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Date: Fri, 15 Mar 2013 14:43:00 -0400
From: Rich Felker <dalias@...ifal.cx>
To: musl@...ts.openwall.com
Subject: Re: question: hard-coded file descriptors in
stdin/stdout/stderr
On Fri, Mar 15, 2013 at 10:46:54AM -0400, Zvi Gilboa wrote:
> >> [Rich wrote:] Not only are the numbers 0/1/2 specified and widely
> hard-coded in applications;
>
> >> [LM wrote:] I've been trying to port msh to Windows and it uses
> hard-coded 0, 1 and 2 with pipes and expects them to mean stdin,
> stdout and stderr.
>
> Thank you for this valuable input! Clearly, remapping 0/1/2 from
> within psxcalls would be the only responsible approach:)
Note that even if the shell doesn't hard-code them, every single
non-trivial shell script ever written hard-codes them. I think this
was the motivation for POSIX requiring that they have the specific
values 0/1/2.
> That kind of "translation" is an essential part of the psxcalls
> project. Surprisingly (or not), the vast majority of differences
> between the Native API and POSIX are about syntax, not
> functionality. In other words, there exist only very few POSIX
> features that cannot be implemented using the Native API in a
> straight-forward way. There are for sure some cases that require
That's nice to hear. I suspect there are a lot more subtleties like
different error conditions and corner cases, which probably need
consideration on a case-by-case basis whether it's important to match
the POSIX behavior (or whether it's even possible to match it
exactly). Still, I think most such problems are things that can be
solved incrementally, and shouldn't stall the project.
> programming acrobatics (fork() and exec()) being the most obvious
> examples), but that's the exception, not the rule. Whenever I
> implement one of the functions, I try to phrase the task in the form
> of a question, for instance: "using the Native API, how would you
> map a memory page to the address space of a user applications?"
> That kind of approach to writing the library surely entails a lot of
> work, but is also very exciting -- like solving a puzzle every
> single day...
Keep up the good spirits -- I'm glad to see this finally happening. My
hope for the past 7+ years has been that we could get to a point where
software (or at least FOSS) could be written with a portable core
targetting POSIX rather than having windows-specific hacks all over
the core to deal with the badness of msvcrt, or bloated "portable
runtime" libraries that layer abstractions on top of the standardized
abstractions.
Rich
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