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

Jeff Garzik
2010-08-16T19:41:16Z

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@intel.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