Because I plan to use RasPi as a media center, I chose Raspbmc as the operating system. It's based on Raspbian, which is basically Debian on ARM with some Raspberry specific packages. I'm sure I can get anything on this.
Then came the problems. Gphoto can control DSLRs and after initial problems, I got it working with my EOS 1100D. On RasPi, however, there are some more problems. First run works properly, but after the first I get only:
*** Error ***
PTP I/O error
*** Error ***
An error occurred in the io-library ('Unspecified error'): No error description available
After googling a bit and asking on #gphoto at Freenode, I found out the problem is not with Gphoto, but with Raspberry Pi. Hardware or software, no one seems to know.
There is a workaround!
After taking a photo with
gphoto2 --wait-event=2s --set-config eosremoterelease=Immediate --wait-event=180s --set-config eosremoterelease=Off --wait-event-and-download=5s
the usb connection has to be reset. I found a piece of code to do just that: http://marc.info/?l=linux-usb&m=121459435621262&w=2. I copypasted that into usbreset.c, compiled it with gcc usbreset.c -o usbreset, and now taking photos seems to work. I'm running a loop of taking a photo, resetting usb and deleting the photos. While I'm writing this, it has successfully taken over 50 photos in a row.
Next I'm going to write a script to take photos, renaming them and sending them directly to my NAS.