sysctl: Initial support for auto-unregistering sysctl tables.

Add nreg to ctl_table_header.  When nreg drops to 0 the ctl_table_header
will be unregistered.

Factor out drop_sysctl_table from unregister_sysctl_table, and add
the logic for decrementing nreg.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 1544485..13faa48 100644 (file)
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -29,8 +29,9 @@ static struct ctl_table root_table[1];
 static struct ctl_table_root sysctl_table_root;
 static struct ctl_table_header root_table_header = {
        {{.count = 1,
-       .ctl_table = root_table,
-       .ctl_entry = LIST_HEAD_INIT(sysctl_table_root.default_set.list),}},
+         .nreg = 1,
+         .ctl_table = root_table,
+         .ctl_entry = LIST_HEAD_INIT(sysctl_table_root.default_set.list),}},
        .root = &sysctl_table_root,
        .set = &sysctl_table_root.default_set,
 };
@@ -938,6 +939,7 @@ struct ctl_table_header *__register_sysctl_table(
        header->unregistering = NULL;
        header->root = root;
        header->count = 1;
+       header->nreg = 1;
        if (sysctl_check_table(path, table))
                goto fail;
 
@@ -1192,6 +1194,20 @@ struct ctl_table_header *register_sysctl_table(struct ctl_table *table)
 }
 EXPORT_SYMBOL(register_sysctl_table);
 
+static void drop_sysctl_table(struct ctl_table_header *header)
+{
+       if (--header->nreg)
+               return;
+
+       start_unregistering(header);
+       if (!--header->parent->count) {
+               WARN_ON(1);
+               kfree_rcu(header->parent, rcu);
+       }
+       if (!--header->count)
+               kfree_rcu(header, rcu);
+}
+
 /**
  * unregister_sysctl_table - unregister a sysctl table hierarchy
  * @header: the header returned from register_sysctl_table
@@ -1224,13 +1240,7 @@ void unregister_sysctl_table(struct ctl_table_header * header)
        }
 
        spin_lock(&sysctl_lock);
-       start_unregistering(header);
-       if (!--header->parent->count) {
-               WARN_ON(1);
-               kfree_rcu(header->parent, rcu);
-       }
-       if (!--header->count)
-               kfree_rcu(header, rcu);
+       drop_sysctl_table(header);
        spin_unlock(&sysctl_lock);
 }
 EXPORT_SYMBOL(unregister_sysctl_table);

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 094bc5c..e40b8f6 100644 (file)
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -1032,6 +1032,7 @@ struct ctl_table_header
                        struct list_head ctl_entry;
                        int used;
                        int count;
+                       int nreg;
                };
                struct rcu_head rcu;
        };