On Sun, Mar 30, 2014 at 10:45:04PM -0700, Nicholas A. Bellinger wrote:
> > int scsi_setup_blk_pc_cmnd(struct scsi_device *sdev, struct request *req)
> > {
> > - struct scsi_cmnd *cmd;
> > - int ret = scsi_prep_state_check(sdev, req);
> > -
> > - if (ret != BLKPREP_OK)
> > - return ret;
> > -
> > - cmd = scsi_get_cmd_from_req(sdev, req);
> > - if (unlikely(!cmd))
> > - return BLKPREP_DEFER;
> > + struct scsi_cmnd *cmd = req->special;
> >
>
> Mmm, I thought that req->special was only holding a pointer to a
> pre-allocated scsi_cmnd during mq operation, no..?
For the mq case the block layer sets up req->special. For the old case
scsi_get_cmd_from_req sets up req->special the first it is called, and
leaves it in there until the command is done.
> > + ret = scsi_prep_state_check(sdev, req);
> > + if (ret != BLKPREP_OK)
> > + goto out;
> > +
> > + cmd = scsi_get_cmd_from_req(sdev, req);
> > + if (unlikely(!cmd)) {
> > + ret = BLKPREP_DEFER;
> > + goto out;
> > + }
> > +
>From here the req->special pointer may or may not be set depending on mq
operation, no..?
a) there is no blk-mq support yet in James tree (+ these patches)
b) even in my scsi-mq tree this code path won't be called for the mq case
c) after scsi_get_cmd_from_req returns req->special will always be set up
to point to the scsi_cmnd:
static struct scsi_cmnd *scsi_get_cmd_from_req(struct scsi_device *sdev,
struct request *req)
{
struct scsi_cmnd *cmd;
if (!req->special) {
...
req->special = cmd;
} else {
cmd = req->special;
}
/* pull a tag out of the request if we have one */
cmd->tag = req->tag;
cmd->request = req;
cmd->cmnd = req->cmd;
cmd->prot_op = SCSI_PROT_NORMAL;
return cmd;
}
> > }
> > ret = scsi_setup_fs_cmnd(sdp, rq);
> > if (ret != BLKPREP_OK)
>
> And this currently assumes req->special is always set when calling
> scsi_setup_fs_cmnd()
That is the case both before and after this patch.
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