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Date: Wed, 12 Feb 2014 08:35:40 -0800 (PST)
From: Richard <richard@KarmannGhia.org>
To: Ken Brown <kbrown@cornell.edu>
cc: cygwin@cygwin.com
Subject: Re: get rid of getpwent? (Was: cygwin-1.7.28 getpwent header declaration changes ?)
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On Wed, 12 Feb 2014, Ken Brown wrote:
> 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.

Works for me! And I'd vote "just the current user" in lieu of "a handful" 
because even a handful has a huge overhead associated with it.

Richard

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