On Fri, 2013-11-29 at 16:42 +0800, majianpeng wrote:
> Make scsi-mq support blk-pc-command.
> 
> Signed-off-by: Jianpeng Ma <majianp...@gmail.com>
> ---
>  drivers/scsi/scsi_lib.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index bed596e..679e840 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1059,9 +1059,11 @@ int scsi_init_io(struct scsi_cmnd *cmd, gfp_t gfp_mask)
>       /*
>        * Use pre-allocation of cmd->sdb scatterlists with scsi-mq..
>        */
> -//FIXME: scsi-mq dif descriptor init within scsi_init_io
>       if (rq->mq_ctx) {
>               BUG_ON(rq->nr_phys_segments > SCSI_MAX_SG_SEGMENTS);
> +             cmd->sdb.table.sgl = cmd->mq_sgl;
> +             cmd->sdb.table.nents = rq->nr_phys_segments;
> +             sg_init_table(cmd->sdb.table.sgl, rq->nr_phys_segments);
>               scsi_init_sgtable(rq, &cmd->sdb);
>               return BLKPREP_OK;
>       }

Doesn't seem to be necessary for TYPE_ROM either..?

So requests of REQ_TYPE_BLOCK_PC for TYPE_ROM with scsi-mq are having
their sc->sdb.table setup from pre-allocated SGLs at the start of
scsi_mq_queue_rq(), before q->prep_rq_fn() -> sr_prep_fn() ->
scsi_setup_blk_pc_cmnd() is called.

--nab

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