答复: about print_disksize

"yangruifeng.09209@xxxxxxx" <yangruifeng.09209@xxxxxxx> · Fri, 9 Oct 2015 11:10:32 +0000

Steven，

	Thanks for your reply. I found a possible reason,

	+ /* Give size in megabytes (MB), not mebibytes (MiB). */ 
	+ /* We compute the exact rounded value, avoiding overflow. */ 
	+ printk (" (%ld MB)", (capacity - capacity/625 + 974)/1950);

	that is found in http://www.gossamer-threads.com/lists/linux/kernel/129337

Cheers

-----邮件原件-----
发件人: stgt-owner@xxxxxxxxxxxxxxx [mailto:stgt-owner@xxxxxxxxxxxxxxx] 代表 Steven Graf
发送时间: 2015年9月30日 20:40
收件人: yangruifeng 09209 (RD)
抄送: stgt@xxxxxxxxxxxxxxx; zhengbin 08747 (RD)
主题: Re: about print_disksize

Yang,

I believe your computation has over simplified the calculation taking place.  A megabyte is actually 1024 * 1024.  Furthermore the calculation is being run against an existing number so the result is the existing number expressed as MB.  Lastly the calculations seem very deliberate so my assumption is that there is some additional data is in band with the underlying data and needs to be stripped from the calculation.

Cheers,

-S

Sent from your iPhone

> On Sep 28, 2015, at 11:38 PM, "yangruifeng.09209@xxxxxxx" <yangruifeng.09209@xxxxxxx> wrote:
> 
> Hi All£¬
> 
> In print_disksize(target.c)
> mb = ((size / 512) - (((size / 512) / 625) - 974)) / 1950;
> 
> Why this? 
> 512¡¢625¡¢974¡¢1950 mean what?
> 
> Why not like this,
> Mb = size / (1000 * 1000)?Simpler and easier to understand
> 
> Thanks£¬
> Ruifeng Yang
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