Date: Sat, 21 Aug 1999 10:15:05 +0200 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: "Brian F. Feldman" <green@FreeBSD.org> Cc: cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/kern kern_physio.c Message-ID: <11805.935223305@critter.freebsd.dk> In-Reply-To: Your message of "Sat, 21 Aug 1999 00:50:52 PDT." <Pine.BSF.4.10.9908210046530.55604-100000@freefall.freebsd.org>
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In message <Pine.BSF.4.10.9908210046530.55604-100000@freefall.freebsd.org>, "Brian F. Feldman" writes:
>On Sat, 21 Aug 1999, Poul-Henning Kamp wrote:
>
>> >+ bp->b_blkno = blockno;
>> >+ if (bp->b_blkno != blockno) {
>> > ^- How can this comparison ever fail?
>>
>> They're different sizes.
>
>But you set bp->b_blkno to blockno, then compare whether or not they're
>equal. I'm pretty sure that's not right.
<CARDBOARD>
Assume for a moment that the uio_offset is 0x20000000000.
Shifting it down 9 places we get: 0x100000000, this goes into
blockno which is 64 bits wide: no worries.
Next we assign blockno to bp->b_blockno which is 32 bits wide,
what happens to the upper 32 bits ? They're ignored, so the
value of bp->b_blockno will be: 0x00000000.
Next we compare the two, are they the same ? No.
</CARDBOARD>
--
Poul-Henning Kamp FreeBSD coreteam member
phk@FreeBSD.ORG "Real hackers run -current on their laptop."
FreeBSD -- It will take a long time before progress goes too far!
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