USB doc patch 2
A little more detail on how and when to poll() /proc/bus/usb/devices.
Signed-off-by: Sam Bishop <sam@bishop.dhs.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/Documentation/DocBook/usb.tmpl b/Documentation/DocBook/usb.tmpl
index 8a28f76..3608472 100644
--- a/Documentation/DocBook/usb.tmpl
+++ b/Documentation/DocBook/usb.tmpl
@@ -453,14 +453,25 @@
file in your Linux kernel sources.
</para>
- <para>Otherwise the main use for this file from programs
- is to poll() it to get notifications of usb devices
- as they're plugged or unplugged.
- To see what changed, you'd need to read the file and
- compare "before" and "after" contents, scan the filesystem,
- or see its hotplug event.
- </para>
+ <para>This file, in combination with the poll() system call, can
+ also be used to detect when devices are added or removed:
+<programlisting>int fd;
+struct pollfd pfd;
+fd = open("/proc/bus/usb/devices", O_RDONLY);
+pfd = { fd, POLLIN, 0 };
+for (;;) {
+ /* The first time through, this call will return immediately. */
+ poll(&pfd, 1, -1);
+
+ /* To see what's changed, compare the file's previous and current
+ contents or scan the filesystem. (Scanning is more precise.) */
+}</programlisting>
+ Note that this behavior is intended to be used for informational
+ and debug purposes. It would be more appropriate to use programs
+ such as udev or HAL to initialize a device or start a user-mode
+ helper program, for instance.
+ </para>
</sect1>
<sect1>