From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Korsgaard Date: Wed, 08 Sep 2010 17:07:33 +0200 Subject: [Buildroot] mdev handling In-Reply-To: <201009081648.41500.yann.morin.1998@anciens.enib.fr> (Yann E. MORIN's message of "Wed, 8 Sep 2010 16:48:41 +0200") References: <87occ8cnr8.fsf@macbook.be.48ers.dk> <201009081648.41500.yann.morin.1998@anciens.enib.fr> Message-ID: <87k4mwclze.fsf@macbook.be.48ers.dk> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: buildroot@busybox.net >>>>> "Yann" == Yann E MORIN writes: Hi, >> Isn't this largely obsolete now we have devtmpfs? Yann> Well, devtmpfs has a static naming scheme, default permissions for device Yann> nodes, so it is not sufficient by itself. As the help entry for devtmpfs Yann> states: Yann> "It provides a fully functional /dev directory, where usually Yann> udev runs on top, managing permissions and adding meaningful Yann> symlinks." True, but it is fine for most small embedded systems as well (E.G. the target group of buildroot). Most of these are root only so you just want the device nodes of the hw you have available. But yes, it can certainly be used with mdev as well (you basically just get rid of the slow mdev -s at startup). Yann> Even better, embedded system have a mostly static set of devices, thus a Yann> mostly static set of entries in /dev, and those can go to flash. Entries Yann> for removeable devices (eg. usb sticks) can still go there. Thus you gain Yann> both in flash (no space used by any code, kerenl or userland) and in RAM Yann> (no space used by devtmpfs/tmpfs/ramfs/... and VFS entries). The devtmpfs code is very small if you already have ramfs/tmpfs (and most likely you do), so the size difference between devtmpfs and static /dev is really down in the noise. Yann> Really, devtmpfs and mdev/udev are for desktop, where the set of Yann> devices is to easily divergent, IMHO... Depends on what you want to do. You fairly often see embedded devicess that react when you plug in a usb device. For that, mdev (or other hotplug scripts) are pretty nice. -- Bye, Peter Korsgaard