Today I have released uam-0.2. The new release adds a long-awaited feature — capability of mounting and unmounting ejectable media like CD and DVD disks. And it does so in a way much simpler than I expected.
But first, what is uam?
Unlike HAL (or udisks) it doesn’t introduce any additional daemons. It just installs a few udev rules and helper scripts. When a media device is added or removed, udev calls the scripts and they perform all the mount/umount operations as necessary. HAL/udisks not required anymore, neither do mounter daemons.
Isn’t that a very limited solution?
Of course uam can’t be as flexible as the HAL/udisks attempt. You can’t get it (easily) to do things like asking user for permission or password; well, it doesn’t even create mounted media icons on your desktop. But is that what you really want it to do?
You can tell uam is one of the plug & play apps. emerge uam, CR and newly-inserted media shall start appearing in
/media. There’s a config file too. If you want to fine-tune it a little, there are a few more switches and options in
/etc/udev/uam.conf. You can set mount options, mountpoint naming, device filtering…
But how does it handle CDs and DVDs without a daemon?
Before, it wasn’t possible to mount CDs without some kind of a polling daemon. HAL/udisks provided such a daemon; I was even considering adding such a daemon to uam. The other solution was to use
sys-apps/pmount which allows unprivileged users to mount removable media.
None of these is any longer necessary. Nowadays, kernel can poll ejectable drives itself and report media change (and eject) events through udev. As of 0.2, uam handles those events and is able to mount CDs as well.
In order to do that, the kernel polling has to be enabled. This can be done either per-device:
echo 5000 > /sys/block/sr0/events_poll_msecs
or by setting a common polling interval as
events_dfl_poll_msecs parameter to the
echo 5000 > /sys/module/block/parameters/events_dfl_poll_msecs
The interval is specified in milliseconds, i.e. the above examples set it to 5 seconds. Smaller intervals result in a quicker mounting of CDs, larger result in less polling overhead.