Re: [usb-storage] Re: Make UAS work on HS for devices with and without command tagging support

Matthew Wilcox
2011-12-19T16:12:25Z

On Fri, Dec 16, 2011 at 10:47:39PM +0100, James Bottomley wrote:
> Well, no, what you want to do is use a shared tag map at the block
> level. That will manage a joint tag space for N queues without your
> having to partition it arbitrarily. see scsi_host_find_tag() and
> scsi_init_shared_tag_map().

By the way, the same verbiage about tags being shared across LUNs is also
present in the SAS spec (and various other specs last time I looked,
which wasn't recently). We should probably make this the default in
the SCSI core.

I suspect it hasn't bitten us because there are so few multi-LUN devices
out there, and it's only a "May" check, not "Must" check. But Linux is
technically in violation of the SAS spec by sending two commands to the
same target with the same tag.
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