2 files changed, 103 insertions, 0 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index d352fb4b7709..27bf203ef05a 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -7583,6 +7583,91 @@ static const struct file_operations snapshot_raw_fops = {
 
 #endif /* CONFIG_TRACER_SNAPSHOT */
 
+/*
+ * trace_min_max_write - Write a u64 value to a trace_min_max_param struct
+ * @filp: The active open file structure
+ * @ubuf: The userspace provided buffer to read value into
+ * @cnt: The maximum number of bytes to read
+ * @ppos: The current "file" position
+ *
+ * This function implements the write interface for a struct trace_min_max_param.
+ * The filp->private_data must point to a trace_min_max_param structure that
+ * defines where to write the value, the min and the max acceptable values,
+ * and a lock to protect the write.
+ */
+static ssize_t
+trace_min_max_write(struct file *filp, const char __user *ubuf, size_t cnt, loff_t *ppos)
+{
+	struct trace_min_max_param *param = filp->private_data;
+	u64 val;
+	int err;
+
+	if (!param)
+		return -EFAULT;
+
+	err = kstrtoull_from_user(ubuf, cnt, 10, &val);
+	if (err)
+		return err;
+
+	if (param->lock)
+		mutex_lock(param->lock);
+
+	if (param->min && val < *param->min)
+		err = -EINVAL;
+
+	if (param->max && val > *param->max)
+		err = -EINVAL;
+
+	if (!err)
+		*param->val = val;
+
+	if (param->lock)
+		mutex_unlock(param->lock);
+
+	if (err)
+		return err;
+
+	return cnt;
+}
+
+/*
+ * trace_min_max_read - Read a u64 value from a trace_min_max_param struct
+ * @filp: The active open file structure
+ * @ubuf: The userspace provided buffer to read value into
+ * @cnt: The maximum number of bytes to read
+ * @ppos: The current "file" position
+ *
+ * This function implements the read interface for a struct trace_min_max_param.
+ * The filp->private_data must point to a trace_min_max_param struct with valid
+ * data.
+ */
+static ssize_t
+trace_min_max_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
+{
+	struct trace_min_max_param *param = filp->private_data;
+	char buf[U64_STR_SIZE];
+	int len;
+	u64 val;
+
+	if (!param)
+		return -EFAULT;
+
+	val = *param->val;
+
+	if (cnt > sizeof(buf))
+		cnt = sizeof(buf);
+
+	len = snprintf(buf, sizeof(buf), "%llu\n", val);
+
+	return simple_read_from_buffer(ubuf, cnt, ppos, buf, len);
+}
+
+const struct file_operations trace_min_max_fops = {
+	.open		= tracing_open_generic,
+	.read		= trace_min_max_read,
+	.write		= trace_min_max_write,
+};
+
 #define TRACING_LOG_ERRS_MAX	8
 #define TRACING_LOG_LOC_MAX	128
 
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index cd80d046c7a5..22f8c652ef8b 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1952,4 +1952,22 @@ static inline bool is_good_name(const char *name)
 	return true;
 }
 
+/*
+ * This is a generic way to read and write a u64 value from a file in tracefs.
+ *
+ * The value is stored on the variable pointed by *val. The value needs
+ * to be at least *min and at most *max. The write is protected by an
+ * existing *lock.
+ */
+struct trace_min_max_param {
+	struct mutex	*lock;
+	u64		*val;
+	u64		*min;
+	u64		*max;
+};
+
+#define U64_STR_SIZE		24	/* 20 digits max */
+
+extern const struct file_operations trace_min_max_fops;
+
 #endif /* _LINUX_KERNEL_TRACE_H */