bdev: add getter for write cache enable status

Change-Id: I93656deda8956c77e9565ee1f271795642e62ac9
Signed-off-by: Daniel Verkamp <daniel.verkamp@intel.com>

include/spdk/bdev.h

@@ -249,6 +249,17 @@ uint32_t spdk_bdev_get_max_unmap_descriptors(const struct spdk_bdev *bdev);
  */
 size_t spdk_bdev_get_buf_align(const struct spdk_bdev *bdev);
 
+/**
+ * Query whether block device has an enabled write cache.
+ *
+ * \param bdev Block device to query.
+ * \return true if block device has a volatile write cache enabled.
+ *
+ * If this function returns true, written data may not be persistent until a flush command
+ * is issued.
+ */
+bool spdk_bdev_has_write_cache(const struct spdk_bdev *bdev);
+
 struct spdk_bdev_io *spdk_bdev_read(struct spdk_bdev *bdev, struct spdk_io_channel *ch,
 				    void *buf, uint64_t offset, uint64_t nbytes,
 				    spdk_bdev_io_completion_cb cb, void *cb_arg);

lib/bdev/bdev.c

@@ -574,6 +574,12 @@ spdk_bdev_get_buf_align(const struct spdk_bdev *bdev)
 	return 1;
 }
 
+bool
+spdk_bdev_has_write_cache(const struct spdk_bdev *bdev)
+{
+	return bdev->write_cache;
+}
+
 static int
 spdk_bdev_io_valid(struct spdk_bdev *bdev, uint64_t offset, uint64_t nbytes)
 {

lib/scsi/scsi_bdev.c

@@ -888,7 +888,7 @@ spdk_bdev_scsi_mode_sense_page(struct spdk_bdev *bdev,
 		plen = 0x12 + 2;
 		mode_sense_page_init(cp, plen, page, subpage);
 
-		if (cp && bdev->write_cache && pc != 0x01)
+		if (cp && spdk_bdev_has_write_cache(bdev) && pc != 0x01)
 			cp[2] |= 0x4; /* WCE */
 
 		/* Read Cache Disable (RCD) = 1 */

test/lib/scsi/scsi_bdev/scsi_bdev_ut.c

@@ -115,6 +115,12 @@ spdk_bdev_get_max_unmap_descriptors(const struct spdk_bdev *bdev)
 	return 1;
 }
 
+bool
+spdk_bdev_has_write_cache(const struct spdk_bdev *bdev)
+{
+	return false;
+}
+
 void
 spdk_scsi_lun_clear_all(struct spdk_scsi_lun *lun)
 {