[PATCH v13 44/45] sg: [RFC] add blk_poll support

[Douglas Gilbert <dgilbert@interlog.com>]

The support is added via the new SGV4_FLAG_HIPRI command flag which
causes REQ_HIPRI to be set on the request. Before waiting on an
inflight request, it is checked to see if it has SGV4_FLAG_HIPRI,
and if so blk_poll() is called instead of the wait. In situations
where only the file descriptor is known (e.g. sg_poll() and
ioctl(SG_GET_NUM_WAITING)) all inflight requests associated with
the file descriptor that have SGV4_FLAG_HIPRI set, have sg_poll()
called on them.

Note that the implementation of blk_poll() calls mq_poll() in the
LLD associated with the request. Then for any request found to be
ready, blk_poll() invokes the scsi_done() callback. So this means
if blk_poll() returns 1 then sg_rq_end_io() has already been
called for the polled request.

Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
---
 drivers/scsi/sg.c      | 87 ++++++++++++++++++++++++++++++++++++++++--
 include/uapi/scsi/sg.h |  1 +
 2 files changed, 84 insertions(+), 4 deletions(-)

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index ad97f0756a9c..b396d3fb7bb7 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -123,6 +123,7 @@ enum sg_rq_state {	/* N.B. sg_rq_state_arr assumes SG_RS_AWAIT_RCV==2 */
 #define SG_FFD_CMD_Q		1	/* clear: only 1 active req per fd */
 #define SG_FFD_KEEP_ORPHAN	2	/* policy for this fd */
 #define SG_FFD_MMAP_CALLED	3	/* mmap(2) system call made on fd */
+#define SG_FFD_HIPRI_SEEN	4	/* could have HIPRI requests active */
 #define SG_FFD_Q_AT_TAIL	5	/* set: queue reqs at tail of blk q */
 
 /* Bit positions (flags) for sg_device::fdev_bm bitmask follow */
@@ -301,6 +302,8 @@ static struct sg_device *sg_get_dev(int min_dev);
 static void sg_device_destroy(struct kref *kref);
 static struct sg_request *sg_mk_srp_sgat(struct sg_fd *sfp, bool first,
 					 int db_len);
+static int sg_sfp_blk_poll(struct sg_fd *sfp, int loop_count);
+static int sg_srp_blk_poll(struct sg_request *srp, int loop_count);
 #if IS_ENABLED(CONFIG_SCSI_LOGGING) && IS_ENABLED(SG_DEBUG)
 static const char *sg_rq_st_str(enum sg_rq_state rq_st, bool long_str);
 #endif
@@ -1033,6 +1036,8 @@ sg_execute_cmd(struct sg_fd *sfp, struct sg_request *srp)
 		atomic_inc(&sfp->submitted);
 		set_bit(SG_FRQ_COUNT_ACTIVE, srp->frq_bm);
 	}
+	if (srp->rq_flags & SGV4_FLAG_HIPRI)
+		srp->rq->cmd_flags |= REQ_HIPRI;
 	blk_execute_rq_nowait(sdp->device->request_queue, sdp->disk,
 			      srp->rq, (int)at_head, sg_rq_end_io);
 }
@@ -1705,6 +1710,12 @@ sg_wait_event_srp(struct file *filp, struct sg_fd *sfp, void __user *p,
 
 	if (atomic_read(&srp->rq_st) != SG_RS_INFLIGHT)
 		goto skip_wait;		/* and skip _acquire() */
+	if (srp->rq_flags & SGV4_FLAG_HIPRI) {
+		res = sg_srp_blk_poll(srp, -1);	/* spin till found */
+		if (unlikely(res < 0))
+			return res;
+		goto skip_wait;
+	}
 	SG_LOG(3, sfp, "%s: about to wait_event...()\n", __func__);
 	/* usually will be woken up by sg_rq_end_io() callback */
 	res = wait_event_interruptible(sfp->read_wait,
@@ -2032,6 +2043,8 @@ sg_ioctl_common(struct file *filp, struct sg_device *sdp, struct sg_fd *sfp,
 		SG_LOG(3, sfp, "%s:    SG_GET_PACK_ID=%d\n", __func__, val);
 		return put_user(val, ip);
 	case SG_GET_NUM_WAITING:
+		if (test_bit(SG_FFD_HIPRI_SEEN, sfp->ffd_bm))
+			sg_sfp_blk_poll(sfp, 0);	/* LLD may have some ready push */
 		val = atomic_read(&sfp->waiting);
 		if (val)
 			return put_user(val, ip);
@@ -2241,6 +2254,59 @@ sg_compat_ioctl(struct file *filp, unsigned int cmd_in, unsigned long arg)
 }
 #endif
 
+static int
+sg_srp_q_blk_poll(struct sg_request *srp, struct request_queue *q, int loop_count)
+{
+	int k, n, num;
+	blk_qc_t cookie = request_to_qc_t(srp->rq->mq_hctx, srp->rq);
+
+	num = (loop_count < 1) ? 1 : loop_count;
+	for (k = 0; k < num; ++k) {
+		n = blk_poll(q, cookie, loop_count < 0 /* spin if negative */);
+		if (n != 0)
+			return n;
+	}
+	return 0;
+}
+
+/*
+ * Check all requests on this sfp that are both inflight and HIPRI. That check involves calling
+ * blk_poll(spin<-false) loop_count times. If loop_count is 0 then call blk_poll once.
+ * If loop_count is negative then call blk_poll(spin<-true)) once for each request.
+ * Returns number found (could be 0) or a negated errno value.
+ */
+static int
+sg_sfp_blk_poll(struct sg_fd *sfp, int loop_count)
+{
+	int res = 0;
+	int n;
+	unsigned long idx;
+	struct sg_request *srp;
+	struct scsi_device *sdev = sfp->parentdp->device;
+	struct request_queue *q = sdev ? sdev->request_queue : NULL;
+	struct xarray *xafp = &sfp->srp_arr;
+
+	if (!q)
+		return -EINVAL;
+	xa_for_each(xafp, idx, srp) {
+		if (atomic_read(&srp->rq_st) != SG_RS_INFLIGHT)
+			continue;
+		if (!(srp->rq_flags & SGV4_FLAG_HIPRI))
+			continue;
+		n = sg_srp_q_blk_poll(srp, q, loop_count);
+		if (unlikely(n < 0))
+			return n;
+		res += n;
+	}
+	return res;
+}
+
+static inline int
+sg_srp_blk_poll(struct sg_request *srp, int loop_count)
+{
+	return sg_srp_q_blk_poll(srp, srp->parentfp->parentdp->device->request_queue, loop_count);
+}
+
 /*
  * Implements the poll(2) system call for this driver. Returns various EPOLL*
  * flags OR-ed together.
@@ -2252,6 +2318,8 @@ sg_poll(struct file *filp, poll_table * wait)
 	__poll_t p_res = 0;
 	struct sg_fd *sfp = filp->private_data;
 
+	if (test_bit(SG_FFD_HIPRI_SEEN, sfp->ffd_bm))
+		sg_sfp_blk_poll(sfp, 0);	/* LLD may have some ready to push up */
 	num = atomic_read(&sfp->waiting);
 	if (num < 1) {
 		poll_wait(filp, &sfp->read_wait, wait);
@@ -2564,7 +2632,8 @@ sg_rq_end_io(struct request *rq, blk_status_t status)
 
 	if (likely(rqq_state == SG_RS_AWAIT_RCV)) {
 		/* Wake any sg_read()/ioctl(SG_IORECEIVE) awaiting this req */
-		wake_up_interruptible(&sfp->read_wait);
+		if (!(srp->rq_flags & SGV4_FLAG_HIPRI))
+			wake_up_interruptible(&sfp->read_wait);
 		kill_fasync(&sfp->async_qp, SIGPOLL, POLL_IN);
 		kref_put(&sfp->f_ref, sg_remove_sfp);
 	} else {        /* clean up orphaned request that aren't being kept */
@@ -3007,6 +3076,10 @@ sg_start_req(struct sg_request *srp, struct sg_comm_wr_t *cwrp, int dxfer_dir)
 	/* current sg_request protected by SG_RS_BUSY state */
 	scsi_rp = scsi_req(rq);
 	srp->rq = rq;
+	if (rq_flags & SGV4_FLAG_HIPRI) {
+		if (!test_bit(SG_FFD_HIPRI_SEEN, sfp->ffd_bm))
+			set_bit(SG_FFD_HIPRI_SEEN, sfp->ffd_bm);
+	}
 
 	if (cwrp->cmd_len > BLK_MAX_CDB)
 		scsi_rp->cmd = long_cmdp;
@@ -3120,7 +3193,10 @@ sg_finish_scsi_blk_rq(struct sg_request *srp)
 	SG_LOG(4, sfp, "%s: srp=0x%pK%s\n", __func__, srp,
 	       (srp->parentfp->rsv_srp == srp) ? " rsv" : "");
 	if (test_and_clear_bit(SG_FRQ_COUNT_ACTIVE, srp->frq_bm)) {
-		atomic_dec(&sfp->submitted);
+		bool now_zero = !atomic_dec_and_test(&sfp->submitted);
+
+		if (now_zero && test_bit(SG_FFD_HIPRI_SEEN, sfp->ffd_bm))
+			clear_bit(SG_FFD_HIPRI_SEEN, sfp->ffd_bm);
 		atomic_dec(&sfp->waiting);
 	}
 
@@ -3321,6 +3397,8 @@ sg_find_srp_by_id(struct sg_fd *sfp, int pack_id)
 	struct sg_request *srp = NULL;
 	struct xarray *xafp = &sfp->srp_arr;
 
+	if (test_bit(SG_FFD_HIPRI_SEEN, sfp->ffd_bm))
+		sg_sfp_blk_poll(sfp, 0);	/* LLD may have some ready to push up */
 	if (num_waiting < 1) {
 		num_waiting = atomic_read_acquire(&sfp->waiting);
 		if (num_waiting < 1)
@@ -4127,8 +4205,9 @@ sg_proc_debug_sreq(struct sg_request *srp, int to, char *obp, int len)
 	else if (dur < U32_MAX)	/* in-flight or busy (so ongoing) */
 		n += scnprintf(obp + n, len - n, " t_o/elap=%us/%ums",
 			       to / 1000, dur);
-	n += scnprintf(obp + n, len - n, " sgat=%d op=0x%02x\n",
-		       srp->sgat_h.num_sgat, srp->cmd_opcode);
+	cp = (srp->rq_flags & SGV4_FLAG_HIPRI) ? "hipri " : "";
+	n += scnprintf(obp + n, len - n, " sgat=%d %sop=0x%02x\n",
+		       srp->sgat_h.num_sgat, cp, srp->cmd_opcode);
 	return n;
 }
 
diff --git a/include/uapi/scsi/sg.h b/include/uapi/scsi/sg.h
index cbade2870355..a0e11d87aa2e 100644
--- a/include/uapi/scsi/sg.h
+++ b/include/uapi/scsi/sg.h
@@ -110,6 +110,7 @@ typedef struct sg_io_hdr {
 #define SGV4_FLAG_Q_AT_TAIL SG_FLAG_Q_AT_TAIL
 #define SGV4_FLAG_Q_AT_HEAD SG_FLAG_Q_AT_HEAD
 #define SGV4_FLAG_IMMED 0x400 /* for polling with SG_IOR, ignored in SG_IOS */
+#define SGV4_FLAG_HIPRI 0x800 /* request will use blk_poll to complete */
 
 /* Output (potentially OR-ed together) in v3::info or v4::info field */
 #define SG_INFO_OK_MASK 0x1
-- 
2.25.1