[Devel] [PATCH 11/20] Make proc have multiple superblocks - one for each namespace

[xemul at openvz.org]

Each pid namespace have to be visible through its own proc mount. Thus
we need to have per-namespace proc trees with their own superblocks.

We cannot easily show different pid namespace via one global proc tree,
since each pid refers to different tasks in different namespaces. E.g.
pid 1 refers to the init task in the initial namespace and to some other
task when seeing from another namespace. Moreover - pid, exisintg in
one namespace may not exist in the other.

This approach has one move advantage is that the tasks from the init
namespace can see what tasks live in another namespace by reading
entries from another proc tree.

Signed-off-by: Pavel Emelyanov <xemul at openvz.org>
Cc: Oleg Nesterov <oleg at tv-sign.ru>

---

 fs/proc/inode.c               |    2 -
 fs/proc/root.c                |   67 +++++++++++++++++++++++++++++++++++++++---
 include/linux/pid_namespace.h |    3 +
 include/linux/proc_fs.h       |    3 +
 4 files changed, 69 insertions(+), 6 deletions(-)

--- ./fs/proc/inode.c.ve12	2007-08-06 14:54:42.000000000 +0400
+++ ./fs/proc/inode.c	2007-08-06 14:58:51.000000000 +0400
@@ -427,7 +428,7 @@ 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 inode * root_inode;
 
--- ./fs/proc/root.c.ve12	2007-08-06 14:54:42.000000000 +0400
+++ ./fs/proc/root.c	2007-08-06 14:58:51.000000000 +0400
@@ -18,32 +18,90 @@
 #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);
+		if (err) {
+			up_write(&sb->s_umount);
+			deactivate_super(sb);
+			return err;
+		}
+
+		ei = PROC_I(sb->s_root->d_inode);
+		if (!ei->pid) {
+			rcu_read_lock();
+			ei->pid = get_pid(find_pid_ns(1, ns));
+			rcu_read_unlock();
+		}
+
+		sb->s_flags |= MS_ACTIVE;
+		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);
+	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)
@@ -54,12 +112,13 @@ void __init proc_root_init(void)
 	err = register_filesystem(&proc_fs_type);
 	if (err)
 		return;
-	proc_mnt = kern_mount(&proc_fs_type);
+	proc_mnt = kern_mount_data(&proc_fs_type, &init_pid_ns);
 	err = PTR_ERR(proc_mnt);
 	if (IS_ERR(proc_mnt)) {
 		unregister_filesystem(&proc_fs_type);
 		return;
 	}
+
 	proc_misc_init();
 	proc_net = proc_mkdir("net", NULL);
 	proc_net_stat = proc_mkdir("net/stat", NULL);
--- ./include/linux/pid_namespace.h.ve12	2007-08-06 14:58:51.000000000 +0400
+++ ./include/linux/pid_namespace.h	2007-08-06 14:59:02.000000000 +0400
@@ -23,6 +23,9 @@ struct pid_namespace {
 	struct kmem_cache *pid_cachep;
 	int level;
 	struct pid_namespace *parent;
+#ifdef CONFIG_PROC_FS
+	struct vfsmount *proc_mnt;
+#endif
 };
 
 extern struct pid_namespace init_pid_ns;
--- ./include/linux/proc_fs.h.ve12	2007-08-06 14:58:51.000000000 +0400
+++ ./include/linux/proc_fs.h	2007-08-06 14:58:51.000000000 +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 *);
 extern struct inode *proc_get_inode(struct super_block *, unsigned int, struct proc_dir_entry *);
 
 /*