#endif
}
+/*
+ * Detect if a device has a write cache. Used to set the intial value for the
+ * vdev nowritecache flag.
+ *
+ * 4.10: QUEUE_FLAG_WC added. Initialised by the driver, but can be changed
+ * later by the operator. If not set, kernel will return flush requests
+ * immediately without doing anything.
+ * 6.6: QUEUE_FLAG_HW_WC added. Initialised by the driver, can't be changed.
+ * Only controls if the operator is allowed to change _WC. Initial version
+ * buggy; aliased to QUEUE_FLAG_FUA, so unuseable.
+ * 6.6.10, 6.7: QUEUE_FLAG_HW_WC fixed.
+ *
+ * Older than 4.10 we just assume write cache, and let the normal flush fail
+ * detection apply.
+ */
+static inline boolean_t
+zfs_bdev_has_write_cache(struct block_device *bdev)
+{
+#if defined(QUEUE_FLAG_HW_WC) && QUEUE_FLAG_HW_WC != QUEUE_FLAG_FUA
+ return (test_bit(QUEUE_FLAG_HW_WC, &bdev_get_queue(bdev)->queue_flags));
+#elif defined(QUEUE_FLAG_WC)
+ return (test_bit(QUEUE_FLAG_WC, &bdev_get_queue(bdev)->queue_flags));
+#else
+ return (B_TRUE);
+#endif
+}
+
static inline void
blk_queue_set_read_ahead(struct request_queue *q, unsigned long ra_pages)
{
/* Determine the logical block size */
int logical_block_size = bdev_logical_block_size(bdev);
- /* Clear the nowritecache bit, causes vdev_reopen() to try again. */
- v->vdev_nowritecache = B_FALSE;
+ /*
+ * If the device has a write cache, clear the nowritecache flag,
+ * so that we start issuing flush requests again.
+ */
+ v->vdev_nowritecache = !zfs_bdev_has_write_cache(bdev);
/* Set when device reports it supports TRIM. */
v->vdev_has_trim = bdev_discard_supported(bdev);