On Tue, Jun 03, 2014 at 09:36:56PM -0400, Douglas Gilbert wrote:
> When the SG_IO ioctl was copied into the block layer and
> later into the bsg driver, subtle differences emerged.
>
> One difference is the way injected commands are queued through
> the block layer (i.e. this is not SCSI device queueing nor SATA
> NCQ). Summarizing:
> - SG_IO in the block layer: blk_exec*(at_head=false)
> - sg SG_IO: at_head=true
> - bsg SG_IO: at_head=true
>
> Some time ago Boaz Harrosh introduced a sg v4 flag called
> BSG_FLAG_Q_AT_TAIL to override the bsg driver default.
> This patch does the equivalent for the sg driver.
>
> ChangeLog:
> Introduce SG_FLAG_Q_AT_TAIL flag to cause commands
> to be injected into the block layer with
> at_head=false.
>
> Signed-off-by: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
> index 177f755..1b7d4f6 100644
> --- a/drivers/scsi/sg.c
> +++ b/drivers/scsi/sg.c
> @@ -740,7 +740,7 @@ static int
> sg_common_write(Sg_fd * sfp, Sg_request * srp,
> unsigned char *cmnd, int timeout, int blocking)
> {
> - int k, data_dir;
> + int k, data_dir, at_head;
> Sg_device *sdp = sfp->parentdp;
> sg_io_hdr_t *hp = &srp->header;
>
> @@ -784,11 +784,12 @@ sg_common_write(Sg_fd * sfp, Sg_request * srp,
> break;
> }
> hp->duration = jiffies_to_msecs(jiffies);
> + at_head = !(hp->interface_id && (SG_FLAG_Q_AT_TAIL & hp->flags));
It seems like all other occurances of ->interface_id compare to either
'\0' or 'S', so this looks odd. Also I think this would really benefit
from beeing untangled into and if/else as it took me literally two
minutes to parse..
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