UBUNTU: Add ubuntu-host module

ubuntu-host is a module for providing data to containers via proc.
Initially it is populated with a single file, esm-token, for
supplying ESM access tokens.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

ubuntu/Kconfig

@@ -14,6 +14,10 @@ source "ubuntu/hio/Kconfig"
 ##
 ##
 ##
+source "ubuntu/ubuntu-host/Kconfig"
+##
+##
+##
 ##
 ##
 ##

ubuntu/Makefile

@@ -19,6 +19,10 @@ obj-$(CONFIG_HIO)             += hio/
 ##
 ##
 ##
+obj-$(CONFIG_UBUNTU_HOST)      += ubuntu-host/
+##
+##
+##
 ifeq ($(ARCH),x86)
 obj-y				+= xr-usb-serial/
 endif

ubuntu/ubuntu-host/Kconfig

@@ -0,0 +1,5 @@
+config UBUNTU_HOST
+	tristate "proc dir for exporting host data to containers"
+	help
+	  Creates an ubuntu-host directory in proc for providing data from
+	  Ubuntu hosts to containers.

ubuntu/ubuntu-host/Makefile

@@ -0,0 +1 @@
+obj-$(CONFIG_UBUNTU_HOST) += ubuntu-host.o

ubuntu/ubuntu-host/ubuntu-host.c

@@ -0,0 +1,68 @@
+#include <linux/uaccess.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/proc_fs.h>
+#include <asm/uaccess.h>
+
+#define PROC_DIR		"ubuntu-host"
+
+#define ESM_TOKEN_FILE		"esm-token"
+#define ESM_TOKEN_MAX_SIZE		64
+
+static struct proc_dir_entry *proc_dir;
+static char esm_token_buffer[ESM_TOKEN_MAX_SIZE];
+
+static ssize_t esm_token_read(struct file *f, char __user *buf, size_t len,
+			      loff_t *off)
+{
+	return simple_read_from_buffer(buf, len, off, esm_token_buffer,
+				       strlen(esm_token_buffer));
+}
+
+static ssize_t esm_token_write(struct file *f, const char __user *buf,
+			       size_t len, loff_t *off)
+{
+	ssize_t ret;
+
+	if (len >= ESM_TOKEN_MAX_SIZE - 1)
+		return -EINVAL;
+
+	ret = simple_write_to_buffer(esm_token_buffer, ESM_TOKEN_MAX_SIZE - 1,
+				     off, buf, len);
+	if (ret >= 0)
+		esm_token_buffer[ret] = '\0';
+
+	return ret;
+}
+
+static const struct proc_ops esm_token_fops = {
+	.proc_read = esm_token_read,
+	.proc_write = esm_token_write,
+};
+
+static void ubuntu_host_cleanup(void)
+{
+	remove_proc_entry(ESM_TOKEN_FILE, proc_dir);
+	proc_remove(proc_dir);
+}
+
+static int __init ubuntu_host_init(void)
+{
+	proc_dir = proc_mkdir(PROC_DIR, NULL);
+	if (!proc_dir) {
+		pr_err("Failed to create ubuntu-host dir\n");
+		return -ENOMEM;
+	}
+
+	if (!proc_create_data(ESM_TOKEN_FILE, 0644, proc_dir, &esm_token_fops, NULL)) {
+		pr_err("Failed to create esm-tokan file\n");
+		ubuntu_host_cleanup();
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
+module_init(ubuntu_host_init);
+module_exit(ubuntu_host_cleanup);
+MODULE_LICENSE("GPL");