net/smc: add sysctl for max links per lgr for SMC-R v2.1

Add a new sysctl: net.smc.smcr_max_links_per_lgr, which is
used to control the preferred max links per lgr for SMC-R
v2.1. The default value of this sysctl is 2, and the acceptable
value ranges from 1 to 2.
Signed-off-by: Guangguan Wang <guangguan.wang@linux.alibaba.com>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/smc-sysctl.rst

@@ -57,3 +57,11 @@ rmem - INTEGER
 	only allowed 512KiB for SMC-R and 1MiB for SMC-D.
 
 	Default: 64KiB
+
+smcr_max_links_per_lgr - INTEGER
+	Controls the max number of links can be added to a SMC-R link group. Notice that
+	the actual number of the links added to a SMC-R link group depends on the number
+	of RDMA devices exist in the system. The acceptable value ranges from 1 to 2. Only
+	for SMC-R v2.1 and later.
+
+	Default: 2

include/net/netns/smc.h

@@ -22,5 +22,6 @@ struct netns_smc {
 	int				sysctl_smcr_testlink_time;
 	int				sysctl_wmem;
 	int				sysctl_rmem;
+	int				sysctl_max_links_per_lgr;
 };
 #endif

net/smc/af_smc.c

@@ -2461,7 +2461,7 @@ static void smc_listen_work(struct work_struct *work)
 	if (rc)
 		goto out_decl;
 
-	rc = smc_clc_srv_v2x_features_validate(pclc, ini);
+	rc = smc_clc_srv_v2x_features_validate(new_smc, pclc, ini);
 	if (rc)
 		goto out_decl;
 

net/smc/smc_clc.c

@@ -824,6 +824,7 @@ int smc_clc_send_proposal(struct smc_sock *smc, struct smc_init_info *ini)
 	struct smc_clc_smcd_gid_chid *gidchids;
 	struct smc_clc_msg_proposal_area *pclc;
 	struct smc_clc_ipv6_prefix *ipv6_prfx;
+	struct net *net = sock_net(&smc->sk);
 	struct smc_clc_v2_extension *v2_ext;
 	struct smc_clc_msg_smcd *pclc_smcd;
 	struct smc_clc_msg_trail *trl;
@@ -944,7 +945,7 @@ int smc_clc_send_proposal(struct smc_sock *smc, struct smc_init_info *ini)
 	if (smcr_indicated(ini->smc_type_v2)) {
 		memcpy(v2_ext->roce, ini->smcrv2.ib_gid_v2, SMC_GID_SIZE);
 		v2_ext->max_conns = SMC_CONN_PER_LGR_PREFER;
-		v2_ext->max_links = SMC_LINKS_PER_LGR_MAX_PREFER;
+		v2_ext->max_links = net->smc.sysctl_max_links_per_lgr;
 	}
 
 	pclc_base->hdr.length = htons(plen);
@@ -1171,10 +1172,12 @@ int smc_clc_send_accept(struct smc_sock *new_smc, bool srv_first_contact,
 	return len > 0 ? 0 : len;
 }
 
-int smc_clc_srv_v2x_features_validate(struct smc_clc_msg_proposal *pclc,
+int smc_clc_srv_v2x_features_validate(struct smc_sock *smc,
+				      struct smc_clc_msg_proposal *pclc,
 				      struct smc_init_info *ini)
 {
 	struct smc_clc_v2_extension *pclc_v2_ext;
+	struct net *net = sock_net(&smc->sk);
 
 	ini->max_conns = SMC_CONN_PER_LGR_MAX;
 	ini->max_links = SMC_LINKS_ADD_LNK_MAX;
@@ -1192,7 +1195,8 @@ int smc_clc_srv_v2x_features_validate(struct smc_clc_msg_proposal *pclc,
 		if (ini->max_conns < SMC_CONN_PER_LGR_MIN)
 			return SMC_CLC_DECL_MAXCONNERR;
 
-		ini->max_links = min_t(u8, pclc_v2_ext->max_links, SMC_LINKS_PER_LGR_MAX_PREFER);
+		ini->max_links = min_t(u8, pclc_v2_ext->max_links,
+				       net->smc.sysctl_max_links_per_lgr);
 		if (ini->max_links < SMC_LINKS_ADD_LNK_MIN)
 			return SMC_CLC_DECL_MAXLINKERR;
 	}

net/smc/smc_clc.h

@@ -422,7 +422,8 @@ int smc_clc_send_confirm(struct smc_sock *smc, bool clnt_first_contact,
 			 u8 version, u8 *eid, struct smc_init_info *ini);
 int smc_clc_send_accept(struct smc_sock *smc, bool srv_first_contact,
 			u8 version, u8 *negotiated_eid, struct smc_init_info *ini);
-int smc_clc_srv_v2x_features_validate(struct smc_clc_msg_proposal *pclc,
+int smc_clc_srv_v2x_features_validate(struct smc_sock *smc,
+				      struct smc_clc_msg_proposal *pclc,
 				      struct smc_init_info *ini);
 int smc_clc_clnt_v2x_features_validate(struct smc_clc_first_contact_ext *fce,
 				       struct smc_init_info *ini);

net/smc/smc_sysctl.c

@@ -25,6 +25,8 @@ static int max_sndbuf = INT_MAX / 2;
 static int max_rcvbuf = INT_MAX / 2;
 static const int net_smc_wmem_init = (64 * 1024);
 static const int net_smc_rmem_init = (64 * 1024);
+static int links_per_lgr_min = SMC_LINKS_ADD_LNK_MIN;
+static int links_per_lgr_max = SMC_LINKS_ADD_LNK_MAX;
 
 static struct ctl_table smc_table[] = {
 	{
@@ -68,6 +70,15 @@ static struct ctl_table smc_table[] = {
 		.extra1		= &min_rcvbuf,
 		.extra2		= &max_rcvbuf,
 	},
+	{
+		.procname	= "smcr_max_links_per_lgr",
+		.data		= &init_net.smc.sysctl_max_links_per_lgr,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &links_per_lgr_min,
+		.extra2		= &links_per_lgr_max,
+	},
 	{  }
 };
 
@@ -97,6 +108,7 @@ int __net_init smc_sysctl_net_init(struct net *net)
 	net->smc.sysctl_smcr_testlink_time = SMC_LLC_TESTLINK_DEFAULT_TIME;
 	WRITE_ONCE(net->smc.sysctl_wmem, net_smc_wmem_init);
 	WRITE_ONCE(net->smc.sysctl_rmem, net_smc_rmem_init);
+	net->smc.sysctl_max_links_per_lgr = SMC_LINKS_PER_LGR_MAX_PREFER;
 
 	return 0;
 

net/smc/smc_sysctl.h

@@ -23,6 +23,7 @@ void __net_exit smc_sysctl_net_exit(struct net *net);
 static inline int smc_sysctl_net_init(struct net *net)
 {
 	net->smc.sysctl_autocorking_size = SMC_AUTOCORKING_DEFAULT_SIZE;
+	net->smc.sysctl_max_links_per_lgr = SMC_LINKS_PER_LGR_MAX_PREFER;
 	return 0;
 }