get device sysfs path ioctl (was: Re: What to do about the 2TB limit on HDIO_GETGEO ?)

["Dan Williams" <dan.j.williams@intel.com>]

[ adding Neil to the cc ]

On Tue, Mar 25, 2008 at 2:26 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> Greg KH wrote:
>  > On Tue, Mar 25, 2008 at 01:36:51PM -0700, H. Peter Anvin wrote:
>  >> Randy Dunlap wrote:
>  >>>> Come on people, adding symlinks for device major:minor numbers in sysfs
>  >>>> to save a few 10s of lines of userspace code?  Can things get sillier?
>  >>>>
>  >>>> You can add a single udev rule to probably build these in a tree in /dev
>  >>>> if you really need such a thing...
>  >>>>
>  >>>> And what's wrong with your new ioctl recomendation?
>  >>> Ah, there's some sanity.  :)
>  >> It's not so much an issue of a few tens of lines of user space code, but
>  >> rather the fact that something that should be O(1) is currently O(n).
>  >
>  > "should"?  why?  Is this some new requirement that everyone needs?  I've
>  > _never_ seen anyone ask for the ability to find sysfs devices by
>  > major:minor number in O(1) time.  Is this somehow a place where such
>  > optimization is warranted?
>
>  Well, when dealing with shell scripts a O(n) very easily becomes O(n^2).
>   For the stuff that I, personally, do, it's not a big deal, but people
>  with large number of disks have serious gripes with our boot times.
>

I will jump in here to point out there would be another user of such
an interface.  Neil proposed an ioctl to retrieve the sysfs path of a
device as part of his md support for external metadata.

Neil's initial patch:
http://marc.info/?l=linux-raid&m=119761445714319&w=2

My attempt to push things along:
http://marc.info/?l=linux-kernel&m=120132398120816&w=2

--
Dan