On Wed, Mar 26, 2008 at 1:54 AM, Tejun Heo <htejun@xxxxxxxxx> wrote: > Mark Lord wrote: > > So have we. sysfs is a total nightmare to extract information from > > under program / script control. The idea presented in this thread, > > is to have it cross-index the contents with a method that actually > > makes it easy to access in many common scenarios, without requiring > > huge gobs of code in user space. Or in kernel space. > > > > And it's not just a few 10s of lines of code currently, > > but rather about 80-100 lines just to find the correct device subdir, > > and *then* a few more 10s of lines of code to retrieve the value. > > > > In a bulletproof fashion, that is. Sure it can be slightly smaller > > if niceties such as error checking/handling are omitted. > > > > There's no guarantee that udev is present, and even if it were present, > > there's no guarantee that the names in /dev/ will match /sysfs/ pathnames, > > since udev is very configurable to do otherwise. > > > > So lookups are by dev_t, which sysfs has no simple or even easy way > > of accomplishing. O(n) at a minimum. > > > > If we make it easier to access, then more programs will use it > > rather than us having to expand our tricky binary ioctl interfaces. > > > > Isn't that part of the idea of sysfs -- to limit the need for new ioctls ? > > The questions are... > > 1. Are we gonna push sysfs as the primary interface and not provide an > alternative interface (ioctl here) which can provide equivalent > information? There are people running their systems w/o sysfs but I > think we're getting closer to this everyday. > > 2. Is udev an essential part of all systems? I'm not sure about this > one. Lots of small machines run w/o udev and I think udev is a bit too > high level to depend on for every system. > > If both #1 and #2 are true, I agree with Mark that we need an easy to > map from device number to matching sysfs nodes. Tools which are used > early during boot and emergency sessions need this mapping and many of > them are minimal C program w/o much dependency for a good reason. > Requiring each of them to implement their own way to map device node to > sysfs node is too awkward. > > Probably something like /sys/class/block/MAJ:MIN "Devices directories" are not supposed to contain duplicate entries. It would slow-down, or may even break things. > or /sys/class/devnums/bMAJ:MIN? These are no devices belonging to the class "devnums", so it may confuse things which crawl these directories to get "all devices". Current coldplug-like setups will likely add duplicate devices with the wrong subsystem. There are also bus-devices with have a dev_t, and that will make them show up in /sys/class, which might confuse some tools too. I guess we will need to find some other solution as a /sys/class/ for that. And we must prefix the links with 'c' and 'b' because dev_t is not unique across char and block devices. Thanks, Kay -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
