Date: Mon, 29 Jan 2001 15:00:23 -0500 (EST) From: Garrett Wollman <wollman@khavrinen.lcs.mit.edu> To: Luigi Rizzo <rizzo@aciri.org> Cc: hackers@FreeBSD.ORG Subject: Re: [kernel patch] fcntl(...) to close many descriptors Message-ID: <200101292000.PAA37796@khavrinen.lcs.mit.edu> In-Reply-To: <200101291926.f0TJQYK34514@iguana.aciri.org> References: <20010129112337.Y26076@fw.wintelcom.net> <200101291926.f0TJQYK34514@iguana.aciri.org>
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<<On Mon, 29 Jan 2001 11:26:29 -0800 (PST), Luigi Rizzo <rizzo@aciri.org> said:
> but there is a problem with syscall() in that according to
> the manpages it cannot handle in/out parameters as instead
> it is supported by ioctl/fcntl
Of course it can, and the manual page doesn't even suggest what you
say. It says:
There is no way to simulate system calls that have multiple return values
such as pipe(2).
pipe(2) is a special case in that it returns two values rather than
one. The actual pipe(2) system call has *no* formal parameters; the
unpacking of the two values returned into the declared C formal
parameter is done by an assembly-language stub. (This was done for
reasons of speed; it is much faster to return two values than it is to
copyout() a two-element array.
If you were implementing a Lisp binding of POSIX, you would probably
define PIPE to be a niladic function which returns a list of two
descriptors.
-GAWollman
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