scst_vdisk: Port to Linux kernel v5.19

Support for the following block layer changes in the Linux Kernel v5.19:
- 44abff2c0b97 ("block: decouple REQ_OP_SECURE_ERASE from REQ_OP_DISCARD")
- 70200574cc22 ("block: remove QUEUE_FLAG_DISCARD")

scst/include/backport.h

@@ -206,6 +206,23 @@ void blk_execute_rq_nowait_backport(struct request *rq, bool at_head)
 #define blk_execute_rq_nowait blk_execute_rq_nowait_backport
 #endif
 
+/* <linux/blkdev.h> */
+
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 19, 0)
+/*
+ * See also commit 44abff2c0b97 ("block: decouple REQ_OP_SECURE_ERASE
+ * from REQ_OP_DISCARD") # v5.19.
+ */
+static inline
+int blkdev_issue_discard_backport(struct block_device *bdev, sector_t sector,
+		sector_t nr_sects, gfp_t gfp_mask)
+{
+	return blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask, 0);
+}
+
+#define blkdev_issue_discard blkdev_issue_discard_backport
+#endif
+
 /* <linux/byteorder/generic.h> */
 /*
  * See also f2f2efb807d3 ("byteorder: Move {cpu_to_be32, be32_to_cpu}_array()

scst/src/dev_handlers/scst_vdisk.c

@@ -562,8 +562,13 @@ static void vdisk_check_tp_support(struct scst_vdisk_dev *virt_dev)
 	fd_open = true;
 
 	if (virt_dev->blockio) {
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 19, 0)
+		virt_dev->dev_thin_provisioned =
+			!!bdev_max_discard_sectors(bdev);
+#else
 		virt_dev->dev_thin_provisioned =
 			blk_queue_discard(bdev_get_queue(bdev));
+#endif
 	} else {
 		virt_dev->dev_thin_provisioned = (fd->f_op->fallocate != NULL);
 	}
@@ -581,7 +586,6 @@ check:
 		if (virt_dev->thin_provisioned)
 			PRINT_INFO("Auto enable thin provisioning for device "
 				"%s", virt_dev->filename);
-
 	}
 
 	if (virt_dev->thin_provisioned) {
@@ -1811,8 +1815,7 @@ static int vdisk_unmap_range(struct scst_cmd *cmd,
 		sector_t nr_sects = blocks << (cmd->dev->block_shift - 9);
 		gfp_t gfp = cmd->cmd_gfp_mask;
 
-		err = blkdev_issue_discard(bdev, start_sector, nr_sects, gfp,
-					   0);
+		err = blkdev_issue_discard(bdev, start_sector, nr_sects, gfp);
 		if (unlikely(err != 0)) {
 			PRINT_ERROR("blkdev_issue_discard() for "
 				"LBA %lld, blocks %lld failed: %d",