linux-kernel - RE: [PATCH] block: create ioctl to discard-or-zeroout a range of blocks

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Date:	Thu, 12 Nov 2015 00:56:02 +0000
From:	"Seymour, Shane M" <shane.seymour@....com>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
CC:	Jens Axboe <axboe@...nel.dk>,
	Christoph Hellwig <hch@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
	Jeff Layton <jlayton@...chiereds.net>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	"martin.petersen@...cle.com" <martin.petersen@...cle.com>
Subject: RE: [PATCH] block: create ioctl to discard-or-zeroout a range of
 blocks

> which would make the other checks I suggested to ensure that neither start
> or end were more than (uint64_t)LLONG_MAX unnecessary.

My apologies I was wrong about what I said above - after thinking about it for longer you still need to make sure that at least len is not greater than (uint64_t)LLONG_MAX because in the calculation:

	if (start > (uint64_t)LLONG_MAX - len)
		return -EINVAL;

if len was more than (uint64_t)LLONG_MAX it would underflow and become a very large positive number and start would never be greater than that (and I said end when I should have said len).
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