[PATCH] sysctl: factor out sysctl_head_next from do_sysctl

The current logic to walk through the list of sysctl table headers is slightly
painful and implement in a way it cannot be used by code outside sysctl.c

I am in the process of implementing a version of the sysctl proc support that
instead of using the proc generic non-caching monster, just uses the existing
sysctl data structure as backing store for building the dcache entries and for
doing directory reads.  To use the existing data structures however I need a
way to get at them.

[akpm@osdl.org: warning fix]
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 47 insertions, 17 deletions

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 396b8d984c5d..72ba58b362d8 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -924,6 +924,10 @@ enum
 #ifdef __KERNEL__
 #include <linux/list.h>
 
+/* For the /proc/sys support */
+extern struct ctl_table_header *sysctl_head_next(struct ctl_table_header *prev);
+extern void sysctl_head_finish(struct ctl_table_header *prev);
+
 extern void sysctl_init(void);
 
 typedef struct ctl_table ctl_table;
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 6ccb6cc19e28..c3e2ac9cb5fb 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1070,6 +1070,42 @@ static void start_unregistering(struct ctl_table_header *p)
         list_del_init(&p->ctl_entry);
 }
 
+void sysctl_head_finish(struct ctl_table_header *head)
+{
+        if (!head)
+                return;
+        spin_lock(&sysctl_lock);
+        unuse_table(head);
+        spin_unlock(&sysctl_lock);
+}
+
+struct ctl_table_header *sysctl_head_next(struct ctl_table_header *prev)
+{
+        struct ctl_table_header *head;
+        struct list_head *tmp;
+        spin_lock(&sysctl_lock);
+        if (prev) {
+                tmp = &prev->ctl_entry;
+                unuse_table(prev);
+                goto next;
+        }
+        tmp = &root_table_header.ctl_entry;
+        for (;;) {
+                head = list_entry(tmp, struct ctl_table_header, ctl_entry);
+
+                if (!use_table(head))
+                        goto next;
+                spin_unlock(&sysctl_lock);
+                return head;
+        next:
+                tmp = tmp->next;
+                if (tmp == &root_table_header.ctl_entry)
+                        break;
+        }
+        spin_unlock(&sysctl_lock);
+        return NULL;
+}
+
 void __init sysctl_init(void)
 {
 #ifdef CONFIG_PROC_SYSCTL
@@ -1081,7 +1117,7 @@ void __init sysctl_init(void)
 int do_sysctl(int __user *name, int nlen, void __user *oldval, size_t __user *oldlenp,
                void __user *newval, size_t newlen)
 {
-        struct list_head *tmp;
+        struct ctl_table_header *head;
         int error = -ENOTDIR;
 
         if (nlen <= 0 || nlen >= CTL_MAXNAME)
@@ -1091,26 +1127,16 @@ int do_sysctl(int __user *name, int nlen, void __user *oldval, size_t __user *ol
                 if (!oldlenp || get_user(old_len, oldlenp))
                         return -EFAULT;
         }
-        spin_lock(&sysctl_lock);
-        tmp = &root_table_header.ctl_entry;
-        do {
-                struct ctl_table_header *head =
-                        list_entry(tmp, struct ctl_table_header, ctl_entry);
-
-                if (!use_table(head))
-                        continue;
-
-                spin_unlock(&sysctl_lock);
 
+        for (head = sysctl_head_next(NULL); head;
+                        head = sysctl_head_next(head)) {
                 error = parse_table(name, nlen, oldval, oldlenp, 
                                         newval, newlen, head->ctl_table);
-
-                spin_lock(&sysctl_lock);
-                unuse_table(head);
-                if (error != -ENOTDIR)
+                if (error != -ENOTDIR) {
+                        sysctl_head_finish(head);
                         break;
-        } while ((tmp = tmp->next) != &root_table_header.ctl_entry);
-        spin_unlock(&sysctl_lock);
+                }
+        }
         return error;
 }