On Fri, Apr 27, 2012 at 10:14 AM, Lucas De Marchi <[email protected]> wrote: > > Hi Wolfgang > > On Fri, Apr 27, 2012 at 3:47 AM, Wolfgang Denk <[email protected]> wrote: > > > > Dear Lucas De Marchi, > > > > In message > > <camow1v5yncyx1qri5nyu2k_q6gabj-frm1b8a7wsvcbmrxa...@mail.gmail.com> you > > wrote: > > > > > > Caching of information on udev > > > > > > ; Summary: Caching device information on udev > > > > > > ; Proposer: Lucas De Marchi ([email protected]) > > > > Yocto uses this feature in a number of configurations; it creates an > > archive "/etc/dev.tar" on the first boot and, if this archive exists > > during the next boot, it gets extracted and most of the coldplug > > events are filtered. Only if the archive does not exist a full scan is > > performed. > > I didn't know this existed, but IMO is the wrong approach. If all you > want is a static /dev, you could have that partition already done, > without untar anything.
This was an ugly hack used by many distros, not just yocto but also Gentoo. devtmpfs anyone? :-) > > This accelerates booting in static configurations, but also causes > > problems because cold plugged devices may not get detected (see > > > > > > http://www.denx.de/wiki/view/ELDK-5/FrequentlyAskedQuestionsAndAnswers#Missing_Device_Files_for_Cold_Pl) > > Yeah, that's one of the reasons I'm not proposing something like this. > Instead we are proposing to modify udev to let it builtin handle its > own cache. For modules, this can be used to load all modules at once. > This infrastructure can be used to replay the links in /dev too. > Remind that recent versions of udev doesn't create nodes in /dev > anymore. That's right. It's not about device nodes, but also loaded modules, blkid information and so on. Imagine udev would report the same tree from the last run as well, it would know disk labels, etc. > > > == Scope == > > > # Implementation: 2 weeks > > > # Benchmark creation: 1 week > > > # Adapt to community feedback, tests and upstream: 2 weeks > > > > This appears to be way to high. All that needs to be done is using a > > Yocto based file system :-) > > A bit high because it's a different thing from what you are talking about > ;-) Yes, and really there are some concerns that must be addressed: - where to store this? we need it to be available early otherwise it's useless. - how to detect and invalidate the cache? It would be good if desktops/laptops could use it as well, avoiding the feature to be broken or forgotten by people. - have it measured and accepted by the upstream... which will not be a simple task ;-) -- Gustavo Sverzut Barbieri http://profusion.mobi embedded systems -------------------------------------- MSN: [email protected] Skype: gsbarbieri Mobile: +55 (19) 9225-2202 _______________________________________________ Celinux-dev mailing list [email protected] https://lists.celinuxforum.org/mailman/listinfo/celinux-dev
