bcachefs: improve "no device to read from" message

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/io_read.c

@@ -869,9 +869,15 @@ int __bch2_read_extent(struct btree_trans *trans, struct bch_read_bio *orig,
 		goto hole;
 
 	if (pick_ret < 0) {
+		struct printbuf buf = PRINTBUF;
+		bch2_bkey_val_to_text(&buf, c, k);
+
 		bch_err_inum_offset_ratelimited(c,
 				read_pos.inode, read_pos.offset << 9,
-				"no device to read from");
+				"no device to read from: %s\n  %s",
+				bch2_err_str(pick_ret),
+				buf.buf);
+		printbuf_exit(&buf);
 		goto err;
 	}