Date: Tue, 10 Dec 2013 17:58:27 -0600 From: Nathan Whitehorn <nwhitehorn@freebsd.org> To: dgilbert@interlog.com, FreeBSD SCSI <freebsd-scsi@freebsd.org> Cc: Hannes Reinecke <hare@suse.de> Subject: Re: [CAM] Widening lun_id_t to 64-bits Message-ID: <52A7AAA3.5050404@freebsd.org> In-Reply-To: <52A7AA76.3060208@interlog.com> References: <52A7830B.2090803@freebsd.org> <52A7A69E.3030703@interlog.com> <52A7AA76.3060208@interlog.com>
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On 12/10/13 17:57, Douglas Gilbert wrote: > On 13-12-11 12:41 AM, Douglas Gilbert wrote: >> On 13-12-10 10:09 PM, Nathan Whitehorn wrote: >>> Modern SCSI hardware often uses 64-bit logical units (LUNs). The >>> patch found at >>> http://people.freebsd.org/~nwhitehorn/lun64.diff widens the type of >>> lun_id_t to >>> 64 bits, bumps CAM_VERSION, and begins exposing these to drivers >>> that are marked >>> as supporting extended LUNs. No behavior is changed except that >>> peripheral with >>> very long LUNs that didn't work before will start working. Binary >>> compatibility >>> with old code is also kept. There is, however, a chance that some >>> 3rd party >>> software might be unhappy about the type widening, so I'd appreciate >>> any testing >>> results. Barring any issues, I will commit this on Friday. >> >> Interesting, Hannes Reinecke is trying to do something >> very similar in the Linux SCSI subsystem. His patch set >> today will be the third attempt in a year (by my count) >> and he might just get over the top this time. There is >> some support in my sg3_utils package for the way Linux >> is implementing "64 bit LUNs". The sg3_utils package >> also supports FreeBSD so I'm interested in what your >> mapping will be. >> >> Now, as you are no doubt aware, SCSI (www.t10.org and specifically >> sam5r15.pdf) does not have 64 bit LUNs, it has 8 byte LUNs in >> SCSI order (i.e. big endian). Given that major architectures >> like i386 and x86_64 are little endian, the mapping between >> a 64 bit integer in native form and an 8 byte SCSI LUN is >> a bit of a puzzle. That becomes a little harder when you try >> for low numbered integers representing the T10 3 bit LUNs >> (showing my age), 8 bit LUNs and 16 bit LUNs. >> >> Down to brass tacks: what exactly will a SCSI REPORT LUNS >> WELL KNOWN LOGICAL UNIT number [T10 (in hex): c1 01 00 00 >> 00 00 00 00] be in one of your 64 bits LUNs? Will that be >> the same in little endian and big endian architectures? >> There is also the representation of that LUN in logs; for >> example lun=13907397124296802304 is not very intuitive. >> >> More examples would be great, perhaps from the 4, 6 and 8 byte >> "extended logical unit addressing format". >> >> >> Robert Elliott who has been a T10 technical editor has written >> a paper on this subject but google fails me, perhaps someone >> else can supply the url. His advice was too late for Linux >> and perhaps it is already too late for FreeBSD. > > The document I was trying to find was a www.t10.org proposal: > 06-003r1, see its overview for a rationale. The Logical Unit > Representation Format section was accepted and can be found > in sam5r15.pdf section 4.7.2 > > Doug Gilbert > > Ah, OK. That we are following. -Nathan
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