On Wed, Jun 29, 2005 at 10:27:40AM -0700, Roland Dreier wrote: > 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. Just allocate one scsi_host per connection. - : 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
