[arch-general] Finally found a solution to slow USB on HAL

[Dave Reisner]

On Mon, Jun 28, 2010 at 07:09:11PM -0300, Denis A. Altoé Falqueto wrote:
> On Mon, Jun 28, 2010 at 5:52 PM, Philipp Überbacher
> <hollunder at lavabit.com> wrote:
> > Actually I was recently wondering a bit about the unmounting part,
> > especially with USB sticks. I do have udev rules, taken from the wiki,
> > in place that handle automatic mounting. There's also a unmounting part,
> > which afair removes created dirs, but I guess this is only called after
> > the usb drive is removed. It did happen more than once to me that a file
> > transfer seemed to be complete, but when I just removed the drive, the
> > data was gone. Is there a way to provide automatic safe removal? Manual
> > unmounting is a bit of a PITA, as you need to have a terminal ready,
> > guess sdN and type a line, where the device guessing part is the most
> > problematic. I tend to use /dev/sdN to make sure that I remove the
> > device from all mount points. Thanks for any advice.
> 
> Well, automounting is really easy, but auto-unmounting (!?) is
> complex, because what triggers the event is the removal of the device,
> but after you take it, the S.O. can't do anything about it anymore. I
> use KDE, so I can mount and unmount easily. Gnome and XFCE also offer
> good services for that. But without those, I fear that you'll need to
> issue unmount manually.
> 
Not entirely true. You can assign the results of a blkid call to the
sysfs node that correlates to the flash drive. A snip from my mounted
flash drive..

...
E: SUBSYSTEM=block
E: DEVNAME=sde1
E: ID_FS_LABEL=Flashy
E: ID_FS_LABEL_ENC=Flashy
E: ID_FS_UUID=6E1B5F1E742ED9F4
E: ID_FS_UUID_ENC=6E1B5F1E742ED9F4
E: ID_FS_TYPE=ntfs
E: ID_FS_USAGE=filesystem
...

The ID_FS_xxxx info is from blkid. On the REMOVE event, this information
is still accessible, so I know where the drive is mounted because I
always mount by label. When I remove the drive (without calling umount),
the mount point is destroyed as well.

Ensure that you're mounting the flash drive with 'sync' if you want to
be able to remove it without calling umount. This will slow down
transfers, but data is written synchronously to disk rather than to an
intermediate buffer.

As always, the Arch Wiki has examples of this on the Udev page.

/dave