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DragonFly kernel List (threaded) for 2004-04
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Re: devfs vs udev/hotplug

From: esmith <esmith@xxxxxxxxxxxx>
Date: Thu, 22 Apr 2004 08:39:36 -0400


It seems there is one other approach that is very similar to udev called "User-Space System Device Enumeration" or uDSE. The uSDE was built in response to a set of telco and embedded community requirements. The uDSE is based around the idea of policies.


According to one of the developers, issues that uDSE addresses that udev might not are:

* The embracing of all device types with no specialization or limitation.
* The ability to have total control over the handling a device via external policy programs. Policy programs are invoked with a formal command line and description of the event that caused there invocation.
* The "service container" concept. A device is classified (or recognized by a pattern match) and this raises an (queued) event which is caught by a configurable "service container". The container is an ordered list of handlers that process the device.
* Event queuing and aggregation. Minimizing the number of program invocations (fork/exec) is critical in embedded environments - small processors.
* Aggressive device enumeration. Multiple concurrent policy execution and management.
* Device information persistence is a function of device policies, not the enumeration framework.There are many situation where persistence is not an issue at all or only in specific cases (like disks). Why always pay for the memory/disk, for persistence, when it is not (always) necessary?
* Transactional protection of multiple configuration files is necessary. Multiple configuration files must often be modified in unison and insurance is necessary that an accurate and correct set of data is used when processing devices.

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