Try to derive the qcow2 file format from an image file automatically.

This makes the "-d qcow2:" and "format qcow" arguments optional as vmctl
and vmd will read the magic bytes at the beginning of a file to guess if
it is a raw or a qcow image file.

The "vmctl create" command has been changed by removing the -f qcow2 option
and replacing it with the same syntax as -d: "vmctl create qcow2:foo.img".
In a slightly ununixy but intended way, the create command now also
considers the file extension for the format as "vmctl create foo.qcow2"
creates a qcow2 disk and not a raw image file.

Ok mlarkin@ (and ccardenas@ on an earlier version of the diff)

1 files changed, 3 insertions, 2 deletions

diff --git a/usr.sbin/vmd/vioqcow2.c b/usr.sbin/vmd/vioqcow2.c
index ada0bafc72d..ceb95fe37c4 100644
--- a/usr.sbin/vmd/vioqcow2.c
+++ b/usr.sbin/vmd/vioqcow2.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: vioqcow2.c,v 1.5 2018/09/28 12:35:32 reyk Exp $	*/
+/*	$OpenBSD: vioqcow2.c,v 1.6 2018/10/01 09:31:15 reyk Exp $	*/
 
 /*
  * Copyright (c) 2018 Ori Bernstein <ori@eigenstate.org>
@@ -169,7 +169,8 @@ qc2_open(struct qcdisk *disk, int fd)
 		log_warn("%s: short read on header", __func__);
 		goto error;
 	}
-	if (strncmp(header.magic, "QFI\xfb", 4) != 0) {
+	if (strncmp(header.magic,
+	    VM_MAGIC_QCOW, strlen(VM_MAGIC_QCOW)) != 0) {
 		log_warn("%s: invalid magic numbers", __func__);
 		goto error;
 	}