[Devel] [PATCH rh7 v2 6/6] devtmpfs: lightweight virtualization

[Vladimir Davydov]

All this patch does is provides each VE with its own empty single tmpfs
mount, which appears on an attempt to mount "devtmpfs". It's up to the
userspace to populate this fs on container start, all kernel requests to
create a device node inside a VE are ignored.

Signed-off-by: Vladimir Davydov <vdavydov at parallels.com>
---
Changes in v2:
 - handle dev->class == NULL properly in devtmpfs_{create,delete}_node

 drivers/base/devtmpfs.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/ve.h      |  1 +
 kernel/ve/ve.c          |  4 +++
 3 files changed, 72 insertions(+)

diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c
index f59b7986ce08..daf97ee9b7bc 100644
--- a/drivers/base/devtmpfs.c
+++ b/drivers/base/devtmpfs.c
@@ -23,6 +23,7 @@
 #include <linux/ramfs.h>
 #include <linux/slab.h>
 #include <linux/kthread.h>
+#include <linux/ve.h>
 #include "base.h"
 
 static struct task_struct *thread;
@@ -53,9 +54,61 @@ static int __init mount_param(char *str)
 }
 __setup("devtmpfs.mount=", mount_param);
 
+#ifdef CONFIG_VE
+static int ve_test_dev_sb(struct super_block *s, void *p)
+{
+	return get_exec_env()->dev_sb == s;
+}
+
+static int ve_set_dev_sb(struct super_block *s, void *p)
+{
+	struct ve_struct *ve = get_exec_env();
+	int error;
+
+	error = set_anon_super(s, p);
+	if (!error) {
+		BUG_ON(ve->dev_sb);
+		ve->dev_sb = s;
+		atomic_inc(&s->s_active);
+	}
+	return error;
+}
+
+static struct dentry *ve_dev_mount(struct file_system_type *fs_type, int flags,
+		      const char *dev_name, void *data)
+{
+	int (*fill_super)(struct super_block *, void *, int);
+	struct super_block *s;
+	int error;
+
+#ifdef CONFIG_TMPFS
+	fill_super = shmem_fill_super;
+#else
+	fill_super = ramfs_fill_super;
+#endif
+	s = sget(fs_type, ve_test_dev_sb, ve_set_dev_sb, flags, NULL);
+	if (IS_ERR(s))
+		return ERR_CAST(s);
+
+	if (!s->s_root) {
+		error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
+		if (error) {
+			deactivate_locked_super(s);
+			return ERR_PTR(error);
+		}
+		s->s_flags |= MS_ACTIVE;
+	}
+	return dget(s->s_root);
+}
+#endif /* CONFIG_VE */
+
 static struct dentry *dev_mount(struct file_system_type *fs_type, int flags,
 		      const char *dev_name, void *data)
 {
+#ifdef CONFIG_VE
+	if (!ve_is_super(get_exec_env()))
+		return ve_dev_mount(fs_type, flags, dev_name, data);
+#endif
 #ifdef CONFIG_TMPFS
 	return mount_single(fs_type, flags, data, shmem_fill_super);
 #else
@@ -79,6 +132,16 @@ static inline int is_blockdev(struct device *dev)
 static inline int is_blockdev(struct device *dev) { return 0; }
 #endif
 
+#ifdef CONFIG_VE
+static inline int is_ve_dev(struct device *dev)
+{
+	return dev->class && dev->class->namespace == ve_namespace &&
+		ve_namespace(dev) != get_ve0();
+}
+#else
+static inline int is_ve_dev(struct device *dev) { return 0; }
+#endif
+
 int devtmpfs_create_node(struct device *dev)
 {
 	const char *tmp = NULL;
@@ -86,6 +149,8 @@ int devtmpfs_create_node(struct device *dev)
 
 	if (!thread)
 		return 0;
+	if (is_ve_dev(dev))
+		return 0;
 
 	req.mode = 0;
 	req.uid = GLOBAL_ROOT_UID;
@@ -125,6 +190,8 @@ int devtmpfs_delete_node(struct device *dev)
 
 	if (!thread)
 		return 0;
+	if (is_ve_dev(dev))
+		return 0;
 
 	req.name = device_get_devnode(dev, NULL, NULL, NULL, &tmp);
 	if (!req.name)
diff --git a/include/linux/ve.h b/include/linux/ve.h
index 84be82303c39..82a840a988b7 100644
--- a/include/linux/ve.h
+++ b/include/linux/ve.h
@@ -60,6 +60,7 @@ struct ve_struct {
 /* VE's root */
 	struct path		root_path;
 
+	struct super_block	*dev_sb;
 	struct super_block	*devpts_sb;
 
 #if IS_ENABLED(CONFIG_BINFMT_MISC)
diff --git a/kernel/ve/ve.c b/kernel/ve/ve.c
index 6699b83734b5..c2495acf9546 100644
--- a/kernel/ve/ve.c
+++ b/kernel/ve/ve.c
@@ -532,6 +532,10 @@ void ve_exit_ns(struct pid_namespace *pid_ns)
 	 * At this point all userspace tasks in container are dead.
 	 */
 
+	if (ve->dev_sb) {
+		deactivate_super(ve->dev_sb);
+		ve->dev_sb = NULL;
+	}
 	if (ve->devpts_sb) {
 		deactivate_super(ve->devpts_sb);
 		ve->devpts_sb = NULL;
-- 
2.1.4