Date: 03 Jun 2003 22:04:56 +0200 From: Kern Sibbald <kern@sibbald.com> To: "Justin T. Gibbs" <gibbs@scsiguy.com> Cc: mjacob@feral.com Subject: Re: SCSI tape data loss Message-ID: <1054670696.13606.302.camel@rufus> In-Reply-To: <955950000.1054667601@aslan.btc.adaptec.com> References: <3EDB31AB.16420.C8964B7D@localhost> <3EDB59A4.27599.C93270FB@localhost> <20030602110836.H71034@beppo> <20030602131225.F71034@beppo> <1054645616.13630.161.camel@rufus> <20030603072944.U44880@beppo> <1054652678.13630.209.camel@rufus> <882210000.1054657530@aslan.btc.adaptec.com> <1054658432.13630.252.camel@rufus> <900070000.1054659860@aslan.btc.adaptec.com> <1054660763.13630.279.camel@rufus> <955950000.1054667601@aslan.btc.adaptec.com>
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I cannot argue with what you write other than to
say that I generally use uint32_t for variables that
are positive integers, so I have them everywhere and
to change wlen to signed would lead to a flood of
changes of other variables. If I remember right one
thing that pushed me in this direction is the fact
that sizeof() is unsigned.
By the way, I've just completed a much simpler test
that I ask Dan to try to see if we can reproduce the
problem in a simpler case.
Best regards,
Kern
On Tue, 2003-06-03 at 21:13, Justin T. Gibbs wrote:
> >> > By the way, the funny casting is mandatory in C++,
> >> > because ssize_t as returned by the write is not the
> >> > same as size_t (what is written).
> >
> > If I remove the (uint32_t) cast, I get an error message:
> >
> > c++ -c -I. -I.. -g -O2 -Wall block.c
> > block.c: In function `int write_block_to_dev (JCR *, DEVICE *,
> > DEV_BLOCK *)':
> > block.c:381: warning: comparison between signed and unsigned integer
> > expressions
> >
> > Line 381 reads:
> >
> > if ((stat=write(dev->fd, block->buf, (size_t)wlen)) != wlen) {
> >
> > so I will stick with my funny casting.
> >
>
> This has nothing to do with type size or the fact that you are
> using C++. The same warning would occur when your code is
> compiled as C. wlen should be a signed type. Since wlen
> by definition cannot be larger than the largest positive integer
> reportable by the signed return value of write, using an unsigned
> type buys you nothing. Conversion from ssize_t to size_t will
> occur without error if you happen to chose to make wlen an ssize_t.
>
> I guess it matters little. My own philosophy is that casts should
> be used as a last resort rather than deployed indiscriminantly to
> cover up compile warnings. The above casts are easily avoidable
> which is why I mentioned them at all.
>
> --
> Justin
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