Re: [patch] gethostbyname.3: NSS plugins searched first.

["Carlos O'Donell" <carlos-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On 04/30/2015 04:49 AM, Michael Kerrisk (man-pages) wrote:
> [CC += Stéphane, since he's been working on related pages recently]
> 
> Hi Carlos,
> 
> On 04/29/2015 07:24 PM, Carlos O'Donell wrote:
>> The gethostbyname man page should first and foremost list that
>> the source of the data comes from the NSS plugins. I accept
>> that the man page is intentionally trying to be vague because
>> these things are not guaranteed anywhere, the truth is far
>> more mundane and "default" here IMO applies to a normal glibc
>> installation on Linux, and the fallback is always a localhost
>> nameserver.
>>
>> I suggest the following changes, but feel free to reword as
>> you see fit.
> 
> Thanks. Applied, with a few formatting teaks.
> 
> One question below.
> 
>> Patch against master.
>>
>> Signed-off-by: Carlos O'Donell <carlos-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
>>
>> diff --git a/man3/gethostbyname.3 b/man3/gethostbyname.3
>> index 7875f88..59c7bb1 100644
>> --- a/man3/gethostbyname.3
>> +++ b/man3/gethostbyname.3
>> @@ -224,18 +224,20 @@ The domain name queries carried out by
>>  .BR gethostbyname ()
>>  and
>>  .BR gethostbyaddr ()
>> -use a combination of any or all of the name server
>> +use a combination of any or all of Name Service Switch
>> +.BR nsswitch.conf(5)
>> +configured sources, name servers in \fI/etc/resolv.conf\fP
>> +.BR resolv.conf(5),
>> +a local name server
>>  .BR named (8),
>>  a broken out line from \fI/etc/hosts\fP, and the Network
>>  Information Service (NIS or YP), depending upon the contents of the
>>  \fIorder\fP line in
>>  .IR /etc/host.conf .
> 
> Your patch didn't change the last few lines, but you may be able to
> help... Is the reference to "order" and /etc/host.conf on this page not
> obsolete by now. Looking at host.conf(5), one sees, 

No, order *is* obsolete.

>   Historical
>        The  nsswitch.conf(5) file is the modern way of controlling the
>        order of host lookups.
> 
>        In glibc 2.4 and earlier, the following keyword is recognized:
> 
>        order  This keyword specifies how host lookups are to  be  per‐
>               formed.   It  should  be  followed by one or more lookup
>               methods, separated by commas.  Valid methods  are  bind,
>               hosts, and nis.
> 
> So, it looks like some fix is required here also. Right?

Yes. I didn't know how we wanted to talk about this particular topic.
The use of "order" is obsolete as of 2.5.

The following is a sketch of how I'd rewrite this to be more correct,
I'm out of time for today, but if you want to fix the formatting and
check it in that would be awesome.

diff --git a/man3/gethostbyname.3 b/man3/gethostbyname.3
index 96f8cd6..5ce1e17 100644
--- a/man3/gethostbyname.3
+++ b/man3/gethostbyname.3
@@ -224,23 +224,26 @@ The domain name queries carried out by
 .BR gethostbyname ()
 and
 .BR gethostbyaddr ()
-use a combination of any or all of the Name Service Switch
+rely on the Name Service Switch
 .RB ( nsswitch.conf (5))
-configured sources, name servers in \fI/etc/resolv.conf\fP
-.RB ( resolv.conf (5)),
-a local name server
-.RB ( named (8)),
-a broken-out line from
-.IR /etc/hosts
-.RB ( hosts (5)),
-and the Network
-Information Service (NIS or YP), depending on the contents of the
-\fIorder\fP line in
-.IR /etc/host.conf .
+configured sources or a local name server
+.RB ( named (8)).
 The default action is to query the Name Service Switch
 .RB ( nsswitch.conf(5))
-configured sources, followed by a local name server
+configured sources, failing that, a local name server
 .RB ( named (8)).
+
+.SS Historical
+The
+.BR nsswitch.conf (5)
+file is the modern way of controlling the order of host lookups.
+.PP
+In glibc 2.4 and earlier, the
+.I order
+keyword was used to control the order of host lookups as defined in
+.IR /etc/host.conf
+.RB ( host.conf(5)).
+
 .PP
 The \fIhostent\fP structure is defined in \fI<netdb.h>\fP as follows:
 .sp
---

Cheers,
Carlos.




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