USB doc patch 2

	    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>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>