title: Max number of bytes available for sysfs read
body: <p>To handle a <code>sysfs</code> read I need to create a <code>show</code> function which is added to a <code>kobj_attribute</code> structure. The prototype of <a href="https://elixir.bootlin.com/linux/v4.14.63/source/include/linux/kobject.h#L145" rel="nofollow noreferrer">the function is defined as</a>:</p>
  
  <pre><code>ssize_t (*show)(struct kobject *kobj, struct kobj_attribute *attr,
              char *buf);
  </code></pre>
  
  <p>Obviously I need to write data to the <code>buf</code> parameter, but what is the upper limit of the number of bytes which can be written? Is it defined anywhere?</p>