On Thu, May 18, 2000 at 05:37:17PM +0200, Trond Myklebust wrote:
> >>>>> " " == ferret <ferret@phonewave.net> writes:
>
> > -----BEGIN PGP SIGNED MESSAGE----- Ah, you mean a regular file
> > on an NFS mount cannot be treated as a block device by the
> > 2.2.x loopback device?
>
> If you like. The 2.2.x loopback device uses the 'bmap()' inode
> operation to map the file into 'blocks'.
> If I understand correctly, this is a function that maps to the
> physical location of the files on the underlying disk. It use in the
> loopback device was apparently motivated by the needs of encryption
> modules.
>
> Under 2.3.x the loop device uses the generic file read/write routines,
> instead, and leaves it up to the encryption modules to call bmap() if
> needed. Those modules still won't work under NFS in 2.3.x.
>
I'm not sure why 2.2 uses bmap(), maybe for speed. Yes, the crypto
layer can use information about the absolute offset of a block for
encryption purposes, but this feature was added because it was
available in the loop implementation, not the other way around.
astor
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