On Tue, Aug 29, 2006 at 08:30:45AM -0700, David Brownell wrote:
> On Monday 28 August 2006 1:27 pm, Sam Bishop wrote:
> > + /* To see what's changed, compare the file's previous and current
> > + contents or scan the filesystem. (Scanning is more precise.) */
>
> Rather than "more precise", "less error prone" ... there are nasty error
> paths in the "compare" case. Better yet, don't mention that.
Sure. I also removed the bit where I call HAL a program...
Thanks for your help, David.
A little more detail on how and when to poll() /proc/bus/usb/devices.
Signed-off-by: Sam Bishop <[EMAIL PROTECTED]>
--- linux-2.6.17.9/Documentation/DocBook/usb.tmpl.orig 2006-08-24
13:32:07.602622546 -0600
+++ linux-2.6.17.9/Documentation/DocBook/usb.tmpl 2006-08-29
10:25:25.913847688 -0600
@@ -463,14 +463,25 @@
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>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. */
+}</programlisting>
+ Note that this behavior is intended to be used for informational
+ and debug purposes. It would be more appropriate to use udev or
+ HAL to initialize a device or start a user-mode helper program, for
+ instance.
</para>
-
</sect1>
<sect1>
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