[Buildroot] package/hotplug

Mitch Davis mjd+buildroot at afork.com
Wed Aug 25 05:35:13 UTC 2010


On Fri, Aug 20, 2010 at 4:59 AM, Michael S. Zick <minimod at morethan.org> wrote:
> On Thu August 19 2010, H Hartley Sweeten wrote:
>> On Thursday, August 19, 2010 10:58 AM, Will Newton wrote:
>> > On Thu, Aug 19, 2010 at 6:10 PM, H Hartley Sweeten wrote:
>> >> But, how to I get mdev to mount the drive after it's detected?
>> >
>> > it may be possible with the mdev config file. It seems to only be
>> > documented in the source:
>> >
>> > http://git.busybox.net/busybox/tree/util-linux/mdev.c
>> >
>> > See the section that mentions executing a command.
>> I figured it had something to do with the mdev.conf file.  I did
>> some grep'ing and found the KwikByte target handles this with a
>> custom '/sbin/automount.script' that is called by mdev.
>> I have modified my setup and it appears to be working.  When I plug
>> in the USB drive it is now detected and mounted.  The only issue I
>> have now is when the drive is removed.  mdev does call the script
>> to unmount the drive but I get two kernel errors:
>> usb 2-1.4: USB disconnect, address 4
>> FAT: bread failed in fat_clusters_flush
>> FAT: bread failed in fat_clusters_flush
>> I think these are generated because the drive is actually not present
>> when umount tries to unmount it.  I'm using the -f option (force unmount)
>> but that doesn't seem to prevent the error.
> It can't, the drive isn't there to write to once you remove it.
> Add a "safely unmount" thingy to whatever interface your device has,
> call a:
> mount -o remount device_name
> script.
> Note there is no option specified after the "remount" - not a typo here.
> That will make the kernel flush its VFS buffers for that device.

If you don't need to write to the device, you could also use "mount -o
ro" to make it read-only.  Then you won't get the message.  If it
happens that you need to write, you can temporarily call "mount -o
remount,rw", do your op, then "mount -o remount,ro".

Alternatively (and this is a little bit gross), if you don't want the
kernel to do any mounting, you may be able to hack "mtools" to use it
as a library:


Then the kernel wouldn't care if the device was pulled unexpectedly.


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