block: remove QUEUE_FLAG_DISCARD

Just use a non-zero max_discard_sectors as an indicator for discard
support, similar to what is done for write zeroes.

The only places where needs special attention is the RAID5 driver,
which must clear discard support for security reasons by default,
even if the default stacking rules would allow for it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Acked-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com> [drbd]
Acked-by: Jan Höppner <hoeppner@linux.ibm.com> [s390]
Acked-by: Coly Li <colyli@suse.de> [bcache]
Acked-by: David Sterba <dsterba@suse.com> [btrfs]
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20220415045258.199825-25-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk-core.c b/block/blk-core.c
index 937bb6b..b5c3a80 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -820,7 +820,7 @@ void submit_bio_noacct(struct bio *bio)
 
 	switch (bio_op(bio)) {
 	case REQ_OP_DISCARD:
-		if (!blk_queue_discard(q))
+		if (!bdev_max_discard_sectors(bdev))
 			goto not_supported;
 		break;
 	case REQ_OP_SECURE_ERASE:
diff --git a/block/blk-lib.c b/block/blk-lib.c
index 2ae32a7..8b4b66d 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -53,7 +53,7 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
 			return -EOPNOTSUPP;
 		op = REQ_OP_SECURE_ERASE;
 	} else {
-		if (!blk_queue_discard(q))
+		if (!bdev_max_discard_sectors(bdev))
 			return -EOPNOTSUPP;
 		op = REQ_OP_DISCARD;
 	}
diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index aa0349e..fd111c5 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -113,7 +113,6 @@ static const char *const blk_queue_flag_name[] = {
 	QUEUE_FLAG_NAME(FAIL_IO),
 	QUEUE_FLAG_NAME(NONROT),
 	QUEUE_FLAG_NAME(IO_STAT),
-	QUEUE_FLAG_NAME(DISCARD),
 	QUEUE_FLAG_NAME(NOXMERGES),
 	QUEUE_FLAG_NAME(ADD_RANDOM),
 	QUEUE_FLAG_NAME(SECERASE),
diff --git a/block/ioctl.c b/block/ioctl.c
index 19c32b7..eaee0ef 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -87,14 +87,13 @@ static int blk_ioctl_discard(struct block_device *bdev, fmode_t mode,
 {
 	uint64_t range[2];
 	uint64_t start, len;
-	struct request_queue *q = bdev_get_queue(bdev);
 	struct inode *inode = bdev->bd_inode;
 	int err;
 
 	if (!(mode & FMODE_WRITE))
 		return -EBADF;
 
-	if (!blk_queue_discard(q))
+	if (!bdev_max_discard_sectors(bdev))
 		return -EOPNOTSUPP;
 
 	if (copy_from_user(range, (void __user *)arg, sizeof(range)))