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Re: ac-archive: ac_sys_largefile and libraries...


From: Paul Eggert
Subject: Re: ac-archive: ac_sys_largefile and libraries...
Date: Sat, 11 Jan 2003 10:07:37 -0800 (PST)

> Date: Sat, 11 Jan 2003 18:45:30 +0100
> From: Guido Draheim <address@hidden>
> 
> See the note about zlib - it might screw you up.

We cannot eliminate the possibility of screwups.  We can only make
them less likely, in the normal cases by ordinary developers.

The simplest way to do this is to make 64-bit off_t the default, and
to make people have to go out of their way to use 32-bit off_t.

> The problem only exists when off_t creeps into public headers usable
> by third party applications,

Not true.  The problem can exist even if the public headers export
only 'int'.  For example, libraries can export large-file-aware file
descriptors into non-large-file-aware applications.  And it can also
exist even if the public headers export only 'long'; ftell is an
example of this problem.

The problem of supporting mixed-mode applications is much more
complicated than what you seem to be suggesting.  We should not
suggest to developers that they take that path.  It is a long, hard,
and bug-prone road, and there's little payoff at the end.

We should instead tell people the much simpler solution: don't mix
object modules compiled in different modes.  This is easy to
understand, and it works.

> +checking for off_t... yes (largefile sensitive)
> 
> A developer will surely see it and try to get the answer as to
> what that actually means

I'm skeptical.  Most people don't read or understand those messages,
unless perhaps the compilation fails.

How about if we change AC_TYPE_OFF_T to invoke AC_SYS_LARGEFILE by
default?  If you want a small-file program, you'd have to invoke
AC_CHECK_TYPE(off_t, long) instead.  That might help a bit.

But I'm becoming more inclined to think that we should invoke
AC_SYS_LARGEFILE by default, unless the user explicitly says he wants
32-bit off_t.




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