IB: add a proper completion queue abstraction

This adds an abstraction that allows ULPs to simply pass a completion
object and completion callback with each submitted WR and let the RDMA
core handle the nitty gritty details of how to handle completion
interrupts and poll the CQ.

In detail there is a new ib_cqe structure which just contains the
completion callback, and which can be used to get at the containing
object using container_of.  It is pointed to by the WR and WC as an
alternative to the wr_id field, similar to how many ULPs already use
the field to store a pointer using casts.

A driver using the new completion callbacks allocates it's CQs using
the new ib_create_cq API, which in addition to the number of CQEs and
the completion vectors also takes a mode on how we poll for CQEs.
Three modes are available: direct for drivers that never take CQ
interrupts and just poll for them, softirq to poll from softirq context
using the to be renamed blk-iopoll infrastructure which takes care of
rearming and budgeting, or a workqueue for consumer who want to be
called from user context.

Thanks a lot to Sagi Grimberg who helped reviewing the API, wrote
the current version of the workqueue code because my two previous
attempts sucked too much and converted the iSER initiator to the new
API.

Signed-off-by: Christoph Hellwig <hch@lst.de>

1 files changed, 35 insertions, 3 deletions

diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
index 9a68a19..131dd4b 100644
--- a/include/rdma/ib_verbs.h
+++ b/include/rdma/ib_verbs.h
@@ -49,6 +49,7 @@
 #include <linux/scatterlist.h>
 #include <linux/workqueue.h>
 #include <linux/socket.h>
+#include <linux/irq_poll.h>
 #include <uapi/linux/if_ether.h>
 
 #include <linux/atomic.h>
@@ -56,6 +57,7 @@
 #include <asm/uaccess.h>
 
 extern struct workqueue_struct *ib_wq;
+extern struct workqueue_struct *ib_comp_wq;
 
 union ib_gid {
 	u8	raw[16];
@@ -758,7 +760,10 @@ enum ib_wc_flags {
 };
 
 struct ib_wc {
-	u64			wr_id;
+	union {
+		u64		wr_id;
+		struct ib_cqe	*wr_cqe;
+	};
 	enum ib_wc_status	status;
 	enum ib_wc_opcode	opcode;
 	u32			vendor_err;
@@ -1079,9 +1084,16 @@ struct ib_mw_bind_info {
 	int		mw_access_flags;
 };
 
+struct ib_cqe {
+	void (*done)(struct ib_cq *cq, struct ib_wc *wc);
+};
+
 struct ib_send_wr {
 	struct ib_send_wr      *next;
-	u64			wr_id;
+	union {
+		u64		wr_id;
+		struct ib_cqe	*wr_cqe;
+	};
 	struct ib_sge	       *sg_list;
 	int			num_sge;
 	enum ib_wr_opcode	opcode;
@@ -1175,7 +1187,10 @@ static inline struct ib_sig_handover_wr *sig_handover_wr(struct ib_send_wr *wr)
 
 struct ib_recv_wr {
 	struct ib_recv_wr      *next;
-	u64			wr_id;
+	union {
+		u64		wr_id;
+		struct ib_cqe	*wr_cqe;
+	};
 	struct ib_sge	       *sg_list;
 	int			num_sge;
 };
@@ -1306,6 +1321,12 @@ struct ib_ah {
 
 typedef void (*ib_comp_handler)(struct ib_cq *cq, void *cq_context);
 
+enum ib_poll_context {
+	IB_POLL_DIRECT,		/* caller context, no hw completions */
+	IB_POLL_SOFTIRQ,	/* poll from softirq context */
+	IB_POLL_WORKQUEUE,	/* poll from workqueue */
+};
+
 struct ib_cq {
 	struct ib_device       *device;
 	struct ib_uobject      *uobject;
@@ -1314,6 +1335,12 @@ struct ib_cq {
 	void                   *cq_context;
 	int               	cqe;
 	atomic_t          	usecnt; /* count number of work queues */
+	enum ib_poll_context	poll_ctx;
+	struct ib_wc		*wc;
+	union {
+		struct irq_poll		iop;
+		struct work_struct	work;
+	};
 };
 
 struct ib_srq {
@@ -2453,6 +2480,11 @@ static inline int ib_post_recv(struct ib_qp *qp,
 	return qp->device->post_recv(qp, recv_wr, bad_recv_wr);
 }
 
+struct ib_cq *ib_alloc_cq(struct ib_device *dev, void *private,
+		int nr_cqe, int comp_vector, enum ib_poll_context poll_ctx);
+void ib_free_cq(struct ib_cq *cq);
+int ib_process_cq_direct(struct ib_cq *cq, int budget);
+
 /**
  * ib_create_cq - Creates a CQ on the specified device.
  * @device: The device on which to create the CQ.