This would be something for Jens to pick up. Looks good to me,
Reviewed-by: Christoph Hellwig <[email protected]> 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 <[email protected]> > 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--- -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
