Re: scsi naming (was: devfs patch v3)
Richard Gooch (rgooch@atnf.CSIRO.AU)
Mon, 12 Jan 1998 09:06:24 +1100
James Mastros writes:
> On Mon, 12 Jan 1998, Richard Gooch wrote:
> > James Mastros writes:
> > > [...]
> > > I should think that we want them as deep as we can go. After-all, there is
> > > an overhead of one dentry and one inode in memory for each one, but we only
> > > have that overhead for directories that we acatually have... So my
> > > suggested directory structure looks like:
> > >
> > > SCSI/
> > > c/
> > > controller
> > > b/
> > > bus
> > > id/
> > > id
> > > lun/
> > > lun
> > > partition
> > >
> > > (where the direcories c, b, id, and lun (and the node partition) are
> > > numbers, and the nodes controller, bus, id, and lun are nodes for ioctls
> > > that effect the entire controller, bus, id, or lun). Indeed, perhaps the
> > > partitions should be directories that mirror the partition structure on-disk
> > > (so exteneded dos partitions would be directories.) Note that my scheme
> > > dosn't diferincate between hard-drives, tape-drives, cdrom-drives, and
> > > generics -- I think that they should be merged: does anybody know why they
> > > weren't in the first place? (I don't have any SCSI devices, so I don't
> > > really know.)
> >
> > Firstly, I think the entire SCSI disc should be a file: reading and
> > writing directories seems not to be the done thing. I note that ext2
> > disallows reading of directories, and the VFS disallows opening of
> > directories in write mode.
>
> Huha? My plan has the disk as one node, just like every other plan. I have
> a node for the whole controller, bus, id and lun as well (the current scheme
> has a whole-lun = whole-disk node, but none of the others. Then, within
> each controller, there is a directory for each bus. (similar for bus->id,
> id->lun, lun->partition). That is to say, the node for the 1st bus on the
> 1st controller is SCSI/1/1/bus. The whole disk of the 2nd lun on the 3rd
> device on the 4th bus of the 5th controller is SCSI/5/4/3/2/lun. Etc, etc...)
OK, sorry, I misunderstood.
> > Secondly, take drives don't have partitions. I dunno about CD-ROMS.
> Exactly; that's what the SCSI/c/b/i/l/lun is for. The whole lun is the
> whole disk, regardless of if it has partitions on it or not.
>
> > Thirdly, I think you *want* to differentiate between hard discs and
> > tape drives, at a fairly high level. "What tape drives do I have?"
> > Looking for one tape driver amongst 100 SCSI discs is like looking for
> > a needle in a haystack.
>
> Why not simply have an "indetify" ioctl?
Because I want it to be obvious from the entries in /dev, just using
<ls>. Perhaps we could support your system *in addition* to one that
differentiates between SCSI types. But that costs more devfs
inodes...
Regards,
Richard....