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[Fwd: Re: USB Key light on/off state depending on mount]

I recently posted on lkml asking about making the light on your USB key shut off when it was not mounted. Some responses came back suggesting this is not difficult. Might we consider this for inclusion in Fedora?

-Casey Dahlin

-------- Original Message --------
Subject: 	Re: USB Key light on/off state depending on mount
Date: 	Sat, 25 Aug 2007 13:58:06 +0200
From: 	Éric Piel <Eric Piel tremplin-utc net>
To: 	James Bruce <bruce andrew cmu edu>
CC: 	linux-kernel vger kernel org, Casey Dahlin <cjdahlin ncsu edu>
References: <fa BwCgwGvTNIOD+KEeBrvP11xCEmw ifi uio no> <46CF6791 8040509 shaw ca> <46D00928 1080901 andrew cmu edu>

25/08/07 12:49, James Bruce wrote/a écrit:
Robert Hancock wrote:
Casey Dahlin wrote:
Most USB keys nowadays have a small LED somewhere inside of them that lights up when they are plugged in. On a windows box, the key is lit up whenever it is mounted, and as soon as it is unmounted it turns off, giving a handy physical indicator that the key is safe to remove. On linux, the light is simply on whenever the key is plugged in.

Should linux toggle the light depending on mount state? Is it as trivial as it seems or does this reflect some larger issue?

I think that Windows turns off power to the port when you do the "safely remove hardware" on it, or something like that. Mount/unmount doesn't really indicate whether the device is in use in Linux, though, since it can still be potentially accessed even when the device isn't mounted.

If there is a way to toggle the power state from userspace, then a desktop environment or userland tool can emulate the Windows behavior if that is desired. A lot of devices can charge via USB now, and this is actually more convenient on Linux than on Windows (in effect Windows requires drivers in order to charge something). However, having direct control over this is useful.
Yes, maybe some userspace such as HAL could turn off the usb devices at the same time it's unmounted. Actually that would be rather intuitive way to tell the user the umount is finished. There doesn't seem to be any loss of funcitonality, once it's turned off you can still re-access the device, and it's automatically turned on again (at least on my PC).

For the record, here is how one can switch off a usb device (as root):
# cd /sys/bus/usb/devices/usb*/[0-9]-[0-9] (just go to the directory of the device)
# echo -n 2 > *:1.0/power/state
# echo -n 2 > power/state

I use this to turn off my optical mouse when watching movies, but it works fine as well to turn off usb storage devices.
It can also be turned on with
# echo -n 0 > power/state

See you,
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