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authorEric W. Biederman <ebiederm@xmission.com>2012-01-30 21:23:52 -0800
committerEric W. Biederman <ebiederm@xmission.com>2012-02-01 19:20:57 -0800
commit60f126d93b210ae708e2a5bb4a3be2121831f2a0 (patch)
tree1ebdf75d1a8bca0122b6dcb34a7efae2a1839919 /fs/proc/proc_sysctl.c
parent0eb97f38d2bfaea289b44c5140a7b04e7b369bad (diff)
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>
Diffstat (limited to 'fs/proc/proc_sysctl.c')
-rw-r--r--fs/proc/proc_sysctl.c16
1 files changed, 16 insertions, 0 deletions
diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 722ec116208..e5601dc2408 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);