buildextend-live: add --miniso switch

This switch enables the new minimal ISO packing feature (see
coreos/coreos-installer#559).

Once a coreos-installer version with miniso support is present in RHCOS
and FCOS, we can make it unconditional and drop the switch. For now,
this will allow testing in the coreos-installer upstream CI.

src/cmd-buildextend-live

@@ -51,6 +51,8 @@ parser.add_argument("--fast", action='store_true', default=False,
                     help="Reduce compression for development (FCOS only)")
 parser.add_argument("--force", action='store_true', default=False,
                     help="Overwrite previously generated installer")
+parser.add_argument("--miniso", action='store_true', default=False,
+                    help="Enable minimal ISO packing (temporary)")
 args = parser.parse_args()
 
 # Identify the builds and target the latest build if none provided
@@ -120,6 +122,9 @@ for d in (tmpdir, tmpisoroot, tmpisocoreos, tmpisoimages, tmpisoimagespxe,
 # Size of file used to embed an Ignition config within a CPIO.
 ignition_img_size = 256 * 1024
 
+# Size of the file used to embed miniso data.
+miniso_data_file_size = 16 * 1024
+
 
 # The kernel requires that uncompressed cpio archives appended to an initrd
 # start on a 4-byte boundary.  If there's misalignment, it stops unpacking
@@ -581,15 +586,28 @@ boot
             fh.write('\n')
 
     # Define inputs and outputs
-    genisoargs += ['-o', tmpisofile, tmpisoroot]
+    genisoargs_final = genisoargs + ['-o', tmpisofile, tmpisoroot]
+
+    if args.miniso:
+        miniso_data = os.path.join(tmpisocoreos, "miniso.dat")
+        with open(miniso_data, 'wb') as f:
+            f.truncate(miniso_data_file_size)
 
-    run_verbose(genisoargs)
+    run_verbose(genisoargs_final)
 
     # Add MBR, and GPT with ESP, for x86_64 BIOS/UEFI boot when ISO is
     # copied to a USB stick
     if basearch == "x86_64":
         run_verbose(['/usr/bin/isohybrid', '--uefi', tmpisofile])
 
+    if args.miniso:
+        genisoargs_minimal = genisoargs + ['-o', f'{tmpisofile}.minimal', tmpisoroot]
+        os.unlink(iso_rootfs)
+        os.unlink(miniso_data)
+        run_verbose(genisoargs_minimal)
+        if basearch == "x86_64":
+            run_verbose(['/usr/bin/isohybrid', '--uefi', f'{tmpisofile}.minimal'])
+
     isoinfo = run_verbose(['isoinfo', '-lR', '-i', tmpisofile],
                           stdout=subprocess.PIPE, text=True).stdout
 
@@ -660,6 +678,11 @@ boot
             isofh.write(struct.pack(INITRDFMT, b'coreiso+', offset, ignition_img_size))
             print(f'Embedded {ignition_img_size} bytes Ignition config space at {offset}')
 
+    if args.miniso:
+        # this consumes the minimal image
+        run_verbose(['coreos-installer', 'iso', 'extract', 'pack-minimal-iso',
+                     tmpisofile, f'{tmpisofile}.minimal', "--consume"])
+
     buildmeta['images'].update({
         'live-iso': {
             'path': iso_name,