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Date: Mon, 18 Dec 2006 10:43:12 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: wtmpx support
Message-ID: <20061218094312.GC8345@calimero.vinschen.de>
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On Dec 17 22:31, Charles Wilson wrote:
> I think that winsup/cygwin/include/utmpx.h should include the following 
> definition, similar to the existing one for UTMPX_FILE:
> 
> #define WTMPX_FILE _PATH_WTMP
> 
> I'm hitting a compile error in rxvt-unicode:
> 
> # if defined(HAVE_STRUCT_UTMPX) && defined(HAVE_UPDWTMPX)
>       updwtmpx (WTMPX_FILE, utx);
> # endif
> 
> 
> Both HAVE_STRUCT_UTMPX and HAVE_UPDWTMPX are true, so I think we ought 
> also to have WTMPX_FILE.  Since cygwin's utmp/wtmp file formats seem to 
> be arranged so that they can be opened and used without error by 
> functions that expect to populate either struct utmp OR struct utmpx, we 
> can use _PATH_UTMP for UTMP_FILE and UTMPX_FILE interchangeably -- that 
> part is already in cygwin's code.  The same logic, I think, holds for 
> _PATH_WTMP, WTMP_FILE, and WTMPX_FILE.
> 
> Hence the requested #define, above.

I was going to do that at one point but I had a reason not to.

When I created the utmpx/wtmpx handling, I intended to keep backward
compatible with the existing utmp and wtmp files.  So the utmpx/wtmpx
functions are only wrappers around the utmp/wtmp functions and the
file format is that of utmp/wtmp.

Unfortunately there are applications which access the wtmp file
manually, namely tools to inspect the content, for instance, last(1).

If the WTMPX_FILE define is present, last tries to read this file in
wtmpx format and fails.

A couple of weeks ago I started to switch Cygwin to the wtmpx format
but the problem is the same, just backwards.  The only way I see to
keep backwards compatibility while switching to a new format is to
use new files /var/log/utmpx and /var/run/wtmpx.  In theory, this
should only require to rebuild the inspection tools like last.  But
it wouldn't be a nice transition, rather a cut.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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