linux-kernel - Re: [PATCH] 2.6.35 libata support for > 512 byte sectors (e.g. 4K Native)

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Date:	Mon, 16 Aug 2010 15:41:09 -0400
From:	Jeff Garzik <jgarzik@...ox.com>
To:	Grant Grundler <grundler@...gle.com>
CC:	"Wilcox, Matthew R" <matthew.r.wilcox@...el.com>,
	Tejun Heo <tj@...nel.org>,
	Linux IDE <linux-ide@...r.kernel.org>,
	Gwendal Grignou <gwendal@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] 2.6.35 libata support for > 512 byte sectors (e.g. 4K
 Native)

On 08/16/2010 03:17 PM, Grant Grundler wrote:
> On Sat, Aug 14, 2010 at 9:37 PM, Wilcox, Matthew R
> <matthew.r.wilcox@...el.com>  wrote:
>> If you will insist on sending to my Outlook address, you'll get replies in standard broken Outlook format.  You've been warned.
>
> You trumped my Gmail warning. I fold. :)
>
>>
>> ---
>>
>> +/* BUG: Big endian systems need accesses to "id" wrapped with le16_to_cpu().
>> + */
>>
>> No, it's already been converted.  See ata_dev_read_id().
>
> Ah - good. I'll remove the comment.
>
>>
>> I'm not sure about your use of a switch to set the sector size.  Have you checked the code that GCC generates for this?
>
> The switch probably sucks unless we could weight the order of the
> tests. E.g. common cases first. But it's just an implementation detail
> that is relatively easy to replace with the bitmap you had implemented
> before.
>
>>
>> All the places you dereference dev->sdev are within a callchain from ->queuecommand; sdev can't possibly go away.
>> It'd be clearer that this is the case if you used scmd->device->sector_size instead of dev->sdev->sector_size.
>
> Thank you - that looks much better to me too.
>
>> --
>>
>> @@ -516,7 +515,7 @@ int ata_cmd_ioctl(struct scsi_device *scsidev, void __user *arg)
>>         memset(scsi_cmd, 0, sizeof(scsi_cmd));
>>
>>         if (args[3]) {
>> -               argsize = SECTOR_SIZE * args[3];
>> +               argsize = ATA_SECT_SIZE * args[3];
>>                 argbuf = kmalloc(argsize, GFP_KERNEL);
>>                 if (argbuf == NULL) {
>>                         rc = -ENOMEM;
>>
>> I think this is wrong.  The ioctl does PIO Data-in; as such, it should use the native sector size, not 512.
>> That said, there's a possibility of data corruption for programs which use this ioctl, assuming a 512-byte sector size when it's natively 4k.
>> This one's tricky and needs serious thought.  I might error it if sector_size isn't 512 bytes :-)
>> It's a legacy ioctl anyway, right?
>
> I have no idea. If it's tricky, I probably have it wrong.
> Anyone else have guidance here?

The main question is whether the size of a DRQ block changes, when LBA 
logical size changes?  I need to review the ATA8 specs in this area, but 
I would think some interfaces that return 512-byte pages for things like 
SMART info would be unchanged.  How do the drives behave for 
PIO-Data-{In,Out} commands that are not reading/writing user data, but 
rather drive metadata?

	Jeff



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