sysctl: Rewrite proc_sys_lookup introducing find_entry and lookup_entry.

Replace the helpers that proc_sys_lookup uses with helpers that work
in terms of an entire sysctl directory.  This is worse for sysctl_lock
hold times but it is much better for code clarity and the code cleanups
to come.

find_in_table is no longer needed so it is removed.

find_entry a general helper to find entries in a directory is added.

lookup_entry is a simple wrapper around find_entry that takes the
sysctl_lock increases the use count if an entry is found and drops
the sysctl_lock.

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

1 files changed, 76 insertions, 26 deletions

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 88d1b06cc5c0..3b63f298ce28 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -49,6 +49,55 @@ static struct ctl_table_root sysctl_table_root = {
 
 static DEFINE_SPINLOCK(sysctl_lock);
 
+static int namecmp(const char *name1, int len1, const char *name2, int len2)
+{
+        int minlen;
+        int cmp;
+
+        minlen = len1;
+        if (minlen > len2)
+                minlen = len2;
+
+        cmp = memcmp(name1, name2, minlen);
+        if (cmp == 0)
+                cmp = len1 - len2;
+        return cmp;
+}
+
+static struct ctl_table *find_entry(struct ctl_table_header **phead,
+        struct ctl_table_set *set,
+        struct ctl_table_header *dir_head, struct ctl_table *dir,
+        const char *name, int namelen)
+{
+        struct ctl_table_header *head;
+        struct ctl_table *entry;
+
+        if (dir_head->set == set) {
+                for (entry = dir; entry->procname; entry++) {
+                        const char *procname = entry->procname;
+                        if (namecmp(procname, strlen(procname), name, namelen) == 0) {
+                                *phead = dir_head;
+                                return entry;
+                        }
+                }
+        }
+
+        list_for_each_entry(head, &set->list, ctl_entry) {
+                if (head->unregistering)
+                        continue;
+                if (head->attached_to != dir)
+                        continue;
+                for (entry = head->attached_by; entry->procname; entry++) {
+                        const char *procname = entry->procname;
+                        if (namecmp(procname, strlen(procname), name, namelen) == 0) {
+                                *phead = head;
+                                return entry;
+                        }
+                }
+        }
+        return NULL;
+}
+
 static void init_header(struct ctl_table_header *head,
         struct ctl_table_root *root, struct ctl_table_set *set,
         struct ctl_table *table)
@@ -168,6 +217,32 @@ lookup_header_list(struct ctl_table_root *root, struct nsproxy *namespaces)
         return &set->list;
 }
 
+static struct ctl_table *lookup_entry(struct ctl_table_header **phead,
+                                      struct ctl_table_header *dir_head,
+                                      struct ctl_table *dir,
+                                      const char *name, int namelen)
+{
+        struct ctl_table_header *head;
+        struct ctl_table *entry;
+        struct ctl_table_root *root;
+        struct ctl_table_set *set;
+
+        spin_lock(&sysctl_lock);
+        root = &sysctl_table_root;
+        do {
+                set = lookup_header_set(root, current->nsproxy);
+                entry = find_entry(&head, set, dir_head, dir, name, namelen);
+                if (entry && use_table(head))
+                        *phead = head;
+                else
+                        entry = NULL;
+                root = list_entry(root->root_list.next,
+                                  struct ctl_table_root, root_list);
+        } while (!entry && root != &sysctl_table_root);
+        spin_unlock(&sysctl_lock);
+        return entry;
+}
+
 static struct ctl_table_header *__sysctl_head_next(struct nsproxy *namespaces,
                                                 struct ctl_table_header *prev)
 {
@@ -284,21 +359,6 @@ out:
         return inode;
 }
 
-static struct ctl_table *find_in_table(struct ctl_table *p, struct qstr *name)
-{
-        for ( ; p->procname; p++) {
-                if (strlen(p->procname) != name->len)
-                        continue;
-
-                if (memcmp(p->procname, name->name, name->len) != 0)
-                        continue;
-
-                /* I have a match */
-                return p;
-        }
-        return NULL;
-}
-
 static struct ctl_table_header *grab_header(struct inode *inode)
 {
         struct ctl_table_header *head = PROC_I(inode)->sysctl;
@@ -328,17 +388,7 @@ static struct dentry *proc_sys_lookup(struct inode *dir, struct dentry *dentry,
 
         table = table ? table->child : &head->ctl_table[1];
 
-        p = find_in_table(table, name);
-        if (!p) {
-                for (h = sysctl_head_next(NULL); h; h = sysctl_head_next(h)) {
-                        if (h->attached_to != table)
-                                continue;
-                        p = find_in_table(h->attached_by, name);
-                        if (p)
-                                break;
-                }
-        }
-
+        p = lookup_entry(&h, head, table, name->name, name->len);
         if (!p)
                 goto out;