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Date: Sat, 23 Mar 2013 22:27:14 -0400
From: Zvi Gilboa <zg7s@...rvices.virginia.edu>
To: <musl@...ts.openwall.com>
Subject: Re: Difficulty emulating F_DUPFD_CLOEXEC
On 03/23/2013 10:17 PM, Rich Felker wrote:
> On Sat, Mar 23, 2013 at 10:10:10PM -0400, Zvi Gilboa wrote:
>>> This uglifies fcntl.c a bit more, but I think it works. Does the above
>>> reasoning make sense? Any other ideas?
>> In the hope that this matches the project's spirit... how about
>> running these tests during the build, and have a script (or a simple
>> test program) #define whether the target architecture supports
>> F_DUPFD_CLOEXEC or not? Potentially, this test could be added at
>> the very end of alltypes.h.sh
> It's not a matter of the architecture. It's a matter of the kernel
> version. F_DUPFD_CLOEXEC was not available until late in the 2.6
> series, and musl aims to "mostly work" even with early 2.6, and to
> "partly work" (at least for single-threaded programs that don't use
> modern features) even on 2.4. For dynamic linking, it could make sense
> to have a slimmer version of libc.so that only supports up-to-date
> kernels, but for static linking, it's really frustrating to have
> binaries that break on older kernels, even if it is the broken
> kernel's fault.
>
> If the lack of these features were just breaking _apps_ that use them,
> it would be one thing, but several of the very-new atomic
> close-on-exec interfaces needed internally in musl for some core
> functionality -- things like dns lookups, popen, system, etc. Thus
> failure to emulate them when the kernel doesn't have working versions
> could badly break even "simple" apps that would otherwise be expected
> to work even on old kernels.
... thanks, that makes perfect sense. As a second-best try: would it
makes sense to run the long feature test just once, during startup (and
save its result to some global variable), instead of inside fcntl.c?
>
> Rich
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