Since the SCSI midlayer is moving towards entirely getting rid of
commands with use_sg == 0, we should treat this case as an exception.
Therefore, change the IB SRP initiator to create a fake scatterlist
for these commands with sg_init_one().  This simplifies the flow of
DMA mapping and unmapping, since SRP can just use dma_map_sg() and
dma_unmap_sg() unconditionally, rather than having to choose between
the dma_{map,unmap}_sg() and dma_{map,unmap}_single() variants.
Signed-off-by: NRoland Dreier <rolandd@cisco.com>

Convert srp_host->target_mutex from a semaphore to a mutex.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NRoland Dreier <rolandd@cisco.com>

Increase SRP max_luns to 512 to match the kernel's default, since SRP
storage targets can have lots of LUNs and the SRP initiator itself
doesn't have any particular limit.
Signed-off-by: NRoland Dreier <rolandd@cisco.com>

Add an InfiniBand SCSI RDMA Protocol (SRP) initiator.  This driver is
used to talk talk to InfiniBand SRP targets (storage devices).
Signed-off-by: NRoland Dreier <rolandd@cisco.com>