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@xxxxxxxxxxxxxxxx>
To: James Bruce <bruce@xxxxxxxxxxxxxx>
CC: linux-kernel@xxxxxxxxxxxxxxx, Casey Dahlin <cjdahlin@xxxxxxxx>
References: <fa.BwCgwGvTNIOD+KEeBrvP11xCEmw@xxxxxxxxxx>
<46CF6791.8040509@xxxxxxx> <46D00928.1080901@xxxxxxxxxxxxxx>
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,
Eric
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