RDS doesn't support RDMA on memory apertures that require On Demand
Paging (ODP), such as FS DAX memory. A sysctl is added to indicate
whether RDMA requiring ODP is supported.

Reviewed-by: Håkon Bugge <redacted>
Reviewed-tested-by: Zhu Yanjun [off-list ref]
Signed-off-by: Hans Westgaard Ry <redacted>
Signed-off-by: Santosh Shilimkar <redacted>
 net/rds/ib.h        | 1 +
 net/rds/ib_sysctl.c | 8 ++++++++
 2 files changed, 9 insertions(+)

diff --git a/net/rds/ib.h b/net/rds/ib.h
index 67a715b..80e11ef 100644
+++ b/net/rds/ib.h

@@ -457,5 +457,6 @@ unsigned int rds_ib_stats_info_copy(struct rds_info_iterator *iter,
 extern unsigned long rds_ib_sysctl_max_unsig_bytes;
 extern unsigned long rds_ib_sysctl_max_recv_allocation;
 extern unsigned int rds_ib_sysctl_flow_control;
+extern unsigned int rds_ib_sysctl_odp_support;
 
 #endif

diff --git a/net/rds/ib_sysctl.c b/net/rds/ib_sysctl.c
index e4e41b3..7cc02cd 100644
+++ b/net/rds/ib_sysctl.c

@@ -60,6 +60,7 @@
  * will cause credits to be added before protocol negotiation.
  */
 unsigned int rds_ib_sysctl_flow_control = 0;
+unsigned int rds_ib_sysctl_odp_support;
 
 static struct ctl_table rds_ib_sysctl_table[] = {
 	{

@@ -103,6 +104,13 @@
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec,
 	},
+	{
+		.procname       = "odp_support",
+		.data           = &rds_ib_sysctl_odp_support,
+		.maxlen         = sizeof(rds_ib_sysctl_odp_support),
+		.mode           = 0444,
+		.proc_handler   = proc_dointvec,
+	},
 	{ }
 };