[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Sheflug] Where is /dev/eth0 ? What are major & minor device numbers?



On 08 Jun 2002 07:51:25 +0100
Alex Hudson <home [at] alexhudson.com> wrote:

> On Sat, 2002-06-08 at 00:33, Andrew Basterfield wrote:
> > So what would happen if you have devfs and more than 128 (IIRC) SCSI
> > disks?
> 
> I would extend the kernel to handle more, just like RedHat do now, and
> did previously when the limit was 16. 

And then you hope Linus doesn't allocate your new SCSI block numbers
elsewhere. Redhat can get away with this because they have a huge amount
of influence on Linux development.

> > If you mount a filesystems using NFS it will have no associated /dev
> > entry (and hence no majors and minors).
> 
> That argument doesn't follow, I'm afraid. I'm pretty sure NFS clients
> get their device numbers from the server - which is why, if you move
> an export from one filesystem to another, all the clients need to
> remount.

So does it return the device number from the server (in which case if
the server returns block-8-1 how does it differentiate between /dev/sda1
mounted via NFS and local /dev/sda1) or does it return a unique number
(which would require a major/minor allocation space which NFS
filesystems don't have in linux/Documentation/devices.txt)?

I believe NFS mounted filesystems don't have conventional device
numbers.

> > This doesn't seem to bother 'find' (or indeed any other POSIX
> > utility).
> 
> Really. From the FAQ:
> 
> "Please note that using dynamically allocated block device numbers may
> break the NFS daemons [when the numbers change]" (see above :)
> 
> If the NFS daemons break, I suspect very much that the file utilities
> will also not work. 

The point was that 'find' seemed to be perfectly happy on an NFS
filesystem (assuming they have no associated major/minor number) as do
all other POSIX utilities (in fact they have to work in case / is on
NFS).

> all that means is that you can't pre-encode the major/minor numbers
> you're interested in (both kernel-side or client-side). 

You can still pre-encode [force] block numbers kernel-side with devfs,
should you want to. You have never had the option of pre-encoding the
block numbers in userland [client-side??].

--Andrew

-- 
sparc sun4c stuff:
	http://www.lostgeneration.freeserve.co.uk/sparc
PGP key for list [at] lostgeneration.freeserve.co.uk:
	http://www.lostgeneration.freeserve.co.uk/list.freeserve.co.uk.asc

Attachment: pgp00003.pgp
Description: PGP signature