resolver ... again

Klacke <>
Fri Jun 6 13:09:35 CEST 2003


Howdy,

The code in inet_config.erl is not quite right.
On linux, the code in the inet_config:init/0
reads /etc/hosts.conf (only)

The glibc resolver reads both the /etc/host.conf aswell
as /etc/nsswitch.conf

A very old system

[ /root]# cat /etc/redhat-release 
Red Hat Linux release 6.2 (Zoot)
[ /root]#  strace ping -c 1 www.erlang.org 2>&1 | grep '/etc/.*.conf'
open("/etc/resolv.conf", O_RDONLY)      = 4
open("/etc/nsswitch.conf", O_RDONLY)    = 4
read(4, "#\n# /etc/nsswitch.conf\n#\n# An ex"..., 4096) = 1767
open("/etc/host.conf", O_RDONLY)        = 4


Slightly newer ....

# cat /etc/redhat-release
Red Hat Linux release 7.3 (Valhalla)
# strace ping -c 1 www.erlang.org 2>&1 | grep '/etc/.*.conf'
open("/etc/resolv.conf", O_RDONLY)      = 3
open("/etc/nsswitch.conf", O_RDONLY)    = 3
read(3, "#\n# /etc/nsswitch.conf\n#\n# An ex"..., 4096) = 1682
open("/etc/host.conf", O_RDONLY)        = 3


And then to the boring part:

tita root # uname -a
Linux tita 2.4.20-gentoo-r5-1 #1 SMP Wed Jun 4 16:51:01 CEST 2003 i686 Intel(R) Pentium(R) 4 CPU 2.20GHz GenuineIntel GNU/Linux
tita root # strace ping -c 1 www.erlang.org 2>&1 | grep '/etc/.*.conf'
open("/etc/nsswitch.conf", O_RDONLY)    = 3
read(3, "# /etc/nsswitch.conf:\n# $Header:"..., 4096) = 498
open("/etc/resolv.conf", O_RDONLY)      = 4
open("/etc/host.conf", O_RDONLY)        = -1 ENOENT (No such file or directory)



Gentoo doesn't have the /etc/host.conf file.
This does indeed make sence, having two _different_ files
controling the behaviour of the resolver is broken.

The erlang code _only_ reads the /etc/host.conf file, in order to

a) work on gentoo
b) be more glibc like

We should at least also read the /etc/nsswitch.conf file.
Preferable we should first read /etc/nsswitch.conf and then
if that fails read /etc/host.conf

The /etc/hosts.conf file is an old BSDism and I think that
very few tools (except OTP then :-) works with that file.


Here's a possible patch, reading /etc/hosts.conf first and then
/etc/nsswitch.conf
But as I wrote, even better would be to read nsswitch before hosts.
People are probably more accustomed to changing the nsswitch 
file than the host file.


Enjoy.



/klacke



-- 
Claes Wikstrom                        -- Caps lock is nowhere and
Alteon WebSystems                     -- everything is under control          
http://www.bluetail.com/~klacke      
cellphone: +46 70 2097763
-------------- next part --------------
Index: inet_config.erl
===================================================================
RCS file: /home/share/erlang/cvsroot/otp/lib/kernel/src/inet_config.erl,v
retrieving revision 1.5
diff -c -b -r1.5 inet_config.erl
*** inet_config.erl	25 Feb 2003 13:37:22 -0000	1.5
--- inet_config.erl	6 Jun 2003 11:00:35 -0000
***************
*** 82,88 ****
  		'bsd/os' ->
  		    load_resolv(filename:join(Etc,"irs.conf"), host_conf_bsdos);
  		linux ->
! 		    load_resolv(filename:join(Etc,"host.conf"),host_conf_linux),
  
  		    % It may be the case that the domain name was not set
  		    % because the hostname was short. But we can now look it
--- 82,93 ----
  		'bsd/os' ->
  		    load_resolv(filename:join(Etc,"irs.conf"), host_conf_bsdos);
  		linux ->
! 		    case load_resolv(filename:join(Etc,"host.conf"),host_conf_linux) of
! 			ok ->
! 			    ok;
! 			_Other ->
! 			    load_resolv(filename:join(Etc,"nsswitch.conf"), nsswitch_conf)
! 		    end,
  		    
  		    % It may be the case that the domain name was not set
  		    % because the hostname was short. But we can now look it
***************
*** 296,305 ****
  	    case apply(inet_parse, Func, [File,{chars,Bin}]) of
  		{ok, Ls} -> inet_db:add_rc_list(Ls);
  		{error, Reason} ->
! 		    error("parse error in file ~s: ~p", [File, Reason])
  	    end;
  	Error ->
! 	    warning("file not found ~s~n", [File])
      end.
  
  %%
--- 301,312 ----
  	    case apply(inet_parse, Func, [File,{chars,Bin}]) of
  		{ok, Ls} -> inet_db:add_rc_list(Ls);
  		{error, Reason} ->
! 		    error("parse error in file ~s: ~p", [File, Reason]),
! 		    {error, Reason}
  	    end;
  	Error ->
! 	    warning("file not found ~s~n", [File]),
! 	    Error
      end.
  
  %%


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