Filesystems visibility control group

1/1

index f37f872..b8189a4 100644
@@ -27,9 +27,214 @@
  *	Once the reference is obtained we can drop the spinlock.
  */
 
+/*
+ * the first three fields of it must coincide with the
+ * struct file_system_type
+ */
+
+struct file_system_proxy {
+	char *name;
+	struct file_system_proxy *next;
+	int fs_flags;
+	struct file_system_type *fs;
+};
+
 static struct file_system_type *file_systems;
 static DEFINE_RWLOCK(file_systems_lock);
 
+#ifdef CONFIG_CGROUP_FS
+#include <linux/cgroup.h>
+
+struct fs_cgroup {
+	struct cgroup_subsys_state css;
+
+	struct file_system_proxy *fs;
+};
+
+static inline struct fs_cgroup *css_to_fs(struct cgroup_subsys_state *ss)
+{
+	return container_of(ss, struct fs_cgroup, css);
+}
+
+static inline struct fs_cgroup *cgroup_to_fs(struct cgroup *c)
+{
+	return css_to_fs(cgroup_subsys_state(c, fs_subsys_id));
+}
+
+static inline struct file_system_type *task_fs_types(struct task_struct *t)
+{
+	struct cgroup_subsys_state *css;
+
+	css = task_subsys_state(t, fs_subsys_id);
+	if (css->cgroup->parent == NULL)
+		return file_systems;
+	else
+		return (struct file_system_type *)css_to_fs(css)->fs;
+}
+
+static struct cgroup_subsys_state *
+fs_create(struct cgroup_subsys *ss, struct cgroup *cont)
+{
+	struct fs_cgroup *fs;
+
+	fs = kzalloc(sizeof(struct fs_cgroup), GFP_KERNEL);
+	if (fs == NULL)
+		return ERR_PTR(-ENOMEM);
+	else
+		return &fs->css;
+}
+
+static void fs_destroy(struct cgroup_subsys *ss, struct cgroup *cont)
+{
+	struct fs_cgroup *fcg;
+	struct file_system_proxy *p, *next;
+
+	fcg = cgroup_to_fs(cont);
+
+	write_lock(&file_systems_lock);
+	for (p = fcg->fs; p != NULL; p = next) {
+		next = p->next;
+		put_filesystem(p->fs);
+		kfree(p);
+	}
+	write_unlock(&file_systems_lock);
+
+	kfree(fcg);
+}
+
+static ssize_t fs_write(struct cgroup *cont, struct cftype *cft,
+		struct file *f, const char __user *ubuf,
+		size_t nbytes, loff_t *pos)
+{
+	int err, add;
+	char buf[64];
+	struct file_system_type *fs;
+	struct file_system_proxy **p, *proxy = NULL;
+	struct fs_cgroup *fcg;
+
+	if (copy_from_user(buf, ubuf, sizeof(buf)))
+		return -EFAULT;
+
+	buf[sizeof(buf) - 1] = '\0';
+	if (buf[0] == '+')
+		add = 1;
+	else if (buf[0] == '-')
+		add = 0;
+	else
+		return -EINVAL;
+
+	if (add) {
+		err = -ENOMEM;
+		proxy = kmalloc(sizeof(*proxy) + sizeof(buf), GFP_KERNEL);
+		if (proxy == NULL)
+			goto err_alloc;
+	}
+
+	fcg = cgroup_to_fs(cont);
+	write_lock(&file_systems_lock);
+
+	for (p = &fcg->fs; *p != NULL; p = &(*p)->next)
+		if (strcmp((*p)->name, buf + 1) == 0)
+			goto fs_exists;
+
+	err = -ESRCH;
+	if (!add)
+		goto err_unlock;
+
+	for (fs = file_systems; fs != NULL; fs = fs->next)
+		if (strcmp(fs->name, buf + 1) == 0)
+			break;
+
+	if (fs == NULL)
+		goto err_srch;
+
+	if (!try_module_get(fs->owner))
+		goto err_srch;
+
+	proxy->name = (char *)(proxy + 1);
+	strcpy(proxy->name, fs->name);
+	proxy->fs_flags = fs->fs_flags | FS_IS_PROXY;
+	proxy->fs = fs;
+	proxy->next = fcg->fs;
+	fcg->fs = proxy;
+	write_unlock(&file_systems_lock);
+
+	return nbytes;
+
+fs_exists:
+	if (add) {
+		err = -EEXIST;
+		goto err_srch;
+	}
+
+	proxy = *p;
+	*p = proxy->next;
+	write_unlock(&file_systems_lock);
+	put_filesystem(proxy->fs);
+	kfree(proxy);
+	return nbytes;
+
+err_srch:
+	kfree(proxy);
+err_unlock:
+	write_unlock(&file_systems_lock);
+err_alloc:
+	return err;
+}
+
+static ssize_t fs_read(struct cgroup *cont, struct cftype *cft,
+		struct file *f, char __user *ubuf,
+		size_t nbytes, loff_t *pos)
+{
+	int len;
+	char *buf;
+	struct fs_cgroup *fcg;
+	struct file_system_proxy *p;
+
+	buf = (char *)__get_free_page(GFP_KERNEL);
+
+	len = 0;
+	fcg = cgroup_to_fs(cont);
+	read_lock(&file_systems_lock);
+	for (p = fcg->fs; p != NULL; p = p->next) {
+		if (len + strlen(p->name) > PAGE_SIZE)
+			break;
+
+		len += sprintf(buf + len, "%s\n", p->name);
+	}
+	read_unlock(&file_systems_lock);
+
+	return simple_read_from_buffer(ubuf, nbytes, pos, buf, len);
+}
+
+static struct cftype fs_files[] = {
+	{
+		.name = "list",
+		.write = fs_write,
+		.read = fs_read,
+	},
+};
+
+static int fs_populate(struct cgroup_subsys *ss, struct cgroup *cont)
+{
+	return cgroup_add_files(cont, ss,
+			fs_files, ARRAY_SIZE(fs_files));
+}
+
+struct cgroup_subsys fs_subsys = {
+	.name = "filesystems",
+	.subsys_id = fs_subsys_id,
+	.create = fs_create,
+	.destroy = fs_destroy,
+	.populate = fs_populate,
+};
+#else
+static inline struct file_system_type *task_fs_types(struct task_struct *t)
+{
+	return file_systems;
+}
+#endif
+
 /* WARNING: This can be used only if we _already_ own a reference */
 void get_filesystem(struct file_system_type *fs)
 {


Filesystems visibility control group

Pavel Emelyanov

Dave Hansen

Pavel Emelyanov

Serge E. Hallyn

Paul Jackson