Re: [ 38/48] SCSI & usb-storage: add try_rc_10_first flag
From: Matthew Wilcox
Date: Thu Jul 05 2012 - 23:05:23 EST
On Thu, Jul 05, 2012 at 05:40:45PM -0400, Alan Stern wrote:
> On Tue, 3 Jul 2012, Matthew Wilcox wrote:
> > I think the necessary algorithm is simpler than that:
> > Send RC10 (unless the device supports PI, in which case it's probably
> > enterprisey and well-tested)
> > Send RC16
> > If RC10 capacity agrees with RC16 capacity, use extra RC16 data.
> > (for values of "agrees with" that include the "-1 to use RC16" indicator)
> > Sure, it's one extra command, but really, who cares?
> Well, some USB devices might care. Right now we don't send RC16 to
> them at all because they get RC10 first and it indicates a capacity
> below 2 TB.
Mmm. I think I forgot a step:
Send RC10 (unless the device supports PI, in which case it's probably
enterprisey and well-tested)
If the device indicates a level < SPC_2, stop here
If RC10 capacity agrees with RC16 capacity, use extra RC16 data.
(for values of "agrees with" that include the "-1 to use RC16" indicator)
> In the end, usb-storage may be forced to use the NO_READ_CAPACITY_16
> flag with all devices except those we can positively identify as a
> USB-(S)ATA bridge.
Is that really an improvement over nobbling the IDENTIFY results to
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."
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