mdev with hda's

David Henderson dhenderson at
Wed May 11 20:24:04 UTC 2011

On 05/11/2011 04:09 PM, Harald Becker wrote:
>   Hallo David!
>> Realizing this now, I think the PATH variable should be added to the
>> "standard" set of variables as part of the mdev environment.  However,
>> this value would need to be passed by the actual shell PATH and not a
>> pre-defined one from mdev.  I noticed that this was the case while
>> running tests over the last couple of days.
> mdev calls /bin/sh to execute the commands specified in mdev.conf. In
> such situations it is good and well known practice to set PATH to the
> required value at start of the script. The only other default would be
> to use the default path (/bin:/sbin:/usr/bin:/usr/sbin) when calling
> helper scripts. That could be a wise decision for mdev. No other value
> of PATH is reliable at this point, as it has been revealed that mdev
> itself has no direct access to a reliable parent environment.
> To summarize (as I see it now):
> Your question about insane environment setting of mdev is based on the
> wrong assumtion, that mdev reliable propagates the values you are
> seeking for into environment variables, as udev may do. Currently mdev
> exports only MDEV and SUBSYSTEM (where only MDEV is documented). No
> other variables shall be expected to hold any reliable value within
> helper scripts. That is the answer based on current mdev implementation.
> ... but you are right, that it could be a good decision to extend the
> functionality of mdev to export more informations to helper scripts via
> environment variables. At least the values of MAJOR, MINOR and DEVPATH
> shall be accessible within mdev at the point of script invocation
> (assumption based on my short dig into mdev source). Beside this setting
> of PATH to a default value would be wise, and additionally clearing out
> the rest of the environment for helper scripts could be a good decision
> and will help to avoid confusion like David's ... IMHO
> --
> Harald
> _______________________________________________
> busybox mailing list
> busybox at

Agreed.  I think having a standard set of environment variables (even if 
it's a slightly larger set than MDEV and SUBSYSTEM) would be valuable to 
developers and would reduce the amount of work to "reinvent the wheel" 
so-to-speak everytime for those that use scripts.  I can help anyone who 
can code a patch on where to locate some of this information within 
sysfs, however, this will result in mdev having an increasing dependence 
on it.

Thanks again Harald for your continued help!


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