net/smc: Introduce a sysctl for setting SMC-R buffer type

This patch introduces the sysctl smcr_buf_type for setting
the type of SMC-R sndbufs and RMBs.

Valid values includes:

- SMCR_PHYS_CONT_BUFS, which means use physically contiguous
buffers for better performance and is the default value.

- SMCR_VIRT_CONT_BUFS, which means use virtually contiguous
buffers in case of physically contiguous memory is scarce.

- SMCR_MIXED_BUFS, which means first try to use physically
contiguous buffers. If not available, then use virtually
contiguous buffers.

Signed-off-by: Wen Gu <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

Documentation/networking/smc-sysctl.rst

···
 	know how/when to uncork their sockets.
 
 	Default: 64K
+
+smcr_buf_type - INTEGER
+        Controls which type of sndbufs and RMBs to use in later newly created
+        SMC-R link group. Only for SMC-R.
+
+        Default: 0 (physically contiguous sndbufs and RMBs)
+
+        Possible values:
+
+        - 0 - Use physically contiguous buffers
+        - 1 - Use virtually contiguous buffers
+        - 2 - Mixed use of the two types. Try physically contiguous buffers first.
+          If not available, use virtually contiguous buffers then.

include/net/netns/smc.h

···
 	struct ctl_table_header		*smc_hdr;
 #endif
 	unsigned int			sysctl_autocorking_size;
+	unsigned int			sysctl_smcr_buf_type;
 };
 #endif

net/smc/smc_core.h

···
 	SMC_LGR_ASYMMETRIC_LOCAL,	/* local has 1, peer 2 active RNICs */
 };
 
+enum smcr_buf_type {		/* types of SMC-R sndbufs and RMBs */
+	SMCR_PHYS_CONT_BUFS	= 0,
+	SMCR_VIRT_CONT_BUFS	= 1,
+	SMCR_MIXED_BUFS		= 2,
+};
+
 enum smc_llc_flowtype {
 	SMC_LLC_FLOW_NONE	= 0,
 	SMC_LLC_FLOW_ADD_LINK	= 2,

net/smc/smc_sysctl.c

···
 #include <net/net_namespace.h>
 
 #include "smc.h"
+#include "smc_core.h"
 #include "smc_sysctl.h"
 
 static struct ctl_table smc_table[] = {
···
 		.maxlen         = sizeof(unsigned int),
 		.mode           = 0644,
 		.proc_handler	= proc_douintvec,
+	},
+	{
+		.procname	= "smcr_buf_type",
+		.data		= &init_net.smc.sysctl_smcr_buf_type,
+		.maxlen		= sizeof(unsigned int),
+		.mode		= 0644,
+		.proc_handler	= proc_douintvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_TWO,
 	},
 	{  }
 };
···
 		goto err_reg;
 
 	net->smc.sysctl_autocorking_size = SMC_AUTOCORKING_DEFAULT_SIZE;
+	net->smc.sysctl_smcr_buf_type = SMCR_PHYS_CONT_BUFS;
 
 	return 0;