[dm-devel] [PATCH] clear seg valid when resetting bi_idx

[Mike Christie]

Mike Christie wrote:
> In __end_that_request_first if the bio is partially completed 
> blk_recalc_rq_segments will reset the segment values. If the bio is 
> later remapped and resent becuase of an error, we restore bi_idx but the 
> segment values are left to the partially completed state causing many 
> fun problems when blk_rq_map_sg is called in SCSI.
> 
> The attached patch clears the BIO_SEG_VALID bit, so the segment values 
> are recalculated when it is resent. It was built and tested against 
> 2.6.4-udm1.
> 
> Mike Christie
> 
> 
> ------------------------------------------------------------------------
> 
> --- linux-2.6.4-rc1-udm1.orig/drivers/md/dm-bio-record.h	2004-03-03 19:56:43.000000000 -0800
> +++ linux-2.6.4-rc1-udm1/drivers/md/dm-bio-record.h	2004-03-03 20:50:58.645821621 -0800
> @@ -37,6 +37,7 @@ static inline void dm_bio_restore(struct
>  	bio->bi_bdev = bd->bi_bdev;
>  	bio->bi_size = bd->bi_size;
>  	bio->bi_idx = bd->bi_idx;
> +	bio->bi_flags &= ~(1 << BIO_SEG_VALID);
>  }
>  
>  #endif


I don't think this is 100% correct. It gets the correct number of 
segments counted so no oops from SCSI, but when we resend it the 
bio_vec's bv_offset and bv_len would sitll be in the state 
__end_that_request_direst left them.

Would it be ok to just add a curr_bv_offset and curr_bv_len to the bio 
that is writeable leaving the bio_vec readonly, or is the correct fix 
for DM to do a deep record of the bio?