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RE: [ogfs-dev]Journal info ... device number




> -----Original Message-----
> From: domthera [mailto:stefan.domthera@schlund.de]
> Sent: Wednesday, July 23, 2003 5:44 AM
> To: opengfs-devel@lists.sourceforge.net
> Subject: Re: [ogfs-dev]Journal info

> > > Wouldn't a device *number* potentially change from time to time?
> >
> > Possibly.
> 
> Major numbers in the official kernel tree are defined in
> Documentation/devices.txt. They don't change.
> It is possible to request dynamic (unused) major numbers during device
> registration. This should be used in private
> device drivers only.
> The minor numbers are managed by the device drivers, chaos 
> would reign in
> ext3 if these numbers change.

I'm mystified . . . minor numbers might not change during a Linux session (between boot up and shutdown), but I'm pretty sure they can change due to adding/removing devices, etc. between sessions . . . that's a problem that pool and EVMS solve, presenting a consistent /dev name even if the numbers change (they both write a header on the disk to identify the disk, no matter what its device number is ... the header is persistent across reboots).

Looking at man page for mke2fs (RedHat 8.0), it says you can specify an external journal by one of 3 ways:

-- device name
-- volume label
-- UUID (stored in ext2 superblock on journal device)

The device name might not be persistent between boots (any more than a minor number might be), but the other two should be.  

If the superblock contains a device number, might it be written to the superblock at mount time???

-- Ben --

Opinions are mine, not Intel's

> Stefan
> 


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