On 06/27/2017 05:23 AM, Sudip Mukherjee wrote:
On Mon, Jun 26, 2017 at 10:06:11AM -0700, Guenter Roeck wrote:
On Mon, Jun 26, 2017 at 03:33:20PM +0100, Sudip Mukherjee wrote:
Hi Guenter, Jean,
The patch d72d19c26c41 ("hwmon: (coretemp) Convert to use
devm_hwmon_device_register_with_groups") has changed the location of the
sysfs nodes from /sys/devices/platform/coretemp.0/ to
/sys/devices/platform/coretemp.0/hwmon/hwmon0/ and that has broken
some of our usespace applications when we have updated the kernel from
v3.8 to v4.4. For now I am reverting that said patch in our production
kernel (based on v4.4) but that is not an elegant solution.
Do you have any other reports like this? I am sure changing the paths
upstream will now break some other userspace. So, what can be an elegant
solution to our problem? or do we always need to carry an out-of-tree
patch for our production kernel?
The problem only occurs if attributes are accessed using the raw path,
and if user space does not take into account that attributes may reside
in the hwmon directory (/sys/class/hwmon/hwmonX) _or_ in the device
directory (/sys/class/hwmon/hwmonX/device). There is no guarantee that
the raw path doesn't change from release to release; that is what the
symlinks are for. Actually, I have seen the raw platform device path
change over time, so I am surprised that this never affected you.
Well, using the raw platform device path was a bad design decision.
But I still see a difference. In v3.8 all the temp* nodes were in
/sys/class/hwmon/hwmon0/device/ but in v4.4 I can see that they are in
/sys/class/hwmon/hwmon0/. So if we do modify the code, then we still
need to have two versions of userspace code based on the kernel.
Your code should check for the 'name' attribute in both locations.
Guenter
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