IB/srp: Use FMRs to map gather/scatter lists

Create an SRP FMR pool on HCAs that support FMRs, and use FMRs to map
gather/scatter lists that have more than one entry into a single
memory region that appears virtually contiguous to the SRP target
(which is the RDMA initiator).

This patch bails out on FMR mapping for SCSI commands where the
gather/scatter list cannot be mapped into a single FMR because there
are sub-page-sized entries in middle of the list.  An unaligned
start or end of the list is OK.

Based on a patch by Vu Pham <vuhuong@mellanox.com>.
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/ulp/srp/ib_srp.h

@@ -46,6 +46,7 @@
 #include <rdma/ib_verbs.h>
 #include <rdma/ib_sa.h>
 #include <rdma/ib_cm.h>
+#include <rdma/ib_fmr_pool.h>
 
 enum {
 	SRP_PATH_REC_TIMEOUT_MS	= 1000,
@@ -62,7 +63,11 @@ enum {
 	SRP_SQ_SIZE		= SRP_RQ_SIZE - 1,
 	SRP_CQ_SIZE		= SRP_SQ_SIZE + SRP_RQ_SIZE,
 
-	SRP_TAG_TSK_MGMT	= 1 << (SRP_RQ_SHIFT + 1)
+	SRP_TAG_TSK_MGMT	= 1 << (SRP_RQ_SHIFT + 1),
+
+	SRP_FMR_SIZE		= 256,
+	SRP_FMR_POOL_SIZE	= 1024,
+	SRP_FMR_DIRTY_SIZE	= SRP_FMR_POOL_SIZE / 4
 };
 
 #define SRP_OP_RECV		(1 << 31)
@@ -77,15 +82,24 @@ enum srp_target_state {
 	SRP_TARGET_REMOVED
 };
 
-struct srp_host {
-	u8			initiator_port_id[16];
+struct srp_device {
+	struct list_head	dev_list;
 	struct ib_device       *dev;
-	u8                      port;
 	struct ib_pd	       *pd;
 	struct ib_mr	       *mr;
+	struct ib_fmr_pool     *fmr_pool;
+	int			fmr_page_shift;
+	int			fmr_page_size;
+	unsigned long		fmr_page_mask;
+};
+
+struct srp_host {
+	u8			initiator_port_id[16];
+	struct srp_device      *dev;
+	u8			port;
 	struct class_device	class_dev;
 	struct list_head	target_list;
-	struct mutex            target_mutex;
+	struct mutex		target_mutex;
 	struct completion	released;
 	struct list_head	list;
 };
@@ -95,6 +109,7 @@ struct srp_request {
 	struct scsi_cmnd       *scmnd;
 	struct srp_iu	       *cmd;
 	struct srp_iu	       *tsk_mgmt;
+	struct ib_pool_fmr     *fmr;
 	/*
 	 * Fake scatterlist used when scmnd->use_sg==0.  Can be killed
 	 * when the SCSI midlayer no longer generates non-SG commands.