sysfs_net_ipv4: Add sysfs-based knobs for controlling TCP window size

Add a family of knobs to /sys/kernel/ipv4 for controlling the TCP window size:

	tcp_wmem_min
	tcp_wmem_def
	tcp_wmem_max
	tcp_rmem_min
	tcp_rmem_def
	tcp_rmem_max

This six values mirror the sysctl knobs in /proc/sys/net/ipv4/tcp_wmem and
/proc/sys/net/ipv4/tcp_rmem.

Sysfs, unlike sysctl, allows us to set and manage the files' permissions and
owners.

Signed-off-by: Robert Love <rlove@google.com>

2 files changed, 89 insertions, 0 deletions

diff --git a/net/ipv4/Makefile b/net/ipv4/Makefile
index 80ff87ce43aa..6a13dce23c4c 100644
--- a/net/ipv4/Makefile
+++ b/net/ipv4/Makefile
@@ -14,6 +14,7 @@ obj-y     := route.o inetpeer.o protocol.o \
 	     inet_fragment.o
 
 obj-$(CONFIG_SYSCTL) += sysctl_net_ipv4.o
+obj-$(CONFIG_SYSFS) += sysfs_net_ipv4.o
 obj-$(CONFIG_IP_FIB_HASH) += fib_hash.o
 obj-$(CONFIG_IP_FIB_TRIE) += fib_trie.o
 obj-$(CONFIG_PROC_FS) += proc.o
diff --git a/net/ipv4/sysfs_net_ipv4.c b/net/ipv4/sysfs_net_ipv4.c
new file mode 100644
index 000000000000..0cbbf10026a6
--- /dev/null
+++ b/net/ipv4/sysfs_net_ipv4.c
@@ -0,0 +1,88 @@
+/*
+ * net/ipv4/sysfs_net_ipv4.c
+ *
+ * sysfs-based networking knobs (so we can, unlike with sysctl, control perms)
+ *
+ * Copyright (C) 2008 Google, Inc.
+ *
+ * Robert Love <rlove@google.com>
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/kobject.h>
+#include <linux/string.h>
+#include <linux/sysfs.h>
+#include <linux/init.h>
+#include <net/tcp.h>
+
+#define CREATE_IPV4_FILE(_name, _var) \
+static ssize_t _name##_show(struct kobject *kobj, \
+			    struct kobj_attribute *attr, char *buf) \
+{ \
+	return sprintf(buf, "%d\n", _var); \
+} \
+static ssize_t _name##_store(struct kobject *kobj, \
+			     struct kobj_attribute *attr, \
+			     const char *buf, size_t count) \
+{ \
+	int val, ret; \
+	ret = sscanf(buf, "%d", &val); \
+	if (ret != 1) \
+		return -EINVAL; \
+	if (val < 0) \
+		return -EINVAL; \
+	_var = val; \
+	return count; \
+} \
+static struct kobj_attribute _name##_attr = \
+	__ATTR(_name, 0644, _name##_show, _name##_store)
+
+CREATE_IPV4_FILE(tcp_wmem_min, sysctl_tcp_wmem[0]);
+CREATE_IPV4_FILE(tcp_wmem_def, sysctl_tcp_wmem[1]);
+CREATE_IPV4_FILE(tcp_wmem_max, sysctl_tcp_wmem[2]);
+
+CREATE_IPV4_FILE(tcp_rmem_min, sysctl_tcp_rmem[0]);
+CREATE_IPV4_FILE(tcp_rmem_def, sysctl_tcp_rmem[1]);
+CREATE_IPV4_FILE(tcp_rmem_max, sysctl_tcp_rmem[2]);
+
+static struct attribute *ipv4_attrs[] = {
+	&tcp_wmem_min_attr.attr,
+	&tcp_wmem_def_attr.attr,
+	&tcp_wmem_max_attr.attr,
+	&tcp_rmem_min_attr.attr,
+	&tcp_rmem_def_attr.attr,
+	&tcp_rmem_max_attr.attr,
+	NULL
+};
+
+static struct attribute_group ipv4_attr_group = {
+	.attrs = ipv4_attrs,
+};
+
+static __init int sysfs_ipv4_init(void)
+{
+	struct kobject *ipv4_kobject;
+	int ret;
+
+	ipv4_kobject = kobject_create_and_add("ipv4", kernel_kobj);
+	if (!ipv4_kobject)
+		return -ENOMEM;
+
+	ret = sysfs_create_group(ipv4_kobject, &ipv4_attr_group);
+	if (ret) {
+		kobject_put(ipv4_kobject);
+		return ret;
+	}
+
+	return 0;
+}
+
+subsys_initcall(sysfs_ipv4_init);