From: David Brownell <david-b@pacbell.net>
To: linux-hotplug@vger.kernel.org
Subject: Re: hotplug (was devfs)
Date: Wed, 13 Nov 2002 15:14:46 +0000 [thread overview]
Message-ID: <marc-linux-hotplug-103720035306943@msgid-missing> (raw)
In-Reply-To: <marc-linux-hotplug-103719698302880@msgid-missing>
Oliver.Neukum@lrz.uni-muenchen.de wrote:
> On Wed, 13 Nov 2002, Nick Craig-Wood wrote:
>
>>We have machines with 6 x 4 port USB <-> serial converters attached.
>>These would get randomly assigned usb device ids and hence random
>>/dev/ttyUSB nodes. Not very useful when there is a load of different
>>things attached to the 24 serial ports!
Right, this is why "physical" paths are needed as well as
sequentially assigned /dev/...N nodes.
>>Sometimes we also found that one of the devices wouldn't get
>>initialised properly.
>>
>>We fixed these problems by removing hotplug and loading the relevant
>>kernel modules in the correct order and voila a perfectly
>
> Modules ? Plural?
Sounds like a better fix might have been to teach hotplug
about your additional modules... or to fix the modules
so they initialized correctly!
>>So - perhaps hotplug ought to be serialised?
>
>
> Definitely, but how far?
Until about the last week before 2.4.0final shipped, hotplug
was serialized. The serialization got removed at the same
time keventd got added.
Why was it removed? Because serializing meant that kernel
locks had to be held until a user mode program returned.
That caused deadlock when, for example, network hotplug
had to grab that same lock ... it basically wasn't possible
to get away from that problem in at least that case, and by
extension likely other cases.
So I'm not sure I see hotplug ever getting serialized.
But then, I don't see any reason it would ever fix the
problem of needing to map /dev/... nodes to the physical
device they represent, either.
- Dave
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next prev parent reply other threads:[~2002-11-13 15:14 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-11-13 14:15 hotplug (was devfs) Oliver.Neukum
2002-11-13 15:14 ` David Brownell [this message]
2002-11-13 15:48 ` Nick Craig-Wood
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