tracing: Keep track of set_ftrace_filter position and allow lseek again

This patch keeps track of the index within the elements of
set_ftrace_filter and if the position goes backwards, it nicely
resets and starts from the beginning again.

This allows for lseek and pread to work properly now.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 26 insertions, 8 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index c8db0dbb984e..2d51166b93fe 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1368,6 +1368,7 @@ enum {
 #define FTRACE_BUFF_MAX (KSYM_SYMBOL_LEN+4) /* room for wildcards */
 
 struct ftrace_iterator {
+        loff_t                          pos;
         loff_t                          func_pos;
         struct ftrace_page              *pg;
         struct dyn_ftrace               *func;
@@ -1385,9 +1386,8 @@ t_hash_next(struct seq_file *m, loff_t *pos)
         struct hlist_node *hnd = NULL;
         struct hlist_head *hhd;
 
-        WARN_ON(!(iter->flags & FTRACE_ITER_HASH));
-
         (*pos)++;
+        iter->pos = *pos;
 
         if (iter->probe)
                 hnd = &iter->probe->node;
@@ -1427,14 +1427,9 @@ static void *t_hash_start(struct seq_file *m, loff_t *pos)
         void *p = NULL;
         loff_t l;
 
-        if (!(iter->flags & FTRACE_ITER_HASH))
-                iter->func_pos = *pos;
-
         if (iter->func_pos > *pos)
                 return NULL;
 
-        iter->flags |= FTRACE_ITER_HASH;
-
         iter->hidx = 0;
         for (l = 0; l <= (*pos - iter->func_pos); ) {
                 p = t_hash_next(m, &l);
@@ -1444,6 +1439,9 @@ static void *t_hash_start(struct seq_file *m, loff_t *pos)
         if (!p)
                 return NULL;
 
+        /* Only set this if we have an item */
+        iter->flags |= FTRACE_ITER_HASH;
+
         return iter;
 }
 
@@ -1478,6 +1476,8 @@ t_next(struct seq_file *m, void *v, loff_t *pos)
                 return t_hash_next(m, pos);
 
         (*pos)++;
+        iter->pos = *pos;
+        iter->func_pos = *pos;
 
         if (iter->flags & FTRACE_ITER_PRINTALL)
                 return NULL;
@@ -1517,6 +1517,13 @@ t_next(struct seq_file *m, void *v, loff_t *pos)
         return iter;
 }
 
+static void reset_iter_read(struct ftrace_iterator *iter)
+{
+        iter->pos = 0;
+        iter->func_pos = 0;
+        iter->flags &= ~(FTRACE_ITER_PRINTALL & FTRACE_ITER_HASH);
+}
+
 static void *t_start(struct seq_file *m, loff_t *pos)
 {
         struct ftrace_iterator *iter = m->private;
@@ -1525,6 +1532,12 @@ static void *t_start(struct seq_file *m, loff_t *pos)
 
         mutex_lock(&ftrace_lock);
         /*
+         * If an lseek was done, then reset and start from beginning.
+         */
+        if (*pos < iter->pos)
+                reset_iter_read(iter);
+
+        /*
          * For set_ftrace_filter reading, if we have the filter
          * off, we can short cut and just print out that all
          * functions are enabled.
@@ -1541,6 +1554,11 @@ static void *t_start(struct seq_file *m, loff_t *pos)
         if (iter->flags & FTRACE_ITER_HASH)
                 return t_hash_start(m, pos);
 
+        /*
+         * Unfortunately, we need to restart at ftrace_pages_start
+         * every time we let go of the ftrace_mutex. This is because
+         * those pointers can change without the lock.
+         */
         iter->pg = ftrace_pages_start;
         iter->idx = 0;
         for (l = 0; l <= *pos; ) {
@@ -2447,7 +2465,7 @@ static const struct file_operations ftrace_filter_fops = {
         .open = ftrace_filter_open,
         .read = seq_read,
         .write = ftrace_filter_write,
-        .llseek = no_llseek,
+        .llseek = ftrace_regex_lseek,
         .release = ftrace_filter_release,
 };