On Mon, 12 Nov 2012, Paolo Bonzini wrote:
> Il 12/11/2012 16:10, James Bottomley ha scritto:
> >> Actually it only turns it on for large capacity drives, as said in the
> >> comment. sdp->force_read_16 only matters for >2TB drives:
> >
> > If you follow the discussion, we'll need to turn it on for some drives
> > regardless of size.
>
> Even if the two reasons to use r/w(16) commands were setting the same
> flag, it would be handled in a separate patch; it doesn't really make
> sense to complicate the code now when a one-liner does it.
>
> The proposed change is not part of the Oct 31st draft available on
> t10.org, for what we know the discussion could end up in nothing.
There's a simple way to do what everybody wants. Add a "use_16_for_rw"
flag with the understanding that it overrides use_10_for_rw, and set
this flag in sd_read_capacity() if the actual capacity is >= 2^32
blocks (as opposed to 2^41 bytes). Similarly, clear the flag if the
actual capacity is smaller -- a device with removable media might
require this, in theory.
Then the test in sd_prep_fn() becomes
if (sdp->use_16_for_rw) {
rather than
if (block > 0xffffffff) {
which on 32-bit architectures is a simpler test. If T10 decides to
deprecate the 10-byte commands then a second patch can set the new flag
(and avoid clearing it) under the appropriate circumstances.
Alan Stern
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