Re: Advanced Format SAT devices show incorrect physical block size

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On Tue, 10 Jan 2017, Dainius Masiliūnas wrote:

> (I pressed reply instead of reply to all, sorry. Resending this.)
> 
> On Tue, Jan 10, 2017 at 8:29 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
> > There _is_ a quirk for broken models.  However, we don't know how
> > complete the set of quirk entries is, so we err on the side of caution.
> 
> Then what is it used for? There doesn't seem to be much point in a
> blacklist when the functionality is disabled by default to begin with.

It is used for preventing the kernel from issuing a READ CAPACITY(16) 
command to the device.  Normally the kernel would do this if the reply 
to READ CAPACITY(10) indicated there were more than 2^32 blocks (about 
2 TB).

> And if there's a whitelist, does it mean that we should submit the IDs
> of working USB devices for whitelisting? Also, is there a module
> parameter to toggle the functionality, to facilitate testing whether
> the device works fine or not?

There is no whitelist, but there is a quirk flag for devices that 
require READ CAPACITY(16) instead of READ CAPACITY(10) (because READ 
CAPACITY(10) returns incorrect information).

In theory, I suppose we could change the kernel so that it would 
default to READ CAPACITY(16) for devices that report a SCSI level >= 3, 
or something along those lines.  In general we hesitate to make changes 
of this sort, because they almost always end up breaking _some_ 
devices -- and if that happens then the change is reverted, with no 
exceptions.  Linus has a very strict rule about not breaking working 
systems.

Alan Stern

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