linux-kernel - Re: [PATCH v8 04/22] Change direct

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Date:	Thu, 31 Jul 2014 13:11:42 +0300
From:	Boaz Harrosh <openosd@...il.com>
To:	Matthew Wilcox <willy@...ux.intel.com>
CC:	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 04/22] Change direct_access calling convention

On 07/30/2014 10:45 PM, Matthew Wilcox wrote:
<>
>> + 	if (sector & (PAGE_SECTORS-1))
>> + 		return -EINVAL;
> 
> Mmm.  PAGE_SECTORS is private to brd (and also private to bcache!) at
> this point.  We've got a real mess of defines of SECTOR_SIZE, SECTORSIZE,
> SECTOR_SHIFT and so on, dotted throughout various random include files.
> I am not the river to flush those Augean stables today.
> 
> I'll go with this, from the dcssblk driver:
> 
>         if (sector % (PAGE_SIZE / 512))
>                 return -EINVAL;
> 

Sigh, right, sure I did not mean to make that fight. Works as well

<>
>> Style: Need a space between declaration and code (have you check-patch)
> 
> That's a bullshit check.  I don't know why it's in checkpatch.
> 

I did not invent the rules. But I do respect them. I think the merit
of sticking to some common style is much higher then any particular
style choice. Though this particular one I do like, because of the
C rule that forces all declarations before code, so it makes it easier
on the maintenance. In any way Maintainers are suppose to run checkpatch
before submission, some do ;-)

<>
>>> +	if (size < 0)
>>
>> 	if(size < PAGE_SIZE), No?
> 
> No, absolutely not.  PAGE_SIZE is unsigned long, which (if I understand
> my C integer promotions correctly) means that 'size' gets promoted to
> an unsigned long, and we compare them unsigned, so errors will never be
> caught by this check.

Good point I agree that you need a cast ie.

 	if(size < (long)PAGE_SIZE)

The reason I'm saying this is because of a bug I actually hit when
playing with partitioning and fdisk, it came out that the last partition's
size was not page aligned, and code that checked for (< 0) crashed because
prd returned the last two sectors of the partition, since your API is sector
based this can happen for you here, before you are memseting a PAGE_SIZE
you need to test there is space, No? 

> 
> 

Thanks
Boaz

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