Adding linux-usb and linux-hotplug to cc list, in case they wish to comment. Summary: I want to change SCSI host number so that it gets re-used, like disk index numbers, instead of always increasing. Please see below. On 10/14/2015 11:53 AM, James Bottomley wrote: > On Wed, 2015-10-14 at 11:34 -0700, Lee Duncan wrote: >> On 10/14/2015 06:55 AM, James Bottomley wrote: >>> On Wed, 2015-10-07 at 16:51 -0700, Lee Duncan wrote: >>>> Update the SCSI hosts module to use the ida_simple*() routines >>>> to manage its host_no index instead of an ATOMIC integer. This >>>> means that the SCSI host number will now be reclaimable. >>> >>> OK, but why would we want to do this? We do it for sd because our minor >>> space for the device nodes is very constrained, so packing is essential. >>> For HBAs, there's no device space density to worry about, they're >>> largely statically allocated at boot time and not reusing the numbers >>> allows easy extraction of hotplug items for the logs (quite useful for >>> USB) because each separate hotplug has a separate and monotonically >>> increasing host number. >>> >>> James >>> >> >> Good question, James. Apologies for not making the need clear. >> >> The iSCSI subsystem uses a host structure for discovery, then throws it >> away. So each time it does discovery it gets a new host structure. With >> the current approach, that number is ever increasing. It's only a matter >> of time until some user with a hundreds of disks and perhaps thousands >> of LUNs, that likes to do periodic discovery (think super-computers) >> will run out of host numbers. Or, worse yet, get a negative number >> number (because the value is signed right now). >> >> And this use case is a real one right now, by the way. > > Um, so even if you do discovery continuously, say one every second, it > still will take 68 years before we wrap the sign. > >> As you can see from the patch, it's a small amount of code to ensure >> that the host number management is handled more cleanly. > > Well, I'm a bit worried about the loss of a monotonically increasing > host number from the debugging perspective. Right now, if you look at > any log, hostX always refers to one and only one incarnation throughout > the system lifetime for any given value of X. With your patch, the > lowest host number gets continually reused ... probably for every hot > plug event. If the USB and other hotplug system people don't mind this, > I suppose I can live with it, but I'd like to hear their view before > making this change. > > James > > > > -- Lee Duncan SUSE Labs -- 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
