On 4 Jun 2002 eeh@netbsd.org wrote:

> | currently every disk driver and almost all of the rest of the system
> | assume b_blkno is in units of DEV_BSIZE, so it would definitely be easier
> | to fix the few places that assume something else than to switch everything
> | that assumes units of DEV_BSIZE.
> |
> | as for FFS, I think the only place it has a problem is in its usage of
> | the fs_fsbtodb field in the superblock.  code that uses this field is
> | attempting to convert from a fragment size to the units of b_blkno,
> | so such code should really just compute the desired value
> | 	(fs->fs_fshift - DEV_BSHIFT)
> | rather than using the value in the superblock.
>
> Where do you do the read-modify-write operations needed to write data in
> increments smaller then the device block size?  And how do you make sure
> you don't get corruption when there are two operations that want to write
> to different DEV_BSIZE parts of a single device block?  Don't forget that
> things like fsck need to be able to do those sorts of operations without
> the benefit of the buffer cache.

As I understand what Chuck did, all i/os have to be in terms of underlying
disk sectors. So you won't get two writes to sub-sector parts because you
can't write less than a sector.

Take care,

Bill