Re: [RFC PATCH] Move actually mounting the root filesystem into its own series of hooks.

[Jeremy Katz <katzj-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Tuesday, February 24 2009, Seewer Philippe said:
> Victor Lowther wrote:
> [snip]
>>> - 'dhclient -nw': Why are you starting the dhclient in daemon mode?  
>>> Couldn't that pose problems when dhcp takes ages to acquire an 
>>> adress? I mean like, we've ifup'ed all interfaces and are allready in 
>>> the mount hooks without an ip. I guess we'd have to have a blocking  
>>> mount-script waiting for at least one interface to be really brought  
>>> up or spew an error message after a specific time out.
>>
>> I run it in daemon mode so that udev does not have to wait on it. The  
>> dhclient-script creates a file when the interface is up, and any mounts 
>> that depend on the network can wait for those files to appear. ifup 
>> does the same thing with static interfaces.
>
> I don't like the asynchronousnes of this. This means we have to wait in  
> pre-mount or mount until we have at least one interface up without any  
> knowledge if another might come up later as well.

The problem is that the appearance of devices *is* asynchronous and you
have to keep things as event driven.  That's why originally everything
was being driven off of udev rules rather than hooks.  If you start
trying to do things in hooks and assume synchronous behavior, boot will
be slower and you also can't have, eg, usb devices being used (usb plug
events are always async; anything else is an illusion)

Jeremy
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