linux-kernel - Re: [PATCH 2/7] zram: Prevent overflow in logical block size

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Message-ID: <AANLkTim-Z_FCn7R_KRjfisKmR00ybrHYBxRSn8_uYF6F@mail.gmail.com>
Date:	Wed, 26 Jan 2011 21:14:57 +0200
From:	Pekka Enberg <penberg@...nel.org>
To:	Pekka Enberg <penberg@...nel.org>, Nitin Gupta <ngupta@...are.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Cc:	Robert Jennings <rcj@...ux.vnet.ibm.com>
Subject: Re: [PATCH 2/7] zram: Prevent overflow in logical block size

On Wed, Jan 26, 2011 at 9:09 PM, Robert Jennings <rcj@...ux.vnet.ibm.com> wrote:
> Pekka Enberg <penberg@...nel.org> wrote:
>> On Wed, Jan 26, 2011 at 7:23 PM, Robert Jennings <rcj@...ux.vnet.ibm.com> wrote:
>>> On a 64K page kernel, the value PAGE_SIZE passed to
>>> blk_queue_logical_block_size would overflow the logical block size
>>> argument (resulting in setting it to 0).
>>>
>>> Take the minimum of PAGE_SIZE or 4096 and use this for the block device
>>> logical block size.
>>>
>>> Signed-off-by: Robert Jennings <rcj@...ux.vnet.ibm.com>
>>> ---
>>>  drivers/staging/zram/zram_drv.c |    3 ++-
>>>  1 files changed, 2 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
>>> index d0e9e02..d5e0275 100644
>>> --- a/drivers/staging/zram/zram_drv.c
>>> +++ b/drivers/staging/zram/zram_drv.c
>>> @@ -621,7 +621,8 @@ static int create_device(struct zram *zram, int device_id)
>>>       * and n*PAGE_SIZED sized I/O requests.
>>>       */
>>>      blk_queue_physical_block_size(zram->disk->queue, PAGE_SIZE);
>>> -    blk_queue_logical_block_size(zram->disk->queue, PAGE_SIZE);
>>> +    blk_queue_logical_block_size(zram->disk->queue,
>>> +                    (unsigned short) min_t(unsigned int, PAGE_SIZE, 4096));
>>
>> I don't get it. No architecture supports PAGE_SIZE less than 4K so
>> that expression always ends up being 4096, no?
>
> Yes, I will cut out the min_t and just hard-code this to 4096.

Please make a ZRAM_BLOCK_SIZE constant or something for that.
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