/Makefile: Likewise.
	* dlfcn/Makefile: Likewise.
	* gmon/Makefile: Likewise.
	* gnulib/Makefile: Likewise.
	* grp/Makefile: Likewise.
	* gshadow/Makefile: Likewise.
	* hesiod/Makefile: Likewise.
	* hurd/Makefile: Likewise.
	(all): Remove target.
	* iconvdata/Makefile: Include Makeconfig immediately after
	defining subdir.
	* inet/Makefile: Likewise.
	* intl/Makefile: Likewise.
	* io/Makefile: Likewise.
	* libio/Makefile: Likewise.
	(all): Remove target.
	* locale/Makefile: Include Makeconfig immediately after defining
	subdir.
	* login/Makefile: Likewise.
	* mach/Makefile: Likewise.
	(all): Remove target.
	* malloc/Makefile: Include Makeconfig immediately after defining
	subdir.
	(all): Remove target.
	* manual/Makefile: Include Makeconfig immediately after defining
	subdir.
	* math/Makefile: Likewise.
	* misc/Makefile: Likewise.
	* nis/Makefile: Likewise.
	* nss/Makefile: Likewise.
	* po/Makefile: Likewise.
	(all): Remove target.
	* posix/Makefile: Include Makeconfig immediately after defining
	subdir.
	* pwd/Makefile: Likewise.
	* resolv/Makefile: Likewise.
	* resource/Makefile: Likewise.
	* rt/Makefile: Likewise.
	* setjmp/Makefile: Likewise.
	* shadow/Makefile: Likewise.
	* signal/Makefile: Likewise.
	* socket/Makefile: Likewise.
	* soft-fp/Makefile: Likewise.
	* stdio-common/Makefile: Likewise.
	* stdlib/Makefile: Likewise.
	* streams/Makefile: Likewise.
	* string/Makefile: Likewise.
	* sunrpc/Makefile: Likewise.
	(all): Remove target.
	* sysvipc/Makefile: Include Makeconfig immediately after defining
	subdir.
	* termios/Makefile: Likewise.
	* time/Makefile: Likewise.
	* timezone/Makefile: Likewise.
	(all): Remove target.
	* wcsmbs/Makefile: Include Makeconfig immediately after defining
	subdir.
	* wctype/Makefile: Likewise.

libidn/ChangeLog:
	* Makefile: Include Makeconfig immediately after defining subdir.

localedata/ChangeLog:
	* Makefile: Include Makeconfig immediately after defining subdir.
	(all): Remove target.

nptl/ChangeLog:
	* Makefile: Include Makeconfig immediately after defining subdir.

nptl_db/ChangeLog:
	* Makefile: Include Makeconfig immediately after defining subdir.
2014-02-26 23:12:03 +00:00
..
arpa Avoid use of "register" as optimization hint. 2013-06-07 22:24:35 +00:00
nss_dns Properly fix memory leak in _nss_dns_gethostbyname4_r with big DNS answer 2014-02-19 14:39:21 +01:00
sys initial import 1995-02-18 01:27:10 +00:00
Banner Update. 2000-07-19 22:03:58 +00:00
base64.c Update. 2004-10-18 05:10:37 +00:00
Depend * manual/install.texi (Installation): Don't mention linuxthreads. 2005-07-03 04:40:53 +00:00
ga_test.c Update. 2001-03-03 18:21:04 +00:00
gai_cancel.c Update copyright notices with scripts/update-copyrights 2014-01-01 22:00:23 +10:00
gai_error.c Update copyright notices with scripts/update-copyrights 2014-01-01 22:00:23 +10:00
gai_misc.c Update copyright notices with scripts/update-copyrights 2014-01-01 22:00:23 +10:00
gai_misc.h Update copyright notices with scripts/update-copyrights 2014-01-01 22:00:23 +10:00
gai_notify.c Update copyright notices with scripts/update-copyrights 2014-01-01 22:00:23 +10:00
gai_sigqueue.c Update copyright notices with scripts/update-copyrights 2014-01-01 22:00:23 +10:00
gai_suspend.c Update copyright notices with scripts/update-copyrights 2014-01-01 22:00:23 +10:00
getaddrinfo_a.c Update copyright notices with scripts/update-copyrights 2014-01-01 22:00:23 +10:00
gethnamaddr.c Properly fix memory leak in _nss_dns_gethostbyname4_r with big DNS answer 2014-02-19 14:39:21 +01:00
herror.c * posix/tst-execle1.c (do_test): Add a const. 2005-12-27 22:50:12 +00:00
inet_addr.c Change inet_aton type from in_addr_t to int. 2004-07-21 16:28:40 +00:00
inet_net_ntop.c Update. 2004-09-14 04:41:35 +00:00
inet_net_pton.c Update. 2004-09-14 04:41:35 +00:00
inet_neta.c Update. 2000-07-19 22:03:58 +00:00
inet_ntop.c * nscd/selinux.c (preserve_capabilities): Initialize new_caps 2007-07-28 20:44:03 +00:00
inet_pton.c [BZ #295] 2004-08-05 16:27:58 +00:00
Makefile Consistently include Makeconfig after defining subdir. 2014-02-26 23:12:03 +00:00
mapv4v6addr.h . 2007-07-31 13:33:18 +00:00
mapv4v6hostent.h Handle running out of buffer space with IPv6 mapping enabled. 2009-11-10 07:36:50 -08:00
netdb.h Complete _BSD_SOURCE / _SVID_source followup cleanup. 2014-02-21 21:45:26 +00:00
ns_date.c * Versions.def: Add GLIBC_2.9 to libresolv. 2008-08-01 17:16:31 +00:00
ns_name.c Fix typos. 2013-08-30 18:08:59 +02:00
ns_netint.c * Versions.def: Add GLIBC_2.9 to libresolv. 2008-08-01 17:16:31 +00:00
ns_parse.c * Versions.def: Add GLIBC_2.9 to libresolv. 2008-08-01 17:16:31 +00:00
ns_print.c Avoid use of "register" as optimization hint. 2013-06-07 22:24:35 +00:00
ns_samedomain.c Fix typos. 2013-08-21 19:48:48 +02:00
ns_ttl.c * Versions.def: Add GLIBC_2.9 to libresolv. 2008-08-01 17:16:31 +00:00
nsap_addr.c * include/libc-symbols.h (__libc_freeres_fn_section, libc_freeres_fn): 2002-11-01 20:44:15 +00:00
README Remove trailing whitespace. 2013-06-05 20:44:03 +00:00
res_comp.c Fix typos. 2013-08-29 09:11:45 +02:00
res_data.c Fix leading whitespaces. 2013-06-06 20:36:07 +02:00
res_debug.c BZ#15084: Apparent typos in strings in res_debug.c 2013-04-29 21:17:30 +02:00
res_debug.h Remove trailing whitespace. 2013-06-05 20:44:03 +00:00
res_hconf.c Update copyright notices with scripts/update-copyrights 2014-01-01 22:00:23 +10:00
res_hconf.h Update copyright notices with scripts/update-copyrights 2014-01-01 22:00:23 +10:00
res_init.c Use glibc_likely instead __builtin_expect. 2014-02-10 15:07:12 +01:00
res_libc.c Remove --disable-versioning. 2013-09-04 15:25:42 +00:00
res_mkquery.c Use glibc_likely instead __builtin_expect. 2014-02-10 15:07:12 +01:00
res_query.c Properly fix memory leak in _nss_dns_gethostbyname4_r with big DNS answer 2014-02-19 14:39:21 +01:00
res_send.c Properly fix memory leak in _nss_dns_gethostbyname4_r with big DNS answer 2014-02-19 14:39:21 +01:00
res-state.c Update copyright notices with scripts/update-copyrights 2014-01-01 22:00:23 +10:00
resolv.h BZ#15085: Fix comments/strings for RES_NOCHECKNAME 2013-04-29 21:11:13 +02:00
tst-aton.c Add #include <stdint.h> for uint[32|64]_t usage (except installed headers). 2013-05-16 11:32:54 -05:00
tst-inet_ntop.c Remove trailing whitespace. 2013-06-05 20:44:03 +00:00
tst-leaks2.c Update copyright notices with scripts/update-copyrights 2014-01-01 22:00:23 +10:00
tst-leaks.c Update copyright notices with scripts/update-copyrights 2014-01-01 22:00:23 +10:00
Versions Remove unused %include lines from Versions files. 2014-02-22 00:58:54 -08:00

The resolver in the GNU C Library
*********************************

Starting with version 2.2, the resolver in the GNU C Library comes
from BIND 8.  Only a subset of the src/lib/resolv part of libbind is
included here; basically the parts that are needed to provide the
functionality present in the resolver from BIND 4.9.7 that was
included in the previous release of the GNU C Library, augmented by
the parts needed to provide thread-safety.  This means that support
for things as dynamic DNS updates and TSIG keys isn't included.  If
you need those facilities, please take a look at the full BIND
distribution.


Differences
===========

The resolver in the GNU C Library still differs from what's in BIND
8.2.3-T5B:

* The resolver in glibc strictly adheres to the recommendations in RFC
  1535.  BIND 8.2.3-T5B seems to relax those rules a bit (see the code
  that's wrapped in `#ifndef RFC1535').

* The RES_DEBUG option (`options debug' in /etc/resolv.conf) has been
  disabled.

* The resolver in glibc allows underscores in domain names.

* The <resolv.h> header in glibc includes <netinet/in.h> and
  <arpa/nameser.h> to make it self-contained.

* The `res_close' function in glibc only tries to close open files
  referenced through `_res' if the RES_INIT bit is set in
  `_res.options'.  This fixes a potential security bug with programs
  that bogusly call `res_close' without initialising the resolver
  state first.  Note that the thread-safe `res_nclose' still doesn't
  check the RES_INIT bit.  By the way, you're not really supposed to
  call `res_close/res_nclose' directly.

* The resolver in glibc can connect to a nameserver over IPv6.  Just
  specify the IPv6 address in /etc/resolv.conf.  You cannot change the
  address of an IPv6 nameserver dynamically in your program though.


Using the resolver in multi-threaded code
=========================================

The traditional resolver interfaces `res_query', `res_search',
`res_mkquery', `res_send' and `res_init', used a static (global)
resolver state stored in the `_res' structure.  Therefore, these
interfaces are not thread-safe.  Therefore, BIND 8.2 introduced a set
of "new" interfaces `res_nquery', `res_nsearch', `res_nmkquery',
`res_nsend' and `res_ninit' that take a `res_state' as their first
argument, so you can use a per-thread resolver state.  In glibc, when
you link with -lpthread, such a per-thread resolver state is already
present.  It can be accessed using `_res', which has been redefined as
a macro, in a similar way to what has been done for the `errno' and
`h_errno' variables.  This per-thread resolver state is also used for
the `gethostby*' family of functions, which means that for example
`gethostbyname_r' is now fully thread-safe and re-entrant.  The
traditional resolver interfaces however, continue to use a single
resolver state and are therefore still thread-unsafe.  The resolver
state is the same resolver state that is used for the initial ("main")
thread.

This has the following consequences for existing binaries and source
code:

* Single-threaded programs will continue to work.  There should be no
  user-visible changes when you recompile them.

* Multi-threaded programs that use the traditional resolver interfaces
  in the "main" thread should continue to work, except that they no
  longer see any changes in the global resolver state caused by calls
  to, for example, `gethostbyname' in other threads.  Again there
  should be no user-visible changes when you recompile these programs.

* Multi-threaded programs that use the traditional resolver interfaces
  in more than one thread should be just as buggy as before (there are
  no problems if you use proper locking of course).  If you recompile
  these programs, manipulating the _res structure in threads other
  than the "main" thread will seem to have no effect though.

* In Multi-threaded that manipulate the _res structure, calls to
  functions like `gethostbyname' in threads other than the "main"
  thread won't be influenced by the those changes anymore.  So if you
  set RES_USE_INET6, a call to `gethostbyname' won't return any IPv6
  hosts anymore.  If you recompile such programs, manipulating the
  _res structure will affect the thread in which you do so instead of
  the "main" thread.

We recommend to use the new thread-safe interfaces in new code, since
the traditional interfaces have been deprecated by the BIND folks.
For compatibility with other (older) systems you might want to
continue to use those interfaces though.


Using the resolver in C++ code
==============================

There resolver contains some hooks which will allow the user to
install some callback functions that make it possible to filter DNS
requests and responses.  Although we do not encourage you to make use
of this facility at all, C++ developers should realise that it isn't
safe to throw exceptions from such callback functions.


Source code
===========

The following files come from the BIND distribution (currently version
8.2.3-T5B):

src/include/
  arpa/nameser.h
  arpa/nameser_compat.h
  resolv.h

src/lib/resolv/
  herror.c
  res_comp.c
  res_data.c
  res_debug.c
  res_debug.h
  res_init.c
  res_mkquery.c
  res_query.c
  res_send.c

src/lib/nameser/
  ns_name.c
  ns_netint.c
  ns_parse.c
  ns_print.c
  ns_samedomain.c
  ns_ttl.c

src/lib/inet/
  inet_addr.c
  inet_net_ntop.c
  inet_net_pton.c
  inet_neta.c
  inet_ntop.c
  inet_pton.c
  nsap_addr.c

src/lib/isc/
  base64.c

Some of these files have been optimised a bit, and adaptations have
been made to make them fit in with the rest of glibc.  The more
non-obvious changes are wrapped in something like `#ifdef _LIBC'.

res_libc.c is home-brewn, although parts of it are taken from res_data.c.

res_hconf.c and res_hconf.h were contributed by David Mosberger, and
do not come from BIND.

The files gethnamaddr.c, mapv4v6addr.h and mapv4v6hostent.h are
leftovers from BIND 4.9.7.