[PATCH 14/14] block: add special APIs for run-time disabling of discard and friends

[Christoph Hellwig <hch@lst.de>]

A few drivers optimistically try to support discard, write zeroes and
secure erase and disable the features from the I/O completion handler
if the hardware can't support them.  This disable can't be done using
the atomic queue limits API because the I/O completion handlers can't
take sleeping locks or freeze the queue.  Keep the existing clearing
of the relevant field to zero, but replace the old blk_queue_max_*
APIs with new disable APIs that force the value to 0.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
---
 arch/um/drivers/ubd_kern.c   |  4 ++--
 block/blk-settings.c         | 41 ------------------------------------
 drivers/block/xen-blkfront.c |  4 ++--
 drivers/scsi/sd.c            |  4 ++--
 include/linux/blkdev.h       | 28 ++++++++++++++++++------
 5 files changed, 28 insertions(+), 53 deletions(-)

diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
index 093c87879d08ba..cdcb75a68989dd 100644
--- a/arch/um/drivers/ubd_kern.c
+++ b/arch/um/drivers/ubd_kern.c
@@ -451,9 +451,9 @@ static void ubd_end_request(struct io_thread_req *io_req)
 {
 	if (io_req->error == BLK_STS_NOTSUPP) {
 		if (req_op(io_req->req) == REQ_OP_DISCARD)
-			blk_queue_max_discard_sectors(io_req->req->q, 0);
+			blk_queue_disable_discard(io_req->req->q);
 		else if (req_op(io_req->req) == REQ_OP_WRITE_ZEROES)
-			blk_queue_max_write_zeroes_sectors(io_req->req->q, 0);
+			blk_queue_disable_write_zeroes(io_req->req->q);
 	}
 	blk_mq_end_request(io_req->req, io_req->error);
 	kfree(io_req);
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 0b038729608f4b..996f247fc98e80 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -293,47 +293,6 @@ int queue_limits_set(struct request_queue *q, struct queue_limits *lim)
 }
 EXPORT_SYMBOL_GPL(queue_limits_set);
 
-/**
- * blk_queue_max_discard_sectors - set max sectors for a single discard
- * @q:  the request queue for the device
- * @max_discard_sectors: maximum number of sectors to discard
- **/
-void blk_queue_max_discard_sectors(struct request_queue *q,
-		unsigned int max_discard_sectors)
-{
-	struct queue_limits *lim = &q->limits;
-
-	lim->max_hw_discard_sectors = max_discard_sectors;
-	lim->max_discard_sectors =
-		min(max_discard_sectors, lim->max_user_discard_sectors);
-}
-EXPORT_SYMBOL(blk_queue_max_discard_sectors);
-
-/**
- * blk_queue_max_secure_erase_sectors - set max sectors for a secure erase
- * @q:  the request queue for the device
- * @max_sectors: maximum number of sectors to secure_erase
- **/
-void blk_queue_max_secure_erase_sectors(struct request_queue *q,
-		unsigned int max_sectors)
-{
-	q->limits.max_secure_erase_sectors = max_sectors;
-}
-EXPORT_SYMBOL(blk_queue_max_secure_erase_sectors);
-
-/**
- * blk_queue_max_write_zeroes_sectors - set max sectors for a single
- *                                      write zeroes
- * @q:  the request queue for the device
- * @max_write_zeroes_sectors: maximum number of sectors to write per command
- **/
-void blk_queue_max_write_zeroes_sectors(struct request_queue *q,
-		unsigned int max_write_zeroes_sectors)
-{
-	q->limits.max_write_zeroes_sectors = max_write_zeroes_sectors;
-}
-EXPORT_SYMBOL(blk_queue_max_write_zeroes_sectors);
-
 void disk_update_readahead(struct gendisk *disk)
 {
 	blk_apply_bdi_limits(disk->bdi, &disk->queue->limits);
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index fd7c0ff2139cee..9b4ec3e4908cce 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -1605,8 +1605,8 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
 				blkif_req(req)->error = BLK_STS_NOTSUPP;
 				info->feature_discard = 0;
 				info->feature_secdiscard = 0;
-				blk_queue_max_discard_sectors(rq, 0);
-				blk_queue_max_secure_erase_sectors(rq, 0);
+				blk_queue_disable_discard(rq);
+				blk_queue_disable_secure_erase(rq);
 			}
 			break;
 		case BLKIF_OP_FLUSH_DISKCACHE:
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 049071b5681989..d957e29b17a98a 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -837,7 +837,7 @@ static unsigned char sd_setup_protect_cmnd(struct scsi_cmnd *scmd,
 static void sd_disable_discard(struct scsi_disk *sdkp)
 {
 	sdkp->provisioning_mode = SD_LBP_DISABLE;
-	blk_queue_max_discard_sectors(sdkp->disk->queue, 0);
+	blk_queue_disable_discard(sdkp->disk->queue);
 }
 
 static void sd_config_discard(struct scsi_disk *sdkp, struct queue_limits *lim,
@@ -1019,7 +1019,7 @@ static void sd_disable_write_same(struct scsi_disk *sdkp)
 {
 	sdkp->device->no_write_same = 1;
 	sdkp->max_ws_blocks = 0;
-	blk_queue_max_write_zeroes_sectors(sdkp->disk->queue, 0);
+	blk_queue_disable_write_zeroes(sdkp->disk->queue);
 }
 
 static void sd_config_write_same(struct scsi_disk *sdkp,
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index ad995e7a769811..ac8e0cb2353a0e 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -912,15 +912,31 @@ static inline void queue_limits_cancel_update(struct request_queue *q)
 	mutex_unlock(&q->limits_lock);
 }
 
+/*
+ * These helpers are for drivers that have sloppy feature negotiation and might
+ * have to disable DISCARD, WRITE_ZEROES or SECURE_DISCARD from the I/O
+ * completion handler when the device returned an indicator that the respective
+ * feature is not actually supported.  They are racy and the driver needs to
+ * cope with that.  Try to avoid this scheme if you can.
+ */
+static inline void blk_queue_disable_discard(struct request_queue *q)
+{
+	q->limits.max_discard_sectors = 0;
+}
+
+static inline void blk_queue_disable_secure_erase(struct request_queue *q)
+{
+	q->limits.max_secure_erase_sectors = 0;
+}
+
+static inline void blk_queue_disable_write_zeroes(struct request_queue *q)
+{
+	q->limits.max_write_zeroes_sectors = 0;
+}
+
 /*
  * Access functions for manipulating queue properties
  */
-void blk_queue_max_secure_erase_sectors(struct request_queue *q,
-		unsigned int max_sectors);
-extern void blk_queue_max_discard_sectors(struct request_queue *q,
-		unsigned int max_discard_sectors);
-extern void blk_queue_max_write_zeroes_sectors(struct request_queue *q,
-		unsigned int max_write_same_sectors);
 void disk_update_readahead(struct gendisk *disk);
 extern void blk_limits_io_min(struct queue_limits *limits, unsigned int min);
 extern void blk_limits_io_opt(struct queue_limits *limits, unsigned int opt);
-- 
2.43.0