Bill Nottingham wrote:
Hans de Goede (j.w.r.degoede@xxxxxx) said:
I'm basing my work on the i2c-tools specfile from Suse (one of the
lm_sensors project lead works for Suse).
This specfile contains in %files:
%attr(660, root, root) %dev(c, 89, 0) /lib/udev/devices/i2c-0
This causes a /dev/i2c-0 char device to be effectively statically created.
If I then also add the proper alias to modprobe.conf.dist, tools like
i2cdump which need the i2c-dev kernel module loaded will automagically
work.
Is this ok / the best way todo this. Also I will be adding i2c-0 to i2c-3
then, as there are many cases where there is more then 1 i2c bus (some
motherboards have 2 on the board and many graphics / tv cards have i2c
busses).
What are the modules that live behind that device?
The module / driver behind it us i2c-dev, which gives userspace access to one
ore more i2c-busses. So the chain basically is:
-userspace app (i2cdump for example) -> i2c-dev -> i2c master driver (i2c-i801
for example).
Notice that under normal circumstances userspace access to the i2c busses is
not used, its main use is as a debugging / development technique.
I just thought the same problem exists for non hardware backed devices like
loop. Then I noticed that loop.ko is loaded, removing it and then trying a
mount -o loop will cause mount to fail because it cannot find /dev/loop#.
Who / what is responsible for loop.ko getting loaded by default, wouldn't
it be better to use a similar trick with a static /dev entry and module
autoloading, this would probably save both boottime and memory.
loop is created by /etc/udev/makedev.d/50-udev.nodes.
Hmm,
Interesting this seems to be different from adding entries under
/lib/udev/devices, as as said on my system after dev the loop module gets
loaded, while I assume its not used during boot. Wouldn't it be better (faster,
less memory use) for the loop-devices to sit under /lib/udev/devices, so that
no module gets loaded?
Regards,
Hans
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