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SubjectRe: devfs and /proc/ide/hda
AJ Lewis writes:
>
> --CblX+4bnyfN0pR09
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>
> On Thu, Mar 08, 2001 at 01:32:03PM +0100, Goswin Brederlow wrote:
> > > What it should do is change based on whether devfs is mounted
> > > or not. It doesn't make *any* sense to have
> > > /dev/ide/host0/foo/bar in your /proc/partitions entries if you
> > > aren't mounting devfs. The /proc/partitions entry is the only
> > > way I know of for something like LVM to determine which devices
> > > to scan for Volume Groups. If you can't read /proc/partitions,
> > > it has to attempt to scan all block devices it recognizes,
> > > regardless of whether they are actually on the system or not.
> > > This can take several minutes.
> >=20
> > First:
> >=20
> > % cat /proc/partitions=20
> > major minor #blocks name
> >=20
> > 3 0 20010816 ide/host0/bus0/target0/lun0/disc
> > 3 1 192748 ide/host0/bus0/target0/lun0/part1
> > 3 2 249007 ide/host0/bus0/target0/lun0/part2
> > 3 3 1 ide/host0/bus0/target0/lun0/part3
> > 3 5 289138 ide/host0/bus0/target0/lun0/part5
> > 3 6 1951866 ide/host0/bus0/target0/lun0/part6
> > 3 7 979933 ide/host0/bus0/target0/lun0/part7
> > 3 8 16346106 ide/host0/bus0/target0/lun0/part8
> > 33 0 80043264 ide/host2/bus0/target0/lun0/disc
> > 33 1 80035798 ide/host2/bus0/target0/lun0/part1
> >=20
> > So its already right.
>
> Only if devfs is mounted. That's my point. Maybe it's an corner
> case to have devfs compiled into the kernel, but not mounted, and so
> we can just ignore this, but it seems to me that /proc/partitions
> should reflect which /dev system is currently running.

I consider it a corner case. There isn't really an alternative.
Firstly, it would be really messy to magically change the output of
/proc/partitions depending on whether devfs was mounted. Secondly,
just because it's mounted doesn't mean it's mounted on /dev, so it's
still easy to get wrong.

> > Secondly with devfs, why not just scan all /dev/discs/?
> >=20
> > % ls -l /dev/discs=20
> > total 0
> > lr-xr-xr-x 1 root root 30 Jan 1 1970 disc0 -> ../ide/h=
> ost0/bus0/target0/lun0/
> > lr-xr-xr-x 1 root root 30 Jan 1 1970 disc1 -> ../ide/h=
> ost2/bus0/target0/lun0/
> >=20
> > Also if lvm opens all known devices by way of /dev/whatever while
> > scanning, it will only find existing devices there with devfs.
>
> Yeah, as long as devfs is running, that makes sense.

If you want a really robust solution, have your tool scan
/proc/filesystems and see if devfs is available. If not, scan
/proc/partitions. If devfs is available, then create a temporary mount
point and mount it there, then scan $mntpoint/discs.

Regards,

Richard....
Permanent: rgooch@atnf.csiro.au
Current: rgooch@ras.ucalgary.ca
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