seq_file_sorted

Seq_file add support for sorted list

Add support for sorted list in seq_file. It aims at changing the way
/proc/modules and kallsyms iterates on the module list to remove a race between
module unload and module/symbol listing.

The list is sorted by ascending list_head pointer address.

Changelog:

When reading the data by small chunks (i.e. byte by byte), the index (ppos) is
incremented by seq_read() directly and no "next" callback is called when going
to the next module.

Therefore, use ppos instead of m->private to deal with the fact that this index
is incremented directly to pass to the next module in seq_read() after the
buffer has been emptied.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Al Viro <viro@zeniv.linux.org.uk>
CC: Rusty Russel <rusty@rustcorp.com.au>

1 files changed, 44 insertions, 0 deletions

diff --git a/fs/seq_file.c b/fs/seq_file.c
index 05d6b0e78c9..691c84baf4f 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -819,3 +819,47 @@ struct hlist_node *seq_hlist_next_rcu(void *v,
 		return rcu_dereference(node->next);
 }
 EXPORT_SYMBOL(seq_hlist_next_rcu);
+
+struct list_head *seq_sorted_list_start(struct list_head *head, loff_t *ppos)
+{
+	struct list_head *lh;
+
+	list_for_each(lh, head)
+		if ((unsigned long)lh >= *ppos) {
+			*ppos = (unsigned long)lh;
+			return lh;
+		}
+	return NULL;
+}
+EXPORT_SYMBOL(seq_sorted_list_start);
+
+struct list_head *seq_sorted_list_start_head(struct list_head *head,
+		loff_t *ppos)
+{
+	struct list_head *lh;
+
+	if (!*ppos) {
+		*ppos = (unsigned long)head;
+		return head;
+	}
+	list_for_each(lh, head)
+		if ((unsigned long)lh >= *ppos) {
+			*ppos = (long)lh->prev;
+			return lh->prev;
+		}
+	return NULL;
+}
+EXPORT_SYMBOL(seq_sorted_list_start_head);
+
+struct list_head *seq_sorted_list_next(void *p, struct list_head *head,
+		loff_t *ppos)
+{
+	struct list_head *lh;
+	void *next;
+
+	lh = ((struct list_head *)p)->next;
+	next = (lh == head) ? NULL : lh;
+	*ppos = next ? ((unsigned long)next) : (-1UL);
+	return next;
+}
+EXPORT_SYMBOL(seq_sorted_list_next);