James Bottomley wrote: > On Thu, 2008-12-18 at 16:38 +0200, Boaz Harrosh wrote: >> OK Then I say D, go to T10, while white list the (0) devices that currently >> report !SCSI_3 but do support UNMAP. These are only USB right? >> >> Your tested devices report SCSI_3? Do all devices that are scsi_level > SCSI_2 >> suppose to support RC16? > > The problem isn't whether they support it or not. A proper standards > compliant SCSI device can be sent READ CAPACITY(16) and just return > ILLEGAL REQUEST sense quite normally. If those were all the devices in > the world, we'd send 16 first and fall back to 10. > > The problem is that there are devices (USB devices) that go haywire when > sent a READ CAPACITY 16 command (or, indeed, any other SCSI command not > in their vocabulary). It's for these devices that we do the 10->16 > dance the way we do in sd.c > > Our problem is to identify devices that could reliably receive (and this > doesn't mean process it just means return a standards compliant response > without crashing or going out to lunch) READ CAPACITY 16 because the > current Thin Provisioning draft requires this to indicate thin > provisioning support. > > My take is still that TP devices have to be SCSI-3 SBC-3 or higher, so > we just check this and for them do READ CAPACITY 16 with fallback to 10 > on ILLEGAL REQUEST return. USB has to whitelist the TP compliant > devices and not mangle the inquiry version field down to SCSI_2 for them > and the world will just work. > >> My point is make the standard, which is still a draft, crystal clear >> in a backward compatible way. All new, supporting, devices can be easily >> identified, and the very few devices that do support the new fixture but >> were released prior to the finalization of the draft be white-listed. >> And in any event don't let the standard be broken like that. > > James > > OK Jams Mathew thanks that makes sense. All these emulation layers being in HW, USB, or SW, libata will have to attempt an higher-then-SCSI_2 if they want RC16 stuff, full stop. That sounds safe to me, and the market will win. Boaz -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
