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. 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. -- Lee Duncan -- 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
