Linux driver access through sysfs
I'm making a small kernel module to provide user-space access to some kernel-mode only features of an ARMv7 chip (specifically, cache control). I'm reading through Linux Device Drivers by Corbet, Rubini, and Hartman. In it they describe how to make a full driver+device+bus. I don't want to create a bus driver at all. In fact the 'driver' that I'm making doesn't really need to match against a device definition at all - it is implicitly matched to the platform's CPU. Can anyone explain to me:
- Where in sysfs should my attributes go? Should it be in my module entry under
/sysfs/modules/mymodule
?/sys/devices/platform
seems promising too, and so does/sys/devices/system/cpu
. - If there is an existing place where I should put my
kobject开发者_如何转开发
/attributes, how do I plug it into it? How do I get the necessarykset
? All the examples I've seen create akset
and then link to it from thekobject
- I haven't seen an API for requesting an existing namedkset
?
Sorry if this is just impossibly obvious, or if there's some really straightforward and easily discovered example somewhere that I haven't discovered for some reason. Can anyone shed any light on this?
I haven't worked with sysfs much, but I found a simple-looking example that's pretty similar to what you are doing (naturally, it's also under ARM). Take a look at arch/arm/mach-omap1/pm.c
, specifically the idle_show
/idle_store
sysfs file. It gets registered (using sysfs_create_file()
) as /sys/power/sleep_while_idle
and uses the global /sys/power
kobj (defined in include/linux/kobject.h
). There are a few other global kobj's defined there that you could use, although I'm don't think any are a good fit for your driver.
Is this going to be a platform driver? As a driver that doesn't fit under any bus, it seems like a good fit. Platform drivers get their own directory under /sys/devices/platform, and can have attributes there. Take a look at drivers/hwmon/coretemp.c
, which has temp1_crit
, temp1_crit_alarm
, temp1_input
, etc. as attributes. It looks fairly simple: create the attributes (maybe with __ATTR()
?), list them all in an array, define an attribute_group
, register it with sysfs_create_group()
in the probe()
function, and unregister it with sysfs_remove_group()
in the remove()
function.
There are probably other platform drivers that define attributes (search for sysfs_create_group
) if you need other examples. Hope this helps!
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