From: Linus Torvalds <torvalds@transmeta.com>
To: Steven Dake <sdake@mvista.com>
Cc: Werner Almesberger <wa@almesberger.net>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] udev enhancements to use kernel event queue
Date: Thu, 19 Jun 2003 17:43:26 -0700 (PDT) [thread overview]
Message-ID: <Pine.LNX.4.44.0306191717120.1987-100000@home.transmeta.com> (raw)
In-Reply-To: <3EF250EF.1010802@mvista.com>
On Thu, 19 Jun 2003, Steven Dake wrote:
>
> Serialization is important for the case of a device state change
> occuring rapidly. An example is a device add and then remove, which
> results in (if out of order) the add occuring after the remove, leaving
> a dead device node in the filesystem. This is tolerable. What isn't as
> tolerable is a remove and then an add, where the add occurs out of order
> first. In this case, a device node should exist on the filesystem, but
> instead doesn't because the remove has come along and removed it.
This still isn't a global serialization thing, though. For example,
there's no reason _another_ device should be serialized with the disk
discovery.
And there are lots and lots of reasons why they should not EVER be
serialized, especially since full serialization (like through a shared
event deamon) results is _serious_ problems if one of the events end up
being a slow thing that needs to query and/or spin up hardware.
In other words, once you start talking about device nodes, you really want
to handle the serialization on a per-node basis. Having some kind of
kernel support for that is quite possible a good idea, but care should be
taken that non-dependent events shouldn't be serialized.
An easy way to do partial serialization is something like this:
- each "call_usermodehelper()" gets associated with two numbers: the
"class number" and the "sequence number within a class". We keep track
of outstanding usermodehelpers.
Add the class and sequence number to the environment of the hotplug
execution so that the user-mode hotplug code can query them.
- we add a simple interface to allow a user mode helper to ask the kernel
to "please wait until class X has no pending sequence numbers smaller
than Y"
See what I'm aiming at? The class numbers shouldn't have any particular
meaning, they're just a random number (it might be the bus number of the
device that hotplugged, for example). But this allows a hotplug thing to
say "if there are other outstanding hotplug things in my class that were
started before me, wait here".
Linus
next prev parent reply other threads:[~2003-06-20 0:29 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-06-12 19:10 [PATCH] udev enhancements to use kernel event queue Steven Dake
2003-06-12 21:47 ` Patrick Mochel
2003-06-13 16:31 ` Steven Dake
2003-06-13 17:06 ` Patrick Mochel
2003-06-12 21:47 ` Greg KH
2003-06-12 22:03 ` Andrew Morton
2003-06-12 22:50 ` Greg KH
2003-06-12 22:51 ` Andrew Morton
2003-06-12 23:02 ` Greg KH
2003-06-12 23:09 ` Greg KH
2003-06-12 23:14 ` Patrick Mochel
2003-06-12 23:16 ` Robert Love
2003-06-12 23:25 ` Greg KH
2003-06-13 20:01 ` Oliver Neukum
2003-06-18 22:59 ` Greg KH
2003-06-19 0:12 ` Kevin P. Fleming
2003-06-19 0:20 ` Greg KH
2003-06-19 0:42 ` Kevin P. Fleming
2003-06-19 0:51 ` Greg KH
2003-06-19 0:25 ` Andrew Morton
2003-06-19 6:27 ` Oliver Neukum
2003-06-12 23:25 ` Patrick Mochel
2003-06-12 23:29 ` Robert Love
2003-06-12 23:32 ` Greg KH
2003-06-12 23:34 ` Patrick Mochel
2003-06-12 23:40 ` Paul Mackerras
2003-06-12 23:50 ` Robert Love
2003-06-13 12:44 ` Richard B. Johnson
2003-06-13 12:54 ` Olivier Galibert
2003-06-12 23:52 ` Patrick Mochel
2003-06-13 8:41 ` Alan Cox
2003-06-13 11:00 ` Paul Mackerras
2003-06-13 11:07 ` Herbert Xu
2003-06-13 13:31 ` Alan Cox
2003-06-13 19:57 ` Joe Korty
2003-06-13 21:10 ` Alan Cox
2003-06-13 11:17 ` David Schwartz
2003-06-13 15:44 ` Davide Libenzi
2003-06-12 23:42 ` Robert Love
2003-06-12 23:45 ` Davide Libenzi
2003-06-12 23:05 ` Robert Love
2003-06-19 19:51 ` Werner Almesberger
2003-06-26 12:17 ` Tommi Virtanen
2003-06-26 14:35 ` Werner Almesberger
2003-06-13 8:40 ` Alan Cox
2003-06-13 9:14 ` Olivier Galibert
2003-06-19 20:53 ` Werner Almesberger
2003-06-13 16:05 ` Steven Dake
2003-06-13 16:32 ` Greg KH
2003-06-13 15:51 ` Steven Dake
2003-06-13 16:41 ` Patrick Mochel
2003-06-13 16:42 ` Greg KH
2003-06-13 17:17 ` Chris Friesen
2003-06-12 22:27 ` Oliver Neukum
2003-06-13 16:03 ` Steven Dake
2003-06-13 16:50 ` Patrick Mochel
2003-06-13 17:10 ` Steven Dake
2003-06-13 18:26 ` Greg KH
2003-06-13 19:02 ` Patrick Mansfield
2003-06-13 17:32 ` Oliver Neukum
2003-06-13 18:23 ` Greg KH
2003-06-13 18:24 ` Greg KH
2003-06-13 7:17 ` Christoph Hellwig
2003-06-13 18:06 ` Linus Torvalds
2003-06-19 23:32 ` Werner Almesberger
2003-06-19 23:42 ` Steven Dake
2003-06-20 0:05 ` Linus Torvalds
2003-06-20 0:10 ` Steven Dake
2003-06-20 0:43 ` Linus Torvalds [this message]
2003-06-20 2:26 ` Werner Almesberger
2003-06-20 17:03 ` Steven Dake
2003-06-20 17:18 ` Patrick Mochel
2003-06-14 6:36 John Bradford
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