[PATCH 5/16] Make proc be mountable from different pid namespaces

[Pavel Emelianov <xemul@openvz.org>]

Each pid namespace should have the proc_mnt pointer even when
there's no user mounts to make proc_flush_task() work. To do
this we call the kern_mount() to obtain the proc mount point.

Since the current pid_namespace during this call is not the
newly created one we use the introduced MS_KERNMOUNT flag
to pass the namespace pointer to the proc_get_sb() call.

Signed-off-by: Pavel Emelianov <xemul@openvz.org>

---

 fs/proc/inode.c               |   20 +++++--
 fs/proc/internal.h            |    2 
 fs/proc/root.c                |  116 ++++++++++++++++++++++++++++++++++++++++--
 include/linux/pid_namespace.h |    3 +
 include/linux/proc_fs.h       |   15 +++++
 5 files changed, 147 insertions(+), 9 deletions(-)

diff -upr linux-2.6.22-rc4-mm2.orig/fs/proc/inode.c linux-2.6.22-rc4-mm2-2/fs/proc/inode.c
--- linux-2.6.22-rc4-mm2.orig/fs/proc/inode.c	2007-06-14 12:14:29.000000000 +0400
+++ linux-2.6.22-rc4-mm2-2/fs/proc/inode.c	2007-07-04 19:00:38.000000000 +0400
@@ -16,6 +16,7 @@
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/smp_lock.h>
+#include <linux/pid_namespace.h>
 
 #include <asm/system.h>
 #include <asm/uaccess.h>
@@ -429,9 +430,17 @@ out_mod:
 	return NULL;
 }			
 
-int proc_fill_super(struct super_block *s, void *data, int silent)
+int proc_fill_super(struct super_block *s, struct pid_namespace *ns)
 {
 	struct inode * root_inode;
+	struct proc_dir_entry * root_dentry;
+
+	root_dentry = &proc_root;
+	if (ns != &init_pid_ns) {
+		root_dentry = create_proc_root();
+		if (root_dentry == NULL)
+			goto out_no_de;
+	}
 
 	s->s_flags |= MS_NODIRATIME | MS_NOSUID | MS_NOEXEC;
 	s->s_blocksize = 1024;
@@ -440,8 +449,8 @@ int proc_fill_super(struct super_block *
 	s->s_op = &proc_sops;
 	s->s_time_gran = 1;
 	
-	de_get(&proc_root);
-	root_inode = proc_get_inode(s, PROC_ROOT_INO, &proc_root);
+	de_get(root_dentry);
+	root_inode = proc_get_inode(s, PROC_ROOT_INO, root_dentry);
 	if (!root_inode)
 		goto out_no_root;
 	root_inode->i_uid = 0;
@@ -452,9 +461,10 @@ int proc_fill_super(struct super_block *
 	return 0;
 
 out_no_root:
-	printk("proc_read_super: get root inode failed\n");
 	iput(root_inode);
-	de_put(&proc_root);
+	de_put(root_dentry);
+out_no_de:
+	printk("proc_read_super: get root inode failed\n");
 	return -ENOMEM;
 }
 MODULE_LICENSE("GPL");
diff -upr linux-2.6.22-rc4-mm2.orig/fs/proc/internal.h linux-2.6.22-rc4-mm2-2/fs/proc/internal.h
--- linux-2.6.22-rc4-mm2.orig/fs/proc/internal.h	2007-06-14 12:14:29.000000000 +0400
+++ linux-2.6.22-rc4-mm2-2/fs/proc/internal.h	2007-07-04 19:00:38.000000000 +0400
@@ -71,3 +71,5 @@ static inline int proc_fd(struct inode *
 {
 	return PROC_I(inode)->fd;
 }
+
+struct proc_dir_entry * create_proc_root(void);
diff -upr linux-2.6.22-rc4-mm2.orig/fs/proc/root.c linux-2.6.22-rc4-mm2-2/fs/proc/root.c
--- linux-2.6.22-rc4-mm2.orig/fs/proc/root.c	2007-06-14 12:14:29.000000000 +0400
+++ linux-2.6.22-rc4-mm2-2/fs/proc/root.c	2007-07-04 19:00:39.000000000 +0400
@@ -18,32 +18,89 @@
 #include <linux/bitops.h>
 #include <linux/smp_lock.h>
 #include <linux/mount.h>
+#include <linux/pid_namespace.h>
 
 #include "internal.h"
 
 struct proc_dir_entry *proc_net, *proc_net_stat, *proc_bus, *proc_root_fs, *proc_root_driver;
 
+static int proc_test_super(struct super_block *sb, void *data)
+{
+	return sb->s_fs_info == data;
+}
+
+static int proc_set_super(struct super_block *sb, void *data)
+{
+	struct pid_namespace *ns;
+
+	ns = (struct pid_namespace *)data;
+	sb->s_fs_info = get_pid_ns(ns);
+	return set_anon_super(sb, NULL);
+}
+
 static int proc_get_sb(struct file_system_type *fs_type,
 	int flags, const char *dev_name, void *data, struct vfsmount *mnt)
 {
+	int err;
+	struct super_block *sb;
+	struct pid_namespace *ns;
+	struct proc_inode *ei;
+
 	if (proc_mnt) {
 		/* Seed the root directory with a pid so it doesn't need
 		 * to be special in base.c.  I would do this earlier but
 		 * the only task alive when /proc is mounted the first time
 		 * is the init_task and it doesn't have any pids.
 		 */
-		struct proc_inode *ei;
 		ei = PROC_I(proc_mnt->mnt_sb->s_root->d_inode);
 		if (!ei->pid)
 			ei->pid = find_get_pid(1);
 	}
-	return get_sb_single(fs_type, flags, data, proc_fill_super, mnt);
+
+	if (flags & MS_KERNMOUNT)
+		ns = (struct pid_namespace *)data;
+	else
+		ns = current->nsproxy->pid_ns;
+
+	sb = sget(fs_type, proc_test_super, proc_set_super, ns);
+	if (IS_ERR(sb))
+		return PTR_ERR(sb);
+
+	if (!sb->s_root) {
+		sb->s_flags = flags;
+		err = proc_fill_super(sb, ns);
+		if (err) {
+			up_write(&sb->s_umount);
+			deactivate_super(sb);
+			return err;
+		}
+
+		ei = PROC_I(sb->s_root->d_inode);
+		if (!ei->pid)
+			ei->pid = find_get_pid(1);
+		sb->s_flags |= MS_ACTIVE;
+
+		mntput(ns->proc_mnt);
+		ns->proc_mnt = mnt;
+	}
+
+	return simple_set_mnt(mnt, sb);
+}
+
+static void proc_kill_sb(struct super_block *sb)
+{
+	struct pid_namespace *ns;
+
+	ns = (struct pid_namespace *)sb->s_fs_info;
+	kill_anon_super(sb);
+	if (ns != NULL)
+		put_pid_ns(ns);
 }
 
 static struct file_system_type proc_fs_type = {
 	.name		= "proc",
 	.get_sb		= proc_get_sb,
-	.kill_sb	= kill_anon_super,
+	.kill_sb	= proc_kill_sb,
 };
 
 void __init proc_root_init(void)
@@ -60,6 +117,7 @@ void __init proc_root_init(void)
 		unregister_filesystem(&proc_fs_type);
 		return;
 	}
+
 	proc_misc_init();
 	proc_net = proc_mkdir("net", NULL);
 	proc_net_stat = proc_mkdir("net/stat", NULL);
@@ -153,6 +211,58 @@ struct proc_dir_entry proc_root = {
 	.parent		= &proc_root,
 };
 
+/*
+ * creates the proc root entry for different proc trees
+ */
+
+struct proc_dir_entry * create_proc_root(void)
+{
+	struct proc_dir_entry *de;
+
+	de = kzalloc(sizeof(struct proc_dir_entry), GFP_KERNEL);
+	if (de != NULL) {
+		de->low_ino = PROC_ROOT_INO;
+		de->namelen = 5;
+		de->name = "/proc";
+		de->mode = S_IFDIR | S_IRUGO | S_IXUGO;
+		de->nlink = 2;
+		de->proc_iops = &proc_root_inode_operations;
+		de->proc_fops = &proc_root_operations;
+		de->parent = de;
+	}
+	return de;
+}
+
+int pid_ns_prepare_proc(struct pid_namespace *ns)
+{
+	struct vfsmount *mnt;
+
+	mnt = kern_mount_data(&proc_fs_type, ns);
+	if (!IS_ERR(mnt))
+		/*
+		 * do not save the reference from the proc super
+		 * block to the namespace. otherwise we will get
+		 * a circular reference ns->proc_mnt->mnt_sb->ns
+		 */
+		put_pid_ns(ns);
+	return 0;
+}
+
+void pid_ns_release_proc(struct pid_namespace *ns)
+{
+	struct vfsmount *mnt;
+
+	mnt = ns->proc_mnt;
+	/*
+	 * do not put the namespace reference as it wa not get in
+	 * pid_ns_prepare_proc(). safe to set NULL here as this
+	 * namespace is already dead and all the proc mounts are
+	 * released so nobudo will se this super block
+	 */
+	mnt->mnt_sb->s_fs_info = NULL;
+	mntput(mnt);
+}
+
 EXPORT_SYMBOL(proc_symlink);
 EXPORT_SYMBOL(proc_mkdir);
 EXPORT_SYMBOL(create_proc_entry);
diff -upr linux-2.6.22-rc4-mm2.orig/include/linux/pid_namespace.h linux-2.6.22-rc4-mm2-2/include/linux/pid_namespace.h
--- linux-2.6.22-rc4-mm2.orig/include/linux/pid_namespace.h	2007-06-14 12:14:29.000000000 +0400
+++ linux-2.6.22-rc4-mm2-2/include/linux/pid_namespace.h	2007-07-04 19:00:39.000000000 +0400
@@ -16,6 +15,9 @@ struct pidmap {
 	struct task_struct *child_reaper;
 	struct kmem_cache *pid_cachep;
 	struct pid_namespace *parent;
+#ifdef CONFIG_PROC_FS
+	struct vfsmount *proc_mnt;
+#endif
 };
 
 extern struct pid_namespace init_pid_ns;
diff -upr linux-2.6.22-rc4-mm2.orig/include/linux/proc_fs.h linux-2.6.22-rc4-mm2-2/include/linux/proc_fs.h
--- linux-2.6.22-rc4-mm2.orig/include/linux/proc_fs.h	2007-06-14 12:14:29.000000000 +0400
+++ linux-2.6.22-rc4-mm2-2/include/linux/proc_fs.h	2007-07-04 19:00:38.000000000 +0400
@@ -126,7 +126,8 @@ extern struct proc_dir_entry *create_pro
 extern void remove_proc_entry(const char *name, struct proc_dir_entry *parent);
 
 extern struct vfsmount *proc_mnt;
-extern int proc_fill_super(struct super_block *,void *,int);
+struct pid_namespace;
+extern int proc_fill_super(struct super_block *, struct pid_namespace *);
 extern struct inode *proc_get_inode(struct super_block *, unsigned int, struct proc_dir_entry *);
 
 /*
@@ -143,6 +144,9 @@ extern const struct file_operations proc
 extern const struct file_operations proc_kmsg_operations;
 extern const struct file_operations ppc_htab_operations;
 
+extern int pid_ns_prepare_proc(struct pid_namespace *ns);
+extern void pid_ns_release_proc(struct pid_namespace *ns);
+
 /*
  * proc_tty.c
  */
@@ -248,6 +254,15 @@ static inline void proc_tty_unregister_d
 
 extern struct proc_dir_entry proc_root;
 
+static inline int pid_ns_prepare_proc(struct pid_namespace *ns)
+{
+	return 0;
+}
+
+static inline void pid_ns_release_proc(struct pid_namespace *ns)
+{
+}
+
 #endif /* CONFIG_PROC_FS */
 
 #if !defined(CONFIG_PROC_KCORE)