[ adding Neil to the cc ]

On Tue, Mar 25, 2008 at 2:26 PM, H. Peter Anvin 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:

My attempt to push things along:

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