nfsd: don't advertise a SCSI layout for an unsupported request_queue

Commit 30181faa ("nfsd: Check queue type before submitting a SCSI
request") did the work of ensuring that we don't send SCSI requests to a
request queue that won't support them, but that check is in the
GETDEVICEINFO path.  Let's not set the SCSI layout in fs_layout_type in the
first place, and then we'll have less clients sending GETDEVICEINFO for
non-SCSI request queues and less unnecessary WARN_ONs.

While we're in here, remove some outdated comments that refer to
"overwriting" layout seletion because commit 8a4c3926 ("nfsd: allow
nfsd to advertise multiple layout types") changed things to no longer
overwrite the layout type.
Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4layouts.c

@@ -133,27 +133,20 @@ void nfsd4_setup_layout_type(struct svc_export *exp)
 	if (!(exp->ex_flags & NFSEXP_PNFS))
 		return;
 
-	/*
-	 * If flex file is configured, use it by default. Otherwise
-	 * check if the file system supports exporting a block-like layout.
-	 * If the block device supports reservations prefer the SCSI layout,
-	 * otherwise advertise the block layout.
-	 */
 #ifdef CONFIG_NFSD_FLEXFILELAYOUT
 	exp->ex_layout_types |= 1 << LAYOUT_FLEX_FILES;
 #endif
 #ifdef CONFIG_NFSD_BLOCKLAYOUT
-	/* overwrite flex file layout selection if needed */
 	if (sb->s_export_op->get_uuid &&
 	    sb->s_export_op->map_blocks &&
 	    sb->s_export_op->commit_blocks)
 		exp->ex_layout_types |= 1 << LAYOUT_BLOCK_VOLUME;
 #endif
 #ifdef CONFIG_NFSD_SCSILAYOUT
-	/* overwrite block layout selection if needed */
 	if (sb->s_export_op->map_blocks &&
 	    sb->s_export_op->commit_blocks &&
-	    sb->s_bdev && sb->s_bdev->bd_disk->fops->pr_ops)
+	    sb->s_bdev && sb->s_bdev->bd_disk->fops->pr_ops &&
+		blk_queue_scsi_passthrough(sb->s_bdev->bd_disk->queue))
 		exp->ex_layout_types |= 1 << LAYOUT_SCSI;
 #endif
 }