[RFC PATCH 4/4] sysctl: mqueue: Do not use dynamic memory

[Alexey Gladkov <legion@kernel.org>]

Dynamic memory allocation is needed to modify .data and specify the
per namespace parameter. The new sysctl API is allowed to get rid of
the need for such modification.

Signed-off-by: Alexey Gladkov <legion@kernel.org>
---
 include/linux/ipc_namespace.h |  17 -----
 ipc/mq_sysctl.c               | 138 +++++++++++++++++++---------------
 ipc/mqueue.c                  |   5 --
 ipc/namespace.c               |   6 --
 4 files changed, 79 insertions(+), 87 deletions(-)

diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h
index 51c2c247c447..d20753093a2c 100644
--- a/include/linux/ipc_namespace.h
+++ b/include/linux/ipc_namespace.h
@@ -174,21 +174,4 @@ static inline void put_ipc_ns(struct ipc_namespace *ns)
 }
 #endif
 
-#ifdef CONFIG_POSIX_MQUEUE_SYSCTL
-
-void retire_mq_sysctls(struct ipc_namespace *ns);
-bool setup_mq_sysctls(struct ipc_namespace *ns);
-
-#else /* CONFIG_POSIX_MQUEUE_SYSCTL */
-
-static inline void retire_mq_sysctls(struct ipc_namespace *ns)
-{
-}
-
-static inline bool setup_mq_sysctls(struct ipc_namespace *ns)
-{
-	return true;
-}
-
-#endif /* CONFIG_POSIX_MQUEUE_SYSCTL */
 #endif
diff --git a/ipc/mq_sysctl.c b/ipc/mq_sysctl.c
index fbf6a8b93a26..08ff7dfb721c 100644
--- a/ipc/mq_sysctl.c
+++ b/ipc/mq_sysctl.c
@@ -13,6 +13,45 @@
 #include <linux/capability.h>
 #include <linux/slab.h>
 
+static inline void *data_from_ns(struct ctl_context *ctx, struct ctl_table *table);
+
+static int mq_sys_open(struct ctl_context *ctx, struct inode *inode, struct file *file)
+{
+	ctx->ctl_data = current->nsproxy->ipc_ns;
+	return 0;
+}
+
+static ssize_t mq_sys_read(struct ctl_context *ctx, struct file *file,
+		     char *buffer, size_t *lenp, loff_t *ppos)
+{
+	struct ctl_table table = *ctx->table;
+	table.data = data_from_ns(ctx, ctx->table);
+	return table.proc_handler(&table, 0, buffer, lenp, ppos);
+}
+
+static ssize_t mq_sys_write(struct ctl_context *ctx, struct file *file,
+		      char *buffer, size_t *lenp, loff_t *ppos)
+{
+	struct ctl_table table = *ctx->table;
+	table.data = data_from_ns(ctx, ctx->table);
+	return table.proc_handler(&table, 1, buffer, lenp, ppos);
+}
+
+static struct ctl_fops mq_sys_fops = {
+	.open	= mq_sys_open,
+	.read	= mq_sys_read,
+	.write	= mq_sys_write,
+};
+
+enum {
+	MQ_SYSCTL_QUEUES_MAX,
+	MQ_SYSCTL_MSG_MAX,
+	MQ_SYSCTL_MSGSIZE_MAX,
+	MQ_SYSCTL_MSG_DEFAULT,
+	MQ_SYSCTL_MSGSIZE_DEFAULT,
+	MQ_SYSCTL_COUNTS
+};
+
 static int msg_max_limit_min = MIN_MSGMAX;
 static int msg_max_limit_max = HARD_MSGMAX;
 
@@ -20,14 +59,15 @@ static int msg_maxsize_limit_min = MIN_MSGSIZEMAX;
 static int msg_maxsize_limit_max = HARD_MSGSIZEMAX;
 
 static struct ctl_table mq_sysctls[] = {
-	{
+	[MQ_SYSCTL_QUEUES_MAX] = {
 		.procname	= "queues_max",
 		.data		= &init_ipc_ns.mq_queues_max,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec,
+		.ctl_fops	= &mq_sys_fops,
 	},
-	{
+	[MQ_SYSCTL_MSG_MAX] = {
 		.procname	= "msg_max",
 		.data		= &init_ipc_ns.mq_msg_max,
 		.maxlen		= sizeof(int),
@@ -35,8 +75,9 @@ static struct ctl_table mq_sysctls[] = {
 		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= &msg_max_limit_min,
 		.extra2		= &msg_max_limit_max,
+		.ctl_fops	= &mq_sys_fops,
 	},
-	{
+	[MQ_SYSCTL_MSGSIZE_MAX] = {
 		.procname	= "msgsize_max",
 		.data		= &init_ipc_ns.mq_msgsize_max,
 		.maxlen		= sizeof(int),
@@ -44,8 +85,9 @@ static struct ctl_table mq_sysctls[] = {
 		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= &msg_maxsize_limit_min,
 		.extra2		= &msg_maxsize_limit_max,
+		.ctl_fops	= &mq_sys_fops,
 	},
-	{
+	[MQ_SYSCTL_MSG_DEFAULT] = {
 		.procname	= "msg_default",
 		.data		= &init_ipc_ns.mq_msg_default,
 		.maxlen		= sizeof(int),
@@ -53,8 +95,9 @@ static struct ctl_table mq_sysctls[] = {
 		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= &msg_max_limit_min,
 		.extra2		= &msg_max_limit_max,
+		.ctl_fops	= &mq_sys_fops,
 	},
-	{
+	[MQ_SYSCTL_MSGSIZE_DEFAULT] = {
 		.procname	= "msgsize_default",
 		.data		= &init_ipc_ns.mq_msgsize_default,
 		.maxlen		= sizeof(int),
@@ -62,70 +105,47 @@ static struct ctl_table mq_sysctls[] = {
 		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= &msg_maxsize_limit_min,
 		.extra2		= &msg_maxsize_limit_max,
+		.ctl_fops	= &mq_sys_fops,
 	},
 	{}
 };
 
-static struct ctl_table_set *set_lookup(struct ctl_table_root *root)
+static inline void *data_from_ns(struct ctl_context *ctx, struct ctl_table *table)
 {
-	return &current->nsproxy->ipc_ns->mq_set;
+	struct ipc_namespace *ns = ctx->ctl_data;
+
+	switch (ctx->table - mq_sysctls) {
+		case MQ_SYSCTL_QUEUES_MAX:      return &ns->mq_queues_max;
+		case MQ_SYSCTL_MSG_MAX:         return &ns->mq_msg_max;
+		case MQ_SYSCTL_MSGSIZE_MAX:     return &ns->mq_msgsize_max;
+		case MQ_SYSCTL_MSG_DEFAULT:     return &ns->mq_msg_default;
+		case MQ_SYSCTL_MSGSIZE_DEFAULT: return &ns->mq_msgsize_default;
+	}
+	return NULL;
 }
 
-static int set_is_seen(struct ctl_table_set *set)
-{
-	return &current->nsproxy->ipc_ns->mq_set == set;
-}
+static struct ctl_table mq_sysctl_dir[] = {
+	{
+		.procname       = "mqueue",
+		.mode           = 0555,
+		.child          = mq_sysctls,
+	},
+	{}
+};
 
-static struct ctl_table_root set_root = {
-	.lookup = set_lookup,
+static struct ctl_table mq_sysctl_root[] = {
+	{
+		.procname       = "fs",
+		.mode           = 0555,
+		.child          = mq_sysctl_dir,
+	},
+	{}
 };
 
-bool setup_mq_sysctls(struct ipc_namespace *ns)
+static int __init mq_sysctl_init(void)
 {
-	struct ctl_table *tbl;
-
-	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);
-	}
-	if (!ns->mq_sysctls) {
-		kfree(tbl);
-		retire_sysctl_set(&ns->mq_set);
-		return false;
-	}
-
-	return true;
+	register_sysctl_table(mq_sysctl_root);
+	return 0;
 }
 
-void retire_mq_sysctls(struct ipc_namespace *ns)
-{
-	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);
-}
+device_initcall(mq_sysctl_init);
diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index c0f24cc9f619..ffb79a24d70b 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -1711,11 +1711,6 @@ static int __init init_mqueue_fs(void)
 	if (mqueue_inode_cachep == NULL)
 		return -ENOMEM;
 
-	if (!setup_mq_sysctls(&init_ipc_ns)) {
-		pr_warn("sysctl registration failed\n");
-		return -ENOMEM;
-	}
-
 	error = register_filesystem(&mqueue_fs_type);
 	if (error)
 		goto out_sysctl;
diff --git a/ipc/namespace.c b/ipc/namespace.c
index f760243ca685..ae83f0f2651b 100644
--- a/ipc/namespace.c
+++ b/ipc/namespace.c
@@ -59,10 +59,6 @@ static struct ipc_namespace *create_ipc_ns(struct user_namespace *user_ns,
 	if (err)
 		goto fail_put;
 
-	err = -ENOMEM;
-	if (!setup_mq_sysctls(ns))
-		goto fail_put;
-
 	sem_init_ns(ns);
 	msg_init_ns(ns);
 	shm_init_ns(ns);
@@ -129,8 +125,6 @@ static void free_ipc_ns(struct ipc_namespace *ns)
 	msg_exit_ns(ns);
 	shm_exit_ns(ns);
 
-	retire_mq_sysctls(ns);
-
 	dec_ipc_namespaces(ns->ucounts);
 	put_user_ns(ns->user_ns);
 	ns_free_inum(&ns->ns);
-- 
2.33.3