On Friday 26 October 2007 4:09:37 pm James Bottomley wrote: > On Fri, 2007-10-26 at 15:07 -0500, Rob Landley wrote: > > I don't understanding this code: > > > > 1) for echo "scsi add-single-device 0 1 2 3" > /proc/scsi/scsi, is this > > only for parallel scsi? > > No. > > > I thought most modern busses (usb, sata, FC, firewire, > > etc) dynamically assign these numbers and just use them as a unique > > identifier ala kdev_t. How would this work on one of the other devices? > > It's most often used to add or remove LUNs. Ok, I'm unclear on what a LUN is. All the devices I have lying around give me a LUN of zero. I used to think that a LUN was a bit like partition, and mostly used for CD changes. The structure "scsi_target" seems to aggregate host/channel/target and I thought it referred to a device. The earlier email between you, me, and Stefan, and myself said: James Bottomley said: > Stephan Richter said: > > "lun" is a target-wide unique number to address a logical unit on a > > target device. Its format is also a priori defined by the Linux SCSI > > low-level API. I think I understand that bit > > It is possible to transform "Logical Unit Identifiers" > > a.k.a. "Logical Unit Numbers" a.k.a. "LUNs" (which are either 8 bytes > > wide or 2 bytes wide) into the format of the lun. (Logical Unit > > Identifier is a property of all logical units of SCSI target devices.) This is something totally different, and seems a bit like a MAC address? > > The SCSI Architecture Model defines several different subspecies of 8 > > bytes wide LUNs. Some of these variants cannot be transformed lossless > > into the SCSI core's lun, but it appears that such variants of LUNs are > > not used in real hardware. > > Right, LUN has a specific transport independent meaning defined in SAM-3 > or SAM-4: > > http://www.t10.org/ftp/t10/drafts/sam3/sam3r14.pdf > http://www.t10.org/ftp/t10/drafts/sam4/sam4r13.pdf Unfortunately those two documents are 127 pages and 148 pages, respectively, and I haven't had a chance to make any headway in them yet. Every device I have that shows up as SCSI has shown up with a LUN of 0, which is target-wide unique because none of those targets have sub-functions that need to be independently addressed as devices. Is there an easy way to distinguish between "target-wide unique lun" and this Logical Unit Number device attribute that's either 8 bytes or 2 bytes wide? (Capitalization?) > > 2) How do you trigger this? /proc/scsi/scsi is read only even for root. > > root can still write to it. Wow. (Is this an idiosyncrasy of /proc, or a capability of root I've been unaware of all this time?) > > 3) This bit is repeated in both the add and remove logic: > > p = buffer + 23; > > > > host = simple_strtoul(p, &p, 0); > > channel = simple_strtoul(p + 1, &p, 0); > > id = simple_strtoul(p + 1, &p, 0); > > lun = simple_strtoul(p + 1, &p, 0); > > > > So what happens if you echo "scsi add-single-device 0" > /proc/scsi/scsi > > (or wherever file would trigger this function) so the read for channel > > skips over the null terminator (I'm assuming there is one) and reads who > > knows what? Or what if instead of ending that with one 0, you end it > > with enough zeroes to pad right up to PAGE_SIZE, so it reads the next > > page? (I don't even know what the page protections are on that, depends > > how > > __get_free_page(GFP_KERNEL) works...) > > > > Confused, > > It's relying on the user buffer being zero padded, but even if it isn't, > there's not much that can go wrong. It's also a deprecated interface. Where do I find out what interfaces are deprecated? (Is this written down somewhere? Or do you just mean that the whole of /proc is moving to /sys where possible?) > James Thanks (still confused), Rob -- "One of my most productive days was throwing away 1000 lines of code." - Ken Thompson. - 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
