sysctl: Comments to make the code clearer.

Document get_subdir and that find_subdir alwasy takes a reference.

Suggested-by:  Lucian Adrian Grijincu <lucian.grijincu@gmail.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 722ec116208d..e5601dc24088 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -73,6 +73,7 @@ static int namecmp(const char *name1, int len1, const char *name2, int len2)
         return cmp;
 }
 
+/* Called under sysctl_lock */
 static struct ctl_table *find_entry(struct ctl_table_header **phead,
         struct ctl_dir *dir, const char *name, int namelen)
 {
@@ -864,6 +865,18 @@ static struct ctl_dir *new_dir(struct ctl_table_set *set,
         return new;
 }
 
+/**
+ * get_subdir - find or create a subdir with the specified name.
+ * @dir:  Directory to create the subdirectory in
+ * @name: The name of the subdirectory to find or create
+ * @namelen: The length of name
+ *
+ * Takes a directory with an elevated reference count so we know that
+ * if we drop the lock the directory will not go away.  Upon success
+ * the reference is moved from @dir to the returned subdirectory.
+ * Upon error an error code is returned and the reference on @dir is
+ * simply dropped.
+ */
 static struct ctl_dir *get_subdir(struct ctl_dir *dir,
                                   const char *name, int namelen)
 {
@@ -885,12 +898,14 @@ static struct ctl_dir *get_subdir(struct ctl_dir *dir,
         if (!new)
                 goto failed;
 
+        /* Was the subdir added while we dropped the lock? */
         subdir = find_subdir(dir, name, namelen);
         if (!IS_ERR(subdir))
                 goto found;
         if (PTR_ERR(subdir) != -ENOENT)
                 goto failed;
 
+        /* Nope.  Use the our freshly made directory entry. */
         err = insert_header(dir, &new->header);
         subdir = ERR_PTR(err);
         if (err)
@@ -1190,6 +1205,7 @@ struct ctl_table_header *__register_sysctl_table(
 
         spin_lock(&sysctl_lock);
         dir = &set->dir;
+        /* Reference moved down the diretory tree get_subdir */
         dir->header.nreg++;
         spin_unlock(&sysctl_lock);