Re: make-network-process's gethostbyname usage

["Jan Djärv" <jan.h.d@swipnet.se>]

Chong Yidong skrev:
> storm@cua.dk (Kim F. Storm) writes:
> 
>> Richard Stallman <rms@gnu.org> writes:
>>
>>>     make-network-process calles gethostbyname, but never calls
>>>     res_init. The problem, which appears is: if contents of
>>>     /etc/resolv.conf was changed old dns servers are unavailable,
>>>     gethostbyname still tries them, not new ones. So this bug is pretty
>>>     much the same as http://bugs.debian.org/438680 (which has a patch).
>>>
>>> Would someone please DTRT about this, then ack?
>>> It needs to be fixed in Emacs 22.
>> I don't know what to do about this.
>>
>> configure already has a check for res_init, but on my system (GNU/Linux),
>> HAVE_RES_INIT is undefined, indicating that it doesn't exist.
>>
>> However, I believe that it does exist, but only if -lresolv is specified.
>>
>> So how can we fix configure to DTRT?
> 
> See the attached patch.
> 
> Strangely enough, even though autoconf needs -lresolv to detect
> res_init(), it doesn't seem as though we need to add -lresolv when
> compiling Emacs itself.  I don't know why this should be the case.
> Does anyone have an idea?

Probably some magic in GNU libc, I would not rely on this working on other
systems that don't use GNU libc and/or linker.

You should use the predefined macros instead of using AC_TRY_LINK, in this
case AC_CHECK_LIB.

	Jan D.

> 
> *** emacs/configure.in.~1.444.2.2.~	2007-08-22 17:50:31.000000000 -0400
> --- emacs/configure.in	2007-08-25 14:34:43.000000000 -0400
> ***************
> *** 2580,2586 ****
>   
>   AC_CHECK_FUNCS(gethostname getdomainname dup2 \
>   rename closedir mkdir rmdir sysinfo getrusage get_current_dir_name \
> ! random lrand48 bcopy bcmp logb frexp fmod rint cbrt ftime res_init setsid \
>   strerror fpathconf select mktime euidaccess getpagesize tzset setlocale \
>   utimes setrlimit setpgid getcwd getwd shutdown getaddrinfo \
>   __fpending mblen mbrlen mbsinit strsignal setitimer ualarm index rindex \
> --- 2580,2586 ----
>   
>   AC_CHECK_FUNCS(gethostname getdomainname dup2 \
>   rename closedir mkdir rmdir sysinfo getrusage get_current_dir_name \
> ! random lrand48 bcopy bcmp logb frexp fmod rint cbrt ftime setsid \
>   strerror fpathconf select mktime euidaccess getpagesize tzset setlocale \
>   utimes setrlimit setpgid getcwd getwd shutdown getaddrinfo \
>   __fpending mblen mbrlen mbsinit strsignal setitimer ualarm index rindex \
> ***************
> *** 2624,2640 ****
>   # than to expect to find it in ncurses.
>   AC_CHECK_LIB(ncurses, tparm)
>   
>   # Do we need the Hesiod library to provide the support routines?
>   if test "$with_hesiod" = yes ; then
>     # Don't set $LIBS here -- see comments above.
> -   resolv=no
>     AC_CHECK_FUNC(res_send, , [AC_CHECK_FUNC(__res_send, ,
>        [AC_CHECK_LIB(resolv, res_send, resolv=yes,
>   		  [AC_CHECK_LIB(resolv, __res_send, resolv=yes)])])])
>     if test "$resolv" = yes ; then
>       RESOLVLIB=-lresolv
> -     AC_DEFINE(HAVE_LIBRESOLV, 1,
> - 	      [Define to 1 if you have the resolv library (-lresolv).])
>     else
>       RESOLVLIB=
>     fi
> --- 2624,2662 ----
>   # than to expect to find it in ncurses.
>   AC_CHECK_LIB(ncurses, tparm)
>   
> + resolv=no
> + 
> + # Do we have res_init, for detecting changes in /etc/resolv.conf?
> + 
> + AC_CHECK_FUNC(res_init, have_res_init=yes, have_res_init=no)
> + if test "$have_res_init" = no; then
> +   OLIBS="$LIBS"
> +   LIBS="$LIBS -lresolv"
> +   AC_MSG_CHECKING(for res_init with -lresolv)
> +   AC_TRY_LINK([#include <netinet/in.h>
> + #include <arpa/nameser.h>
> + #include <resolv.h> ],
> +     [res_init();],
> +     have_res_init=yes, have_res_init=no)
> +   AC_MSG_RESULT($have_res_init)
> +   if test "$have_res_init" = yes ; then
> +     resolv=yes
> +   fi
> +   LIBS="$OLIBS"
> + fi
> + 
> + if test "$have_res_init" = yes; then
> +   AC_DEFINE(HAVE_RES_INIT, 1, [Define to 1 if res_init is available.])
> + fi
> + 
>   # Do we need the Hesiod library to provide the support routines?
>   if test "$with_hesiod" = yes ; then
>     # Don't set $LIBS here -- see comments above.
>     AC_CHECK_FUNC(res_send, , [AC_CHECK_FUNC(__res_send, ,
>        [AC_CHECK_LIB(resolv, res_send, resolv=yes,
>   		  [AC_CHECK_LIB(resolv, __res_send, resolv=yes)])])])
>     if test "$resolv" = yes ; then
>       RESOLVLIB=-lresolv
>     else
>       RESOLVLIB=
>     fi
> ***************
> *** 2644,2649 ****
> --- 2666,2677 ----
>   	:, $RESOLVLIB)])
>   fi
>   
> + # Do we need libresolv (due to res_init or Hesiod)?
> + if test "$resolv" = yes ; then
> +   AC_DEFINE(HAVE_LIBRESOLV, 1,
> +             [Define to 1 if you have the resolv library (-lresolv).])
> + fi
> + 
>   # These tell us which Kerberos-related libraries to use.
>   if test "${with_kerberos+set}" = set; then
>     AC_CHECK_LIB(com_err, com_err)
> *** emacs/src/process.c.~1.512.2.4.~	2007-08-08 14:07:26.000000000 -0400
> --- emacs/src/process.c	2007-08-25 14:56:59.000000000 -0400
> ***************
> *** 129,134 ****
> --- 129,140 ----
>   # endif
>   #endif
>   
> + #ifdef HAVE_RES_INIT
> + #include <netinet/in.h>
> + #include <arpa/nameser.h>
> + #include <resolv.h>
> + #endif
> + 
>   #include "lisp.h"
>   #include "systime.h"
>   #include "systty.h"
> ***************
> *** 3082,3087 ****
> --- 3088,3098 ----
>         hints.ai_family = family;
>         hints.ai_socktype = socktype;
>         hints.ai_protocol = 0;
> + 
> + #ifdef HAVE_RES_INIT
> +       res_init ();
> + #endif
> + 
>         ret = getaddrinfo (SDATA (host), portstring, &hints, &res);
>         if (ret)
>   #ifdef HAVE_GAI_STRERROR
> ***************
> *** 3127,3132 ****
> --- 3138,3148 ----
>   	 as it may `hang' Emacs for a very long time.  */
>         immediate_quit = 1;
>         QUIT;
> + 
> + #ifdef HAVE_RES_INIT
> +       res_init ();
> + #endif
> + 
>         host_info_ptr = gethostbyname (SDATA (host));
>         immediate_quit = 0;
>   
> 
> 
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