Thunar-volman and the deprecation of HAL in Xfce
Last week I started looking at thunar-volman (a program that performs certain actions when new devices are plugged in) with the goal to make it compatible with the latest release of thunar which uses GIO instead of ThunarVFS for almost everything that takes place under the hood.
Until now, volume management (monitoring and mounting) in Xfce was done through HAL, the hardware abstraction layer that is currently being deprecated and dropped by major distributions. The functionality previously provided by HAL has been moved into udev, udisks (formerly known as DeviceKit-disks) and upower (formerly known as DeviceKit-power).
Volume management is transparently supported by GIO, meaning that applications don’t have to worry about the backend implementation. It should, in theory, not matter whether HAL is used or udev/udisks. Unsurprisingly, in reality, things are not that trivial, mainly for two reasons:
- Due to its focus on file management, GIO only supports monitoring and detecting storage devices (DVD drives, USB sticks etc.). There is no way to be notified when e.g. a digital camera or a portable media player is plugged in. This is critical for the functionality of thunar-volman which until now supported everything from cameras, media players, blank CDs/DVDs, audio CDs, PDAs and printers to input devices like keyboards, mice and tablets.
- Mounting volumes with udisks seems to be somewhat incompatible with HAL. I tried to mount volumes with thunar-volman and exo-mount (both implemented on top of HAL) and was for the root password upon unmounting in Thunar (using GIO and gnome-disk-utility/DeviceKit-disks). It seems like volumes mounted with HAL are assumed to be mounted by a different than the current user and thus, require root privileges to be unmounted.
HAL being deprecated and somewhat incompatible with udisks, what are the consequences for Xfce, and for thunar and thunar-volman in particular?
Let us, for a moment, assume Xfce 4.8 and thunar 1.0 were released as they are today, with thunar using GIO (and udisks instead of HAL in all major Linux distributions) and the rest (like thunar-volman and exo-mount) depending on HAL. As mentioned before, exo-mount and thunar wouldn’t work together in multi-user setups. Thunar would no longer detect cameras, PDAs, audio CDs, blank disks, mice, keyboards, tablets, media players and thunar-volman would end up being completely useless, as it is not detecting devices by itself. I think it is safe to say that this is not what we want.
In the following, I will focus on how to deal with thunar-volman. The rest of Xfce faces a similar roadmap, however. With regards to thunar-volman, there are (at least) three sane options:
- Drop thunar-volman and only support auto-mounting storage devices from now on, directly implemented in thunar. What is very obvious about this solution is that a lot of possibly useful functionality is lost.
- Port thunar-volman to (g)udev/udisks/GIO and make it a standalone daemon so that thunar no longer has to spawn it when new devices are plugged in. The advantage of this approach is that thunar only needs to depend on GIO and doesn’t have to implement the device detection part.
- Port thunar-volman to (g)udev/udisks/GIO as described above and make thunar depend on (g)udev for device detection. Spawn thunar-volman when devices are added/removed. The advantage over the previous approach is that thunar-volman doesn’t have to run permanently as a daemon. The additional thunar dependency on (g)udev could be seen as a disadvantage but on the other hand, it basically replaces another (HAL).
Now, everyone knows that programmers are lazy people. So, in the hope of being able to save some work, I started a survey on the usage of thunar-volman. The idea was to find out which of its features are used most and whether there are some that nobody really cares about. Here are the results:
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Feature #Users Percentage
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Mount removable drives when hot-plugged 86 92.5%
Mount removable media when inserted 83 89.2%
Browse removable media when inserted 69 74.2%
Cameras: Import digital photographs when connected 31 33.3%
Play video CDs and DVDs when inserted 31 33.3%
Play audio CDs when inserted 30 32.3%
Burn a CD or DVD when a blank disc is inserted 21 22.6%
Portable Media Players: Play music files when connected 11 11.8%
Auto-run programs on new drives and media 7 7.5%
Automatically run a program when a printer is connected 7 7.5%
Auto-open files on new drives and media 6 6.5%
Sync Palm devices when connected 5 5.4%
Automatically run a program when an USB keyboard is connected 3 3.2%
Automatically run a program when an USB mouse is connected 3 3.2%
Automatically run a program when a tabled is connected 2 2.2%
Sync Pocket PC devices when connected 2 2.2%
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Thunar Volume Manager Usage Survey with 93 participants
According to the results of this survey, auto-mounting and browsing of removable drives and media have highest priority among the 93 participating thunar-volman users. This more or less covers the functionality we could cover with GIO alone (plus automatically running a program when new drives and media are inserted). However, a third of the users also use thunar-volman for importing photographs from digital cameras and for playing video and audio CDs as well as DVDs automatically. Almost a 25 percent of all users use thunar-volman to start their favorite burning software when a blank CD or DVD is inserted. Slightly more than 10 percent want thunar-volman to start playing music on portable media players when they are plugged in. Printers and Palms are also somewhat relevant.
This survey confirms my expectations that handling storage devices alone is not enough even though they clearly are the most important use case for thunar-volman. Our users seem to like the flexibility of thunar-volman and make use of it. This disqualifies option 1 and leaves us with options 2 and 3. I’m inclined to avoid another daemon and go for number 3.
In preparation for porting thunar and thunar-volman to udev/udisks/GIO, I’ve created a wiki page to collect information about how we can reliably distinguish the different device types based on udev properties: http://wiki.xfce.org/dev/thunar-volman-udev. If you have blue-ray disks, video CDs, a digital camera, a Pocket PC, a Palm, a USB printer or a graphics tablet, you could make me very happy if you inserted them or plugged them in and sent me the output of udevadm info --export-db to my Xfce email address together with a short hint what devices you’ve plugged in. Alternatively, you can paste/upload the output somewhere on the internet and comment on this blog post, and thereby help making future versions of Xfce better.
Cheers!