This would be something for Jens to pick up.
Looks good to me,
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Next step would be to switch to the same default for all
implementations..
On Thu, Jun 05, 2014 at 10:02:22AM -0400, Douglas Gilbert wrote:
> After 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 on block layer device: blk_exec*(at_head=false)
> - sg device SG_IO: at_head=true
> - bsg device 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. A
> recent patch titled: "sg: add SG_FLAG_Q_AT_TAIL flag"
> allowed the sg driver default to be overridden. This patch
> allows a SG_IO ioctl sent to a block layer device to have
> its default overridden.
>
> ChangeLog:
> - introduce SG_FLAG_Q_AT_HEAD flag in sg.h to cause
> commands that are injected via a block layer
> device SG_IO ioctl to set at_head=true
> - make comments clearer about queueing in sg.h since the
> header is used both by the sg device and block layer
> device implementations of the SG_IO ioctl.
> - introduce BSG_FLAG_Q_AT_HEAD in bsg.h for compatibility
> (it does nothing) and update comments.
>
>
> Signed-off-by: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
> diff --git a/block/scsi_ioctl.c b/block/scsi_ioctl.c
> index 2648797..e49b7ef 100644
> --- a/block/scsi_ioctl.c
> +++ b/block/scsi_ioctl.c
> @@ -288,6 +288,7 @@ static int sg_io(struct request_queue *q, struct gendisk *bd_disk,
> unsigned long start_time;
> ssize_t ret = 0;
> int writing = 0;
> + int at_head = 0;
> struct request *rq;
> char sense[SCSI_SENSE_BUFFERSIZE];
> struct bio *bio;
> @@ -311,6 +312,8 @@ static int sg_io(struct request_queue *q, struct gendisk *bd_disk,
> case SG_DXFER_FROM_DEV:
> break;
> }
> + if (hdr->flags & SG_FLAG_Q_AT_HEAD)
> + at_head = 1;
>
> rq = blk_get_request(q, writing ? WRITE : READ, GFP_KERNEL);
> if (!rq)
> @@ -366,7 +369,7 @@ static int sg_io(struct request_queue *q, struct gendisk *bd_disk,
> * (if he doesn't check that is his problem).
> * N.B. a non-zero SCSI status is _not_ necessarily an error.
> */
> - blk_execute_rq(q, bd_disk, rq, 0);
> + blk_execute_rq(q, bd_disk, rq, at_head);
>
> hdr->duration = jiffies_to_msecs(jiffies - start_time);
>
> diff --git a/include/scsi/sg.h b/include/scsi/sg.h
> index 9859355..750e5db 100644
> --- a/include/scsi/sg.h
> +++ b/include/scsi/sg.h
> @@ -86,7 +86,9 @@ typedef struct sg_io_hdr
> #define SG_FLAG_MMAP_IO 4 /* request memory mapped IO */
> #define SG_FLAG_NO_DXFER 0x10000 /* no transfer of kernel buffers to/from */
> /* user space (debug indirect IO) */
> -#define SG_FLAG_Q_AT_TAIL 0x10 /* default is Q_AT_HEAD */
> +/* defaults:: for sg driver: Q_AT_HEAD; for block layer: Q_AT_TAIL */
> +#define SG_FLAG_Q_AT_TAIL 0x10
> +#define SG_FLAG_Q_AT_HEAD 0x20
>
> /* following 'info' values are "or"-ed together */
> #define SG_INFO_OK_MASK 0x1
> diff --git a/include/uapi/linux/bsg.h b/include/uapi/linux/bsg.h
> index 7a12e1c..02986cf 100644
> --- a/include/uapi/linux/bsg.h
> +++ b/include/uapi/linux/bsg.h
> @@ -10,12 +10,13 @@
> #define BSG_SUB_PROTOCOL_SCSI_TRANSPORT 2
>
> /*
> - * For flags member below
> - * sg.h sg_io_hdr also has bits defined for it's flags member. However
> - * none of these bits are implemented/used by bsg. The bits below are
> - * allocated to not conflict with sg.h ones anyway.
> + * For flag constants below:
> + * sg.h sg_io_hdr also has bits defined for it's flags member. These
> + * two flag values (0x10 and 0x20) have the same meaning in sg.h . For
> + * bsg the BSG_FLAG_Q_AT_HEAD flag is ignored since it is the deafult.
> */
> -#define BSG_FLAG_Q_AT_TAIL 0x10 /* default, == 0 at this bit, is Q_AT_HEAD */
> +#define BSG_FLAG_Q_AT_TAIL 0x10 /* default is Q_AT_HEAD */
> +#define BSG_FLAG_Q_AT_HEAD 0x20
>
> struct sg_io_v4 {
> __s32 guard; /* [i] 'Q' to differentiate from v3 */
---end quoted text---
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