On Tue, 2004-07-06 at 18:38 -0400, Jeremy Katz wrote: > On Tue, 2004-07-06 at 18:17 +0200, Owen Taylor wrote: > > On Tue, 2004-07-06 at 22:28, Jeremy Katz wrote: > > The value of it on the case of the writable root filesystem is that > > you only have one path for how the system works, not two. Changes > > to device naming only have to be put into one place. Eventually we > > can simple drop the dev package and it's 18,000 files. > > But exactly what does the 18k files cost it? Similarly, we could drop > ldconfig runs in %post and just have all of the symlinks created on each > boot, but that doesn't strike me as a good idea either. It's a useful > optimization to have them laid down by the install because then you > never have to create new device nodes. Which can be a lot of device > nodes per device. Changes to device naming is simple -- just make what > gets used for the creation the same as what gets used in the dev > package's spec file. Nice and simple to do with current infrastructure. > One very useful feature that is not readily available in current infrastructure is that udev maintains a database. This allows reverse lookup into sysfs, e.g. given device node /dev/sda you can very easily determine what physical device this device node corresponds to. And you can also go the other way [1]. With the infrastructure available today (e.g. static dev), you'd have to search either for the right major:minor in /dev or find the right 'dev' file in sysfs which would be insanely expensive. > > > My bigger concern is that udev has _zero_ policy. It basically is a > > > "well, we want to let people do what they want" system. Which is no > > > better than doing nothing at all. Which may actually be good in a way as it discourages developers to assume that e.g. /dev/cdrom is the (default) optical drive, /dev/dsp is the (default) audio device etc. Heh, so to fully test it we'd just select a new naming scheme on every reboot :-) But, yeah, you're right, there's so many legacy applications out there that relies on device node naming policies, and I do understand that this is not necessarily bad. Though it would be nice they did the right thing, at least for desktop applications. Cheers, David [1] : [david@ixus david]$ udevinfo -q path -n /dev/sda /block/sda [david@ixus david]$ ls -l /sys/block/sda/device lrwxrwxrwx 1 root root 0 Jul 6 19:17 /sys/block/sda/device -> ../../ devices/pci0000:00/0000:00:10.0/0000:02:07.2/usb1/1-1/1-1.2/1-1.2:1.0/ host9/9:0:0:0 [david@ixus david]$ udevinfo -r -q name -p /sys/block/sda /dev/sda
