On Tue, Nov 29, 2005 at 11:29:00PM +0000, reinoud@netbsd.org wrote:
> VOP_STRATEGY buffers
> --------------------
> vop_strategy buffers are passed from genfs in 
> sys/miscfs/genfs/genfs_vnops.c:836's VOP_TRATEGY call and created at either 
> line 673 or at line 810 of the same file. In the buffer `mbp' created at 
> line 673, all seems OK but at the buffer `bp' created at line 810, 
> bp->b_bufsize is not initialised and thus ZERO!!!! quite a violation.

the b_bufsize is for the caching usage of struct buf,
not the I/O descriptor usage.  device drivers should not look at it
(and neither should file systems for that matter).


> bread buffers
> -------------
> vop_strategy buffers are passed from bread() in sys/kern/vfs_bio.c's 
> bio_doread() at line 597's VOP_STRATEGY().
> 
> These buffers are claimed/looked up just before in line 577's getblk(). 
> When passed to UDF's vop_strategy() bp->b_resid is undefined though mostly 
> ZERO. Also not according to the struct buf's specs wich would suggest the 
> number of bytes to be read/written in/from the buffer to be bp->b_resid.

b_resid is a return value, it is initialized by the device driver
before it calls biodone().


> Other filingsystems
> ----------
> Filingsystems seem to cope with it by passing the buffers directly to the 
> device layer that aparently ignores most of the buf contents and only 
> reacts to bp->b_count.
> 
> Filingsystems that do care about the buffer contents are also only looking 
> at bp->b_count.

right, this is by design.


as other people have also said, none of the behaviours you've described
are bugs.

-Chuck