On Mon, Nov 12, 2012 at 10:10 AM, James Bottomley
<James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, 2012-11-12 at 15:31 +0100, Paolo Bonzini wrote:
>> Il 12/11/2012 12:33, James Bottomley ha scritto:
>> > On Fri, 2012-11-09 at 11:08 -0500, Jason J. Herne wrote:
>> >> diff --git a/drivers/usb/storage/scsiglue.c
>> >> b/drivers/usb/storage/scsiglue.c
>> >> index 13b8bcd..6ff785e 100644
>> >> --- a/drivers/usb/storage/scsiglue.c
>> >> +++ b/drivers/usb/storage/scsiglue.c
>> >> @@ -251,6 +251,11 @@ static int slave_configure(struct scsi_device
>> >> *sdev)
>> >> US_FL_SCM_MULT_TARG)) &&
>> >> us->protocol == USB_PR_BULK)
>> >> us->use_last_sector_hacks = 1;
>> >> +
>> >> + /* Force read-16 for large capacity drives. */
>> >> + sdev->force_read_16 = 1;
>> >> +
>> >> +
>> >
>> > This turns READ_16 on unconditionally for all USB disks ... is that
>> > safe? As in have you tested this with older USB thumb drives?
>>
>> 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.
>
>> >> + /* Many large capacity USB drives/controllers require the use of read(16). */
>> >> + force_read16 = (sdkp->capacity > 0xffffffffULL && sdp->force_read_16);
>> >> +
>> >> if (host_dif == SD_DIF_TYPE2_PROTECTION) {
>> >> SCpnt->cmnd = mempool_alloc(sd_cdb_pool, GFP_ATOMIC);
>> >>
>> >> @@ -833,7 +836,7 @@ static int sd_prep_fn(struct request_queue *q, struct request *rq)
>> >> SCpnt->cmnd[29] = (unsigned char) (this_count >> 16) & 0xff;
>> >> SCpnt->cmnd[30] = (unsigned char) (this_count >> 8) & 0xff;
>> >> SCpnt->cmnd[31] = (unsigned char) this_count & 0xff;
>> >> - } else if (block > 0xffffffff) {
>> >> + } else if (block > 0xffffffff || force_read16) {
>>
>> so the better name would be never_use_10_for_rw_on_large_disks. For
>> some definitions of better. :)
>
> Hm.
>
>> Any reason not to do this always on >2TB drives, which basically means
>> changing this:
>>
>> - } else if (block > 0xffffffff) {
>> + } else if (sdkp->capacity > 0xffffffff) {
>>
>> and nothing else?
>
> Because of the coming T10 mandate in SBC-4 deprecating everything other
> than the 16 byte commands.
>
It seems like the deprecations in the coming SBC-4 spec (still in
draft state, yes?) are a
separate issue best handled with a separate patch. My goal with this
patch is to allow Linux
to work with some (most/all?) large capacity drives in external USB
enclosures. The one line
solution proposed by Paolo accomplishes this goal while minimizing
code changes that
might need to be revised/undone later when the deprecation of
read/write(<16) is being
handled.
--
- Jason J. Herne (hernejj@xxxxxxxxx)
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