[PATCH net-next 10/15] net/smc: add operations to merge sndbuf with peer DMB

[Wen Gu]

In some scenarios using virtual ISM device, sndbuf can share the same
physical memory region with peer DMB to avoid data copy from one side
to the other. In such case the sndbuf is only a descriptor that
describes the shared memory and does not actually occupy memory, it's
more like a ghost buffer.

      +----------+                     +----------+
      | socket A |                     | socket B |
      +----------+                     +----------+
            |                               |
       +--------+                       +--------+
       | sndbuf |                       |  DMB   |
       |  desc  |                       |  desc  |
       +--------+                       +--------+
            |                               |
            |                          +----v-----+
            +-------------------------->  memory  |
                                       +----------+

So here introduces three new SMC-D device operations to check if this
feature is supported by device, and to {attach|detach} ghost sndbuf to
peer DMB. For now only loopback-ism supports this.

Signed-off-by: Wen Gu <guwen@xxxxxxxxxxxxxxxxx>
---
 include/net/smc.h |  3 +++
 net/smc/smc_ism.c | 40 ++++++++++++++++++++++++++++++++++++++++
 net/smc/smc_ism.h |  4 ++++
 3 files changed, 47 insertions(+)

diff --git a/include/net/smc.h b/include/net/smc.h
index 6273c3a8b24a..01387631d8a6 100644
--- a/include/net/smc.h
+++ b/include/net/smc.h
@@ -62,6 +62,9 @@ struct smcd_ops {
 	int (*register_dmb)(struct smcd_dev *dev, struct smcd_dmb *dmb,
 			    void *client);
 	int (*unregister_dmb)(struct smcd_dev *dev, struct smcd_dmb *dmb);
+	int (*support_dmb_nocopy)(struct smcd_dev *dev);
+	int (*attach_dmb)(struct smcd_dev *dev, struct smcd_dmb *dmb);
+	int (*detach_dmb)(struct smcd_dev *dev, u64 token);
 	int (*add_vlan_id)(struct smcd_dev *dev, u64 vlan_id);
 	int (*del_vlan_id)(struct smcd_dev *dev, u64 vlan_id);
 	int (*set_vlan_required)(struct smcd_dev *dev);
diff --git a/net/smc/smc_ism.c b/net/smc/smc_ism.c
index 4065ebd2e43d..2d2781724932 100644
--- a/net/smc/smc_ism.c
+++ b/net/smc/smc_ism.c
@@ -246,6 +246,46 @@ int smc_ism_register_dmb(struct smc_link_group *lgr, int dmb_len,
 	return rc;
 }
 
+bool smc_ism_support_dmb_nocopy(struct smcd_dev *smcd)
+{
+	/* for now only loopback-ism supports
+	 * merging sndbuf with peer DMB to avoid
+	 * data copies between them.
+	 */
+	return (smcd->ops->support_dmb_nocopy &&
+		smcd->ops->support_dmb_nocopy(smcd));
+}
+
+int smc_ism_attach_dmb(struct smcd_dev *dev, u64 token,
+		       struct smc_buf_desc *dmb_desc)
+{
+	struct smcd_dmb dmb;
+	int rc = 0;
+
+	if (!dev->ops->attach_dmb)
+		return -EINVAL;
+
+	memset(&dmb, 0, sizeof(dmb));
+	dmb.dmb_tok = token;
+	rc = dev->ops->attach_dmb(dev, &dmb);
+	if (!rc) {
+		dmb_desc->sba_idx = dmb.sba_idx;
+		dmb_desc->token = dmb.dmb_tok;
+		dmb_desc->cpu_addr = dmb.cpu_addr;
+		dmb_desc->dma_addr = dmb.dma_addr;
+		dmb_desc->len = dmb.dmb_len;
+	}
+	return rc;
+}
+
+int smc_ism_detach_dmb(struct smcd_dev *dev, u64 token)
+{
+	if (!dev->ops->detach_dmb)
+		return -EINVAL;
+
+	return dev->ops->detach_dmb(dev, token);
+}
+
 static int smc_nl_handle_smcd_dev(struct smcd_dev *smcd,
 				  struct sk_buff *skb,
 				  struct netlink_callback *cb)
diff --git a/net/smc/smc_ism.h b/net/smc/smc_ism.h
index 6903cd5d4d4d..8ea5ab737c6f 100644
--- a/net/smc/smc_ism.h
+++ b/net/smc/smc_ism.h
@@ -48,6 +48,10 @@ int smc_ism_put_vlan(struct smcd_dev *dev, unsigned short vlan_id);
 int smc_ism_register_dmb(struct smc_link_group *lgr, int buf_size,
 			 struct smc_buf_desc *dmb_desc);
 int smc_ism_unregister_dmb(struct smcd_dev *dev, struct smc_buf_desc *dmb_desc);
+bool smc_ism_support_dmb_nocopy(struct smcd_dev *smcd);
+int smc_ism_attach_dmb(struct smcd_dev *dev, u64 token,
+		       struct smc_buf_desc *dmb_desc);
+int smc_ism_detach_dmb(struct smcd_dev *dev, u64 token);
 int smc_ism_signal_shutdown(struct smc_link_group *lgr);
 void smc_ism_get_system_eid(u8 **eid);
 u16 smc_ism_get_chid(struct smcd_dev *dev);
-- 
2.32.0.3.g01195cf9f