+ssize_t simple_read_from_buffer(void __user *to, size_t count, loff_t *ppos,
+ const void *from, size_t available)
+{
+ loff_t pos = *ppos;
+ if (pos < 0)
+ return -EINVAL;
+ if (pos >= available)
+ return 0;
+ if (count > available - pos)
+ count = available - pos;
+ if (copy_to_user(to, from + pos, count))
+ return -EFAULT;
+ *ppos = pos + count;
+ return count;
+}
+
+/*
+ * Transaction based IO.
+ * The file expects a single write which triggers the transaction, and then
+ * possibly a read which collects the result - which is stored in a
+ * file-local buffer.
+ */
+char *simple_transaction_get(struct file *file, const char __user *buf, size_t size)
+{
+ struct simple_transaction_argresp *ar;
+ static DEFINE_SPINLOCK(simple_transaction_lock);
+
+ if (size > SIMPLE_TRANSACTION_LIMIT - 1)
+ return ERR_PTR(-EFBIG);
+
+ ar = (struct simple_transaction_argresp *)get_zeroed_page(GFP_KERNEL);
+ if (!ar)
+ return ERR_PTR(-ENOMEM);
+
+ spin_lock(&simple_transaction_lock);
+
+ /* only one write allowed per open */
+ if (file->private_data) {
+ spin_unlock(&simple_transaction_lock);
+ free_page((unsigned long)ar);
+ return ERR_PTR(-EBUSY);
+ }
+
+ file->private_data = ar;
+
+ spin_unlock(&simple_transaction_lock);
+
+ if (copy_from_user(ar->data, buf, size))
+ return ERR_PTR(-EFAULT);
+
+ return ar->data;
+}
+
+ssize_t simple_transaction_read(struct file *file, char __user *buf, size_t size, loff_t *pos)
+{
+ struct simple_transaction_argresp *ar = file->private_data;
+
+ if (!ar)
+ return 0;
+ return simple_read_from_buffer(buf, size, pos, ar->data, ar->size);
+}
+
+int simple_transaction_release(struct inode *inode, struct file *file)
+{
+ free_page((unsigned long)file->private_data);
+ return 0;
+}
+
+/* Simple attribute files */
+
+struct simple_attr {
+ u64 (*get)(void *);
+ void (*set)(void *, u64);
+ char get_buf[24]; /* enough to store a u64 and "\n\0" */
+ char set_buf[24];
+ void *data;
+ const char *fmt; /* format for read operation */
+ struct mutex mutex; /* protects access to these buffers */
+};
+
+/* simple_attr_open is called by an actual attribute open file operation
+ * to set the attribute specific access operations. */
+int simple_attr_open(struct inode *inode, struct file *file,
+ u64 (*get)(void *), void (*set)(void *, u64),
+ const char *fmt)
+{
+ struct simple_attr *attr;
+
+ attr = kmalloc(sizeof(*attr), GFP_KERNEL);
+ if (!attr)
+ return -ENOMEM;
+
+ attr->get = get;
+ attr->set = set;
+ attr->data = inode->i_private;
+ attr->fmt = fmt;
+ mutex_init(&attr->mutex);
+
+ file->private_data = attr;
+
+ return nonseekable_open(inode, file);
+}
+
+int simple_attr_close(struct inode *inode, struct file *file)
+{
+ kfree(file->private_data);
+ return 0;
+}
+
+/* read from the buffer that is filled with the get function */
+ssize_t simple_attr_read(struct file *file, char __user *buf,
+ size_t len, loff_t *ppos)
+{
+ struct simple_attr *attr;
+ size_t size;
+ ssize_t ret;
+
+ attr = file->private_data;
+
+ if (!attr->get)
+ return -EACCES;
+
+ mutex_lock(&attr->mutex);
+ if (*ppos) /* continued read */
+ size = strlen(attr->get_buf);
+ else /* first read */
+ size = scnprintf(attr->get_buf, sizeof(attr->get_buf),
+ attr->fmt,
+ (unsigned long long)attr->get(attr->data));
+
+ ret = simple_read_from_buffer(buf, len, ppos, attr->get_buf, size);
+ mutex_unlock(&attr->mutex);
+ return ret;
+}
+
+/* interpret the buffer as a number to call the set function with */
+ssize_t simple_attr_write(struct file *file, const char __user *buf,
+ size_t len, loff_t *ppos)
+{
+ struct simple_attr *attr;
+ u64 val;
+ size_t size;
+ ssize_t ret;
+
+ attr = file->private_data;
+
+ if (!attr->set)
+ return -EACCES;
+
+ mutex_lock(&attr->mutex);
+ ret = -EFAULT;
+ size = min(sizeof(attr->set_buf) - 1, len);
+ if (copy_from_user(attr->set_buf, buf, size))
+ goto out;
+
+ ret = len; /* claim we got the whole input */
+ attr->set_buf[size] = '\0';
+ val = simple_strtol(attr->set_buf, NULL, 0);
+ attr->set(attr->data, val);
+out:
+ mutex_unlock(&attr->mutex);
+ return ret;
+}
+