Subject: Re: wedges and DEV_BSIZE (Was Re: removing VOPs)
To: Jason Thorpe <firstname.lastname@example.org>
From: David Laight <email@example.com>
Date: 10/10/2005 16:55:59
On Sat, Oct 08, 2005 at 02:37:21PM +0200, Reinoud Zandijk wrote:
> Wouldn't it then be the time to also scrap the fixed DEV_BSIZE blocksize
> interface to discs to replace it with a *sector-size* oriented interface so
> various filingsystems like msdosfs and udf eventually can support non 512
> bytes/sector filingsystems?
> There has been several patches around for yonks that fixes these issues but
> they were never integrated. Our msdosfs f.e. doesn't support non 512
> bytes/sector devices.
One problem is working out which numbers have to change with the physical
sector size, and which don't.
Provided the logical sector size (or FFS fragment size) is a multiple of
the physical sector size, the physical size doesn't really matter.
One option is to make all the filesystem values that refer to 'sectors'
actually refer to 'units of 512 bytes'. Then it becomes possible to use
'dd' (etc) to copy a filesystem from a phyical media with one sector size
to another with a different size.
Apart from ensuring that programs (like installboot, and disklabel) use large
enough transfers, not much goes wrong.
The difficulty is supporting disks labelled by other OS.
Do you know what the 'extended partition chain' should look like on a
disk with 2k physical sectors?
David Laight: firstname.lastname@example.org