From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Brownell Date: Wed, 13 Nov 2002 15:14:46 +0000 Subject: Re: hotplug (was devfs) Message-Id: List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-hotplug@vger.kernel.org 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 ------------------------------------------------------- This sf.net email is sponsored by: Are you worried about your web server security? Click here for a FREE Thawte Apache SSL Guide and answer your Apache SSL security needs: http://www.gothawte.com/rd523.html _______________________________________________ Linux-hotplug-devel mailing list http://linux-hotplug.sourceforge.net Linux-hotplug-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-hotplug-devel