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Date: Wed, 12 Feb 2014 11:16:17 -0500
From: Ken Brown <kbrown AT cornell DOT edu>
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To: cygwin AT cygwin DOT com
Subject: Re: get rid of getpwent? (Was: cygwin-1.7.28 getpwent header declaration changes ?)
References: <31347914-BB4F-4039-984B-731B6C72F903 AT etr-usa DOT com> <52F7AEC5 DOT 5090205 AT tiscali DOT co DOT uk> <8B7B5FE0-7413-4358-BA8A-E0B6E0B17653 AT etr-usa DOT com> <52F8B50E DOT 7040307 AT lysator DOT liu DOT se> <52F92D58 DOT 9030408 AT etr-usa DOT com> <52F95D1D DOT 4050108 AT tiscali DOT co DOT uk> <4510121021 DOT 20140211062515 AT mtu-net DOT ru> <52FAB14C DOT 8060800 AT tiscali DOT co DOT uk> <52FABAF5 DOT 2060701 AT etr-usa DOT com> <52FAD730 DOT 9090507 AT redhat DOT com> <20140212090804 DOT GM2821 AT calimero DOT vinschen DOT de>
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On 2/12/2014 4:08 AM, Corinna Vinschen wrote:
> On Feb 11 19:06, Eric Blake wrote:
>> On 02/11/2014 05:06 PM, Warren Young wrote:
>>> On 2/11/2014 16:25, David Stacey wrote:
>>>> getpwent() is called in three different places.
>>>
>>> To those of you who have investigated these code paths: do any of them
>>> look like they couldn't be replaced by getpwnam() or other calls that
>>> would let cygwin1.dll do single-record AD/SAM lookups, rather than
>>> whole-table/tree scans?
>>>
>>> That is, do any of these programs really need to visit every record in
>>> /etc/passwd?
>>
>> libreadline wants to know how to tab-complete ~foo; to do that, it has
>> to find all usernames beginning with foo.  How would you do that without
>> visiting every single record?
>
> This seems to be the major usage of getpwent these days.  The question
> is, how bad is it if only a handful entries, or even only a single one
> (of oneself) show up?
>
> Either way, implementing a full getpwent requires to return the local
> users, the users of the primary domain, and the users of all trusted
> domains.  I know of domains with 200K users and there are probably
> bigger ones.  How long should a search take when a user presses <TAB>
> after the ~?  And then, shall the process running the getpwent actually
> cache all of them?  This seems really excessive.

What about the following compromise:  If /etc/passwd exists, then 
getpwent behaves as it does currently.  Otherwise, it returns a handful 
of entries, or possibly just the current user.  This gives users a 
choice.  If tab-completion in this situation is important to them, they 
can keep their /etc/passwd file.

Ken

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