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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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