I'm working on an implementation of SCSI RDMA Protocol (SRP) on InfiniBand, and I'm running into an issue managing the number of commands that get queued. The setup is like this: each SRP scsi_host can connect to multiple target ports. Each target port can have multiple LUNs behind it. To support this, for each connection, I create a device, set its parent to the scsi_host's shost_gendev, and then call scsi_scan_target to discover the LUNs behind the target port. This mostly works fine, except the number of outstanding commands is limited per connection. This doesn't fit that well with the Linux SCSI stack -- can_queue for the scsi_host doesn't work, since a single scsi_host can have multiple connections, and cmd_per_lun doesn't work since a single connection can have many LUNs. What seems like it _would_ be exactly what I need would be calling scsi_target_block() on the device representing the connection. Unfortunately, scsi_target_block() uses all sorts of device model stuff that takes semaphores and hence potentially sleeps. This means that I can't block a connection while holding a lock to prevent races. So I don't see a race-free way I can ensure that I never queue up too many commands on a given connection. Any advice? Thanks a lot, Roland - : 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
