From d15156138dad40205c9fdd9abe85c9e1479ae272 Mon Sep 17 00:00:00 2001 From: Douglas Gilbert Date: Tue, 1 Jul 2014 10:48:05 -0600 Subject: [PATCH] block SG_IO: add SG_FLAG_Q_AT_HEAD flag 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 Reviewed-by: Christoph Hellwig Reviewed-by: Mike Christie Signed-off-by: Jens Axboe --- block/scsi_ioctl.c | 5 ++++- include/scsi/sg.h | 3 +++ include/uapi/linux/bsg.h | 11 ++++++----- 3 files changed, 13 insertions(+), 6 deletions(-) diff --git a/block/scsi_ioctl.c b/block/scsi_ioctl.c index bda1497add4c..51bf5155ee75 100644 --- a/block/scsi_ioctl.c +++ b/block/scsi_ioctl.c @@ -290,6 +290,7 @@ 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; @@ -313,6 +314,8 @@ 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) @@ -369,7 +372,7 @@ 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 a9f3c6fc3f57..4734c15ab5d6 100644 --- a/include/scsi/sg.h +++ b/include/scsi/sg.h @@ -129,6 +129,9 @@ 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) */ +/* 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 7a12e1c0f371..02986cf8b6f1 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 */ -- 2.20.1