Re: devfs rants & raves
> Er, how does devfs do anything different with "swappable" CDs? The
> CD player's device does not change with the insertion or removal of
> CDs.
I'm not talking about changing disks, I'm talking about swapping out
CD drives. I find it extremely useful to be able to add a CD or tape
drive at runtime and know (based on its bus/ID) exactly where it'll
show up.
Do people really add new drives like this? Maybe not everybody, but some
of us do. And with the plethora of new portable CD/disk/CDRW/tape things
out that are designed to connect to laptops via parallel, USB, or some
wierd IDE PCMCIA card, this is going to become more prevalent.
> I can see it in the case of hot swappable scsi drives with SCA
> type bus, but usually these are run as fixed id's per slot so all
> you have to do is put the drives in the slots to get the /dev/sdX
> designations to come out the way you want.
True, hot-swap SCSI disks most likely will have a fixed ID per slot. If
you have 12 slots, but only 3 disks at boot time, you get /dev/sda[a-c].
If you then add disks they'll be /dev/sd[d-l]. That'll change, though,
next time you reboot. All disks will get reassigned names based on IDs,
so you either have to arrange your disks to match the name-to-ID mapping
(not always convienient) or pass a lot of arcane options to the SCSI
driver to control the mapping. Much easier to use devfs.
> and also they are usually run as raid devices which also aren't sensitive
> in this way.
Linux software RAID. Some people actually use it. devfs is convienient.
> the USB bus
> could have it's own devfs like /dev/usb/whatever for people who live
> for that kind of pain ~:^) But then how does that interact with the
> /dev/input layer for input devices and so on?
> > With devfs I can finally add a SCSI target
> > in the middle of my chain and not have half my disks change their device
> > names.
> Um, what? So what you're sayin' is that we all have to be saddled
> with the scourge that is devfs because you're too lazy to properly
> set your scsi id's in order to get your /dev designations to come
> out right?
No, I'm saying that devfs is a really useful thing, especially on systems
with assloads of peripherals. It works for me. If you don't like it,
DON'T BUILD IT INTO YOUR KERNEL. Ah, the beauty of open-source software...
> SCSI lun's are almost never used except in juke boxes
> and possibly certain kinds of tape drives.
Who's talking about SCSI luns? I'm talking about SCSI and IDE IDs, but
maybe you're referring to the lun part of a devfs name. I like having the
lun info available; it makes it really handy for certain types of SCSI to
IDE bridges, as well as CD jukeboxes and tape libraries. Just because you
don't have such hardware doesn't mean that no one else does. Again, if you
don't like it, DON'T BUILD IT INTO YOUR KERNEL.
Yes, devfs names are longer. Personally, I don't care; the only time I
type them out is when I'm adding stuff to my fstab or automounter. Some of
us really appreciate the static names, though. And the only way we're
gonna get this (under Linux, at least; most commercial UNIXes have this,
and others have said OpenBSD has a way to do this) is to use devfs. I
hope it stays in the kernel. If not, I'm going to keep applying the devfs
patches. I think Mr. Gooch has done some very useful work.
--
Mike Shuey
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