sysctl: Rewrite proc_sys_readdir in terms of first_entry and next_entry

Replace sysctl_head_next with first_entry and next_entry.  These new
iterators operate at the level of sysctl table entries and filter
out any sysctl tables that should not be shown.

Utilizing two specialized functions instead of a single function removes
conditionals for handling awkward special cases that only come up
at the beginning of iteration, making the iterators easier to read
and understand.

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

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 3b63f298ce288486a47247138dfe915202a58edb..d9c3ae6afe4c78bf1886fbeb371ca3d35098e950 100644 (file)
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -243,31 +243,25 @@ static struct ctl_table *lookup_entry(struct ctl_table_header **phead,
        return entry;
 }
 
-static struct ctl_table_header *__sysctl_head_next(struct nsproxy *namespaces,
-                                               struct ctl_table_header *prev)
+static struct ctl_table_header *next_usable_entry(struct ctl_table *dir,
+       struct ctl_table_root *root, struct list_head *tmp)
 {
-       struct ctl_table_root *root;
+       struct nsproxy *namespaces = current->nsproxy;
        struct list_head *header_list;
        struct ctl_table_header *head;
-       struct list_head *tmp;
 
-       spin_lock(&sysctl_lock);
-       if (prev) {
-               head = prev;
-               tmp = &prev->ctl_entry;
-               unuse_table(prev);
-               goto next;
-       }
-       tmp = &root_table_header.ctl_entry;
+       goto next;
        for (;;) {
                head = list_entry(tmp, struct ctl_table_header, ctl_entry);
+               root = head->root;
 
-               if (!use_table(head))
+               if (head->attached_to != dir ||
+                   !head->attached_by->procname ||
+                   !use_table(head))
                        goto next;
-               spin_unlock(&sysctl_lock);
+
                return head;
        next:
-               root = head->root;
                tmp = tmp->next;
                header_list = lookup_header_list(root, namespaces);
                if (tmp != header_list)
@@ -283,13 +277,53 @@ static struct ctl_table_header *__sysctl_head_next(struct nsproxy *namespaces,
                tmp = header_list->next;
        }
 out:
-       spin_unlock(&sysctl_lock);
        return NULL;
 }
 
-static struct ctl_table_header *sysctl_head_next(struct ctl_table_header *prev)
+static void first_entry(
+       struct ctl_table_header *dir_head, struct ctl_table *dir,
+       struct ctl_table_header **phead, struct ctl_table **pentry)
 {
-       return __sysctl_head_next(current->nsproxy, prev);
+       struct ctl_table_header *head = dir_head;
+       struct ctl_table *entry = dir;
+
+       spin_lock(&sysctl_lock);
+       if (entry->procname) {
+               use_table(head);
+       } else {
+               head = next_usable_entry(dir, &sysctl_table_root,
+                                        &sysctl_table_root.default_set.list);
+               if (head)
+                       entry = head->attached_by;
+       }
+       spin_unlock(&sysctl_lock);
+       *phead = head;
+       *pentry = entry;
+}
+
+static void next_entry(struct ctl_table *dir,
+       struct ctl_table_header **phead, struct ctl_table **pentry)
+{
+       struct ctl_table_header *head = *phead;
+       struct ctl_table *entry = *pentry;
+
+       entry++;
+       if (!entry->procname) {
+               struct ctl_table_root *root = head->root;
+               struct list_head *tmp = &head->ctl_entry;
+               if (head->attached_to != dir) {
+                       root = &sysctl_table_root;
+                       tmp = &sysctl_table_root.default_set.list;
+               }
+               spin_lock(&sysctl_lock);
+               unuse_table(head);
+               head = next_usable_entry(dir, root, tmp);
+               spin_unlock(&sysctl_lock);
+               if (head)
+                       entry = head->attached_by;
+       }
+       *phead = head;
+       *pentry = entry;
 }
 
 void register_sysctl_root(struct ctl_table_root *root)
@@ -533,20 +567,17 @@ static int scan(struct ctl_table_header *head, ctl_table *table,
                unsigned long *pos, struct file *file,
                void *dirent, filldir_t filldir)
 {
+       int res;
 
-       for (; table->procname; table++, (*pos)++) {
-               int res;
+       if ((*pos)++ < file->f_pos)
+               return 0;
 
-               if (*pos < file->f_pos)
-                       continue;
+       res = proc_sys_fill_cache(file, dirent, filldir, head, table);
 
-               res = proc_sys_fill_cache(file, dirent, filldir, head, table);
-               if (res)
-                       return res;
+       if (res == 0)
+               file->f_pos = *pos;
 
-               file->f_pos = *pos + 1;
-       }
-       return 0;
+       return res;
 }
 
 static int proc_sys_readdir(struct file *filp, void *dirent, filldir_t filldir)
@@ -556,6 +587,7 @@ static int proc_sys_readdir(struct file *filp, void *dirent, filldir_t filldir)
        struct ctl_table_header *head = grab_header(inode);
        struct ctl_table *table = PROC_I(inode)->sysctl_entry;
        struct ctl_table_header *h = NULL;
+       struct ctl_table *entry;
        unsigned long pos;
        int ret = -EINVAL;
 
@@ -585,14 +617,8 @@ static int proc_sys_readdir(struct file *filp, void *dirent, filldir_t filldir)
        }
        pos = 2;
 
-       ret = scan(head, table, &pos, filp, dirent, filldir);
-       if (ret)
-               goto out;
-
-       for (h = sysctl_head_next(NULL); h; h = sysctl_head_next(h)) {
-               if (h->attached_to != table)
-                       continue;
-               ret = scan(h, h->attached_by, &pos, filp, dirent, filldir);
+       for (first_entry(head, table, &h, &entry); h; next_entry(table, &h, &entry)) {
+               ret = scan(h, entry, &pos, filp, dirent, filldir);
                if (ret) {
                        sysctl_head_finish(h);
                        break;