Date: Tue, 25 Jan 2005 14:15:45 +0300 From: Andrey Chernov <ache@nagual.pp.ru> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: cvs-all@FreeBSD.ORG Subject: Re: cvs commit: src/sys/kern sys_generic.c Message-ID: <20050125111545.GC29791@nagual.pp.ru> In-Reply-To: <81495.1106650943@critter.freebsd.dk> References: <20050125105811.GA29791@nagual.pp.ru> <81495.1106650943@critter.freebsd.dk>
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On Tue, Jan 25, 2005 at 12:02:23PM +0100, Poul-Henning Kamp wrote: > >> >"This volume of IEEE Std 1003.1-2001 requires that no action be taken for > >> >read() or write() when nbyte is zero. This is not intended to take > >> >precedence over detection of errors (such as invalid buffer pointers or > >> >file descriptors). This is consistent with the rest of this volume of IEEE > >> >Std 1003.1-2001, but the phrasing here could be misread to require > >> >detection of the zero case before any other errors." > > Std 1003.1-2001, but the phrasing here could be misread to require > detection of the zero case before any other errors." > > Does not say you are not allowed to check for the zero case first, only that > you are not required to do so. The quote above is not complete, last phrase slips in the exchange: "A value of zero is to be considered a correct value, for which the semantics are a no-op." For any correct value read() checks some FS-dependent errors conditions and may return errors, but not for zero value now. It means we can't now call zero value "correct". "No-op" does not means error conditions should be skipped. Instead, it means that non-error case operation is empty. -- http://ache.pp.ru/
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