mdev with hda's

David Henderson dhenderson at digital-pipe.com
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
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> busybox at busybox.net
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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!

Dave


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