[PATCH RFC 4/4] mqueue: Use sysctl context to register mq_sysctls

[Joel Granados <joel.granados@kernel.org>]

Replace the mq_sysctls array copy with a sysctl context kept in the
ctl_table_header. Flag each entry with CTL_TABLE_F_CTX_DATA to overlay
the ctl_table entry before calling the proc_handler.

Signed-off-by: Joel Granados <joel.granados@kernel.org>
---
 ipc/mq_sysctl.c | 44 ++++++++++----------------------------------
 1 file changed, 10 insertions(+), 34 deletions(-)

diff --git a/ipc/mq_sysctl.c b/ipc/mq_sysctl.c
index 0dd12e1c9f53ef07092ca3b638335a438d273a8c..9919e2d3a11a48a3e84c6c42d564e71dd60711da 100644
--- a/ipc/mq_sysctl.c
+++ b/ipc/mq_sysctl.c
@@ -11,7 +11,6 @@
 
 #include <linux/stat.h>
 #include <linux/capability.h>
-#include <linux/slab.h>
 #include <linux/cred.h>
 
 static int msg_max_limit_min = MIN_MSGMAX;
@@ -26,6 +25,7 @@ static const struct ctl_table mq_sysctls[] = {
 		.data		= &init_ipc_ns.mq_queues_max,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
+		.flags		= CTL_TABLE_F_CTX_DATA,
 		.proc_handler	= proc_dointvec,
 	},
 	{
@@ -33,6 +33,7 @@ static const struct ctl_table mq_sysctls[] = {
 		.data		= &init_ipc_ns.mq_msg_max,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
+		.flags		= CTL_TABLE_F_CTX_DATA,
 		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= &msg_max_limit_min,
 		.extra2		= &msg_max_limit_max,
@@ -42,6 +43,7 @@ static const struct ctl_table mq_sysctls[] = {
 		.data		= &init_ipc_ns.mq_msgsize_max,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
+		.flags		= CTL_TABLE_F_CTX_DATA,
 		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= &msg_maxsize_limit_min,
 		.extra2		= &msg_maxsize_limit_max,
@@ -51,6 +53,7 @@ static const struct ctl_table mq_sysctls[] = {
 		.data		= &init_ipc_ns.mq_msg_default,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
+		.flags		= CTL_TABLE_F_CTX_DATA,
 		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= &msg_max_limit_min,
 		.extra2		= &msg_max_limit_max,
@@ -60,6 +63,7 @@ static const struct ctl_table mq_sysctls[] = {
 		.data		= &init_ipc_ns.mq_msgsize_default,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
+		.flags		= CTL_TABLE_F_CTX_DATA,
 		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= &msg_maxsize_limit_min,
 		.extra2		= &msg_maxsize_limit_max,
@@ -116,39 +120,15 @@ static struct ctl_table_root set_root = {
 
 bool setup_mq_sysctls(struct ipc_namespace *ns)
 {
-	struct ctl_table *tbl;
+	struct sysctl_context ctx = SYSCTL_CTX(ns, &init_ipc_ns);
 
 	setup_sysctl_set(&ns->mq_set, &set_root, set_is_seen);
 
-	tbl = kmemdup(mq_sysctls, sizeof(mq_sysctls), GFP_KERNEL);
-	if (tbl) {
-		int i;
-
-		for (i = 0; i < ARRAY_SIZE(mq_sysctls); i++) {
-			if (tbl[i].data == &init_ipc_ns.mq_queues_max)
-				tbl[i].data = &ns->mq_queues_max;
-
-			else if (tbl[i].data == &init_ipc_ns.mq_msg_max)
-				tbl[i].data = &ns->mq_msg_max;
-
-			else if (tbl[i].data == &init_ipc_ns.mq_msgsize_max)
-				tbl[i].data = &ns->mq_msgsize_max;
-
-			else if (tbl[i].data == &init_ipc_ns.mq_msg_default)
-				tbl[i].data = &ns->mq_msg_default;
-
-			else if (tbl[i].data == &init_ipc_ns.mq_msgsize_default)
-				tbl[i].data = &ns->mq_msgsize_default;
-			else
-				tbl[i].data = NULL;
-		}
-
-		ns->mq_sysctls = __register_sysctl_table(&ns->mq_set,
-							 "fs/mqueue", tbl,
-							 ARRAY_SIZE(mq_sysctls));
-	}
+	ns->mq_sysctls = __register_sysctl_table_ctx(&ns->mq_set, "fs/mqueue",
+						     mq_sysctls,
+						     ARRAY_SIZE(mq_sysctls),
+						     &ctx);
 	if (!ns->mq_sysctls) {
-		kfree(tbl);
 		retire_sysctl_set(&ns->mq_set);
 		return false;
 	}
@@ -158,10 +138,6 @@ bool setup_mq_sysctls(struct ipc_namespace *ns)
 
 void retire_mq_sysctls(struct ipc_namespace *ns)
 {
-	const struct ctl_table *tbl;
-
-	tbl = ns->mq_sysctls->ctl_table_arg;
 	unregister_sysctl_table(ns->mq_sysctls);
 	retire_sysctl_set(&ns->mq_set);
-	kfree(tbl);
 }

-- 
2.50.1