[PATCH 1/2][RFC] containers: improve automatic container naming

["Serge E. Hallyn" <serue@us.ibm.com>]

This compiles and boots, but is not intended for inclusion in -mm (yet),
just as an RFC for the naming scheme to fix the bug Andrew pointed out.

Seem ok overall?

thanks,
-serge

>From 8e9b972f7482415777e982d3bc9a0d55cbaf862b Mon Sep 17 00:00:00 2001
From: Serge E. Hallyn <serue@us.ibm.com>
Date: Fri, 1 Jun 2007 15:32:15 -0400
Subject: [PATCH 1/2] containers: improve automatic container naming

The automatic naming of containers created using container_clone()
is currently broken (not protected from wraparound) and inconvenient.

Add a per-container counter for use in naming children of the container.
Before two unshares in a row by one process, and a third in another,
would result in

	/node1/node2
	/node3

The current scheme should result in

	/node1/node1
	/node2

Also, keep a hash table populated with used names, to protect
against counter wrap-around.

Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
---
 include/linux/container.h |    8 +++
 kernel/container.c        |  116 +++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 120 insertions(+), 4 deletions(-)

diff --git a/include/linux/container.h b/include/linux/container.h
index 37c0bdf..61c750d 100644
--- a/include/linux/container.h
+++ b/include/linux/container.h
@@ -75,6 +75,14 @@ struct container {
 	atomic_t count;
 
 	/*
+	 * these are to support automatic naming of automatically
+	 * created containers
+	 */
+	int auto_cnt_set;  /* 1 if thie container is using up a auto_cnt */
+	unsigned long auto_cnt; /* the auto_cnt it's using up */
+	unsigned long next_childcnt; /* next avail cnt for child containers */
+
+	/*
 	 * We link our 'sibling' struct into our parent's 'children'.
 	 * Our children link their 'sibling' into our 'children'.
 	 */
diff --git a/kernel/container.c b/kernel/container.c
index 6f80487..2b2f6f2 100644
--- a/kernel/container.c
+++ b/kernel/container.c
@@ -55,6 +55,7 @@
 #include <linux/time.h>
 #include <linux/backing-dev.h>
 #include <linux/sort.h>
+#include <linux/hash.h>
 
 #include <asm/uaccess.h>
 #include <asm/atomic.h>
@@ -1819,6 +1820,9 @@ static long container_create(struct container *parent, struct dentry *dentry,
 	INIT_LIST_HEAD(&cont->css_groups);
 	INIT_LIST_HEAD(&cont->release_list);
 
+	cont->auto_cnt_set = 0;
+	cont->next_childcnt = 0;
+
 	cont->parent = parent;
 	cont->root = parent->root;
 	cont->top_container = parent->top_container;
@@ -1894,6 +1898,71 @@ static inline int container_has_css_refs(struct container *cont)
 	return 0;
 }
 
+#define cnthash_shift 3
+#define childcnt_hash(ptr, nr) hash_long(nr+(unsigned long)ptr, cnthash_shift)
+static DEFINE_SPINLOCK(childcntlock);
+
+struct container_child_hash_elem {
+	struct container *parent;
+	unsigned long cnt;
+	struct hlist_node list;
+};
+
+static struct hlist_head cntnum_hash_list[1 << cnthash_shift];
+
+static void init_cntnum_hash(void)
+{
+	int i;
+
+	for (i=0; i<1 << cnthash_shift; i++)
+		INIT_HLIST_HEAD(&cntnum_hash_list[i]);
+}
+
+static inline struct container_child_hash_elem *find_cntnum_hash(
+		struct container *parent, unsigned long count)
+{
+	struct container_child_hash_elem *he;
+	struct hlist_head *h;
+	struct hlist_node *tmp;
+
+	h = &cntnum_hash_list[childcnt_hash(parent, count)];
+	hlist_for_each_entry(he, tmp, h, list) {
+		if (he->parent == parent && he->cnt == count)
+			return he;
+	}
+	return NULL;
+}
+
+#define UNSET_HASH 0
+#define SET_HASH 1
+static inline int set_cntnum_hash(struct container *parent,
+        unsigned long count, int set)
+{
+	struct container_child_hash_elem *he;
+	int idx;
+
+	he = find_cntnum_hash(parent, count);
+	if (he) {
+		if (!set) {
+			hlist_del(&he->list);
+			kfree(he);
+			return 0;
+		}
+		return -ENOENT;
+	}
+	if (!set)
+		return -ENOENT;
+	he = kmalloc(sizeof(*he), GFP_KERNEL);
+	if (!he)
+		return -ENOMEM;
+	he->parent = parent;
+	he->cnt = count;
+	INIT_HLIST_NODE(&he->list);
+	idx = childcnt_hash(parent, count);
+	hlist_add_head(&he->list, &cntnum_hash_list[idx]);
+	return 0;
+}
+
 static int container_rmdir(struct inode *unused_dir, struct dentry *dentry)
 {
 	struct container *cont = dentry->d_fsdata;
@@ -1941,6 +2010,15 @@ static int container_rmdir(struct inode *unused_dir, struct dentry *dentry)
 	dput(d);
 	root->number_of_containers--;
 
+	if (cont->auto_cnt_set) {
+		spin_lock(&childcntlock);
+		if (set_cntnum_hash(parent, cont->auto_cnt, UNSET_HASH))
+			printk(KERN_NOTICE "%s: could not unset %lu\n",
+				__FUNCTION__, cont->auto_cnt);
+		cont->auto_cnt_set = 0;
+		spin_unlock(&childcntlock);
+	}
+
 	if (!list_empty(&cont->release_list))
 		list_del(&cont->release_list);
 	set_bit(CONT_RELEASABLE, &parent->flags);
@@ -2063,6 +2141,8 @@ int __init container_init(void)
 	err = register_filesystem(&container_fs_type);
 	if (err < 0)
 		goto out;
+	
+	init_cntnum_hash();
 
 	entry = create_proc_entry("containers", 0, NULL);
 	if (entry)
@@ -2302,10 +2382,31 @@ void container_exit(struct task_struct *tsk, int run_callbacks)
 		put_css_group_taskexit(cg);
 }
 
-static atomic_t namecnt;
-static void get_unused_name(char *buf)
+/*
+ * the while (find_cntnum_hash) loop will only be hit after
+ * we wrap around on next_childnct, which should never happen.
+ */
+static int get_unused_name(struct container *parent, unsigned long *out_cnt,
+		char *buf)
 {
-	sprintf(buf, "node%d", atomic_inc_return(&namecnt));
+	unsigned long cnt;
+	int err = 0;
+
+	spin_lock(&childcntlock);
+	cnt = parent->next_childcnt;
+	while (find_cntnum_hash(parent, cnt))
+		cnt++;
+	err = set_cntnum_hash(parent, cnt, SET_HASH);
+	if (err)
+		goto out_unlock;
+
+	sprintf(buf, "node%lu", cnt);
+	parent->next_childcnt = cnt+1;
+	*out_cnt = cnt;
+
+out_unlock:
+	spin_unlock(&childcntlock);
+	return err;
 }
 
 /**
@@ -2318,6 +2419,7 @@ int container_clone(struct task_struct *tsk, struct container_subsys *subsys)
 	struct dentry *dentry;
 	int ret = 0;
 	char nodename[32];
+	unsigned long auto_cntnum;
 	struct container *parent, *child;
 	struct inode *inode;
 	struct css_group *cg;
@@ -2348,7 +2450,10 @@ int container_clone(struct task_struct *tsk, struct container_subsys *subsys)
 	mutex_unlock(&container_mutex);
 
 	/* Now do the VFS work to create a container */
-	get_unused_name(nodename);
+	ret = get_unused_name(parent, &auto_cntnum, nodename);
+	if (ret)
+		goto out_container_mutex;
+
 	inode = parent->dentry->d_inode;
 
 	/* Hold the parent directory mutex across this operation to
@@ -2380,6 +2485,8 @@ int container_clone(struct task_struct *tsk, struct container_subsys *subsys)
 		ret = -ENOMEM;
 		goto out_release;
 	}
+	child->auto_cnt_set = 1;
+	child->auto_cnt = auto_cntnum;
 
 	/* The container now exists. Retake container_mutex and check
 	 * that we're still in the same state that we thought we
@@ -2408,6 +2515,7 @@ int container_clone(struct task_struct *tsk, struct container_subsys *subsys)
  out_release:
 	mutex_unlock(&inode->i_mutex);
 
+ out_container_mutex:
 	mutex_lock(&container_mutex);
 	put_css_group(cg);
 	mutex_unlock(&container_mutex);
-- 
1.5.1.1.GIT